Vulnerability-Lookup

CVE-2026-73556 (GCVE-0-2026-73556)

Vulnerability from cvelistv5 – Published: 2026-08-13 14:56 – Updated: 2026-08-14 16:52

Title

vLLM: ReDoS via structured_outputs.regex in the lm-format-enforcer backend (no compile timeout) — missed sibling of CVE-2026-55574

Summary

vLLM is an inference and serving engine for large language models. Prior to 0.26.0, the structured_outputs.regex parameter in vllm/v1/structured_output/backend_lm_format_enforcer.py is passed to lmformatenforcer.RegexParser without compile_regex_with_timeout or validation in validate_structured_output_request_lm_format_enforcer, allowing an unauthenticated /v1/completions request against the lm-format-enforcer backend to consume a CPU core and stall the structured-output engine path with a catastrophic regular expression. This issue is fixed in version 0.26.0.

Severity

5.3 (Medium)


                        
                          CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

SSVC

Exploitation: poc Automatable: yes Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-08-14 16:52 UTC

CWE

CWE-400 - Uncontrolled Resource Consumption
CWE-1333 - Inefficient Regular Expression Complexity

Assigner

GitHub_M mitre root

References

4 references

URL	Tags
https://github.com/vllm-project/vllm/security/adv…	x_refsource_CONFIRM
https://github.com/vllm-project/vllm/pull/47595	x_refsource_MISC
https://github.com/vllm-project/vllm/commit/c9a78…	x_refsource_MISC
https://github.com/vllm-project/vllm/releases/tag…	x_refsource_MISC

Impacted products

1 product

Vendor	Product	Version	CPE status
vllm-project	vllm	Affected: < 0.26.0	guessed

Show details on NVD website

JSON

To clipboard

{
  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "other": {
              "content": {
                "id": "CVE-2026-73556",
                "options": [
                  {
                    "Exploitation": "poc"
                  },
                  {
                    "Automatable": "yes"
                  },
                  {
                    "Technical Impact": "partial"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-08-14T16:52:13.326454Z",
                "version": "2.0.3"
              },
              "type": "ssvc"
            }
          }
        ],
        "providerMetadata": {
          "dateUpdated": "2026-08-14T16:52:40.458Z",
          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
        "references": [
          {
            "tags": [
              "exploit"
            ],
            "url": "https://github.com/vllm-project/vllm/security/advisories/GHSA-48jh-3gj7-fg8v"
          }
        ],
        "title": "CISA ADP Vulnrichment"
      }
    ],
    "cna": {
      "affected": [
        {
          "product": "vllm",
          "vendor": "vllm-project",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 0.26.0"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "vLLM is an inference and serving engine for large language models. Prior to 0.26.0, the structured_outputs.regex parameter in vllm/v1/structured_output/backend_lm_format_enforcer.py is passed to lmformatenforcer.RegexParser without compile_regex_with_timeout or validation in validate_structured_output_request_lm_format_enforcer, allowing an unauthenticated /v1/completions request against the lm-format-enforcer backend to consume a CPU core and stall the structured-output engine path with a catastrophic regular expression. This issue is fixed in version 0.26.0."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "attackComplexity": "LOW",
            "attackVector": "NETWORK",
            "availabilityImpact": "LOW",
            "baseScore": 5.3,
            "baseSeverity": "MEDIUM",
            "confidentialityImpact": "NONE",
            "integrityImpact": "NONE",
            "privilegesRequired": "NONE",
            "scope": "UNCHANGED",
            "userInteraction": "NONE",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L",
            "version": "3.1"
          }
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-400",
              "description": "CWE-400: Uncontrolled Resource Consumption",
              "lang": "en",
              "type": "CWE"
            }
          ]
        },
        {
          "descriptions": [
            {
              "cweId": "CWE-1333",
              "description": "CWE-1333: Inefficient Regular Expression Complexity",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-13T14:56:52.569Z",
        "orgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
        "shortName": "GitHub_M"
      },
      "references": [
        {
          "name": "https://github.com/vllm-project/vllm/security/advisories/GHSA-48jh-3gj7-fg8v",
          "tags": [
            "x_refsource_CONFIRM"
          ],
          "url": "https://github.com/vllm-project/vllm/security/advisories/GHSA-48jh-3gj7-fg8v"
        },
        {
          "name": "https://github.com/vllm-project/vllm/pull/47595",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/vllm-project/vllm/pull/47595"
        },
        {
          "name": "https://github.com/vllm-project/vllm/commit/c9a788eedc412acceaa5112e0d44624b49841577",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/vllm-project/vllm/commit/c9a788eedc412acceaa5112e0d44624b49841577"
        },
        {
          "name": "https://github.com/vllm-project/vllm/releases/tag/v0.26.0",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/vllm-project/vllm/releases/tag/v0.26.0"
        }
      ],
      "source": {
        "advisory": "GHSA-48jh-3gj7-fg8v",
        "discovery": "UNKNOWN"
      },
      "title": "vLLM: ReDoS via structured_outputs.regex in the lm-format-enforcer backend (no compile timeout) \u2014 missed sibling of CVE-2026-55574"
    }
  },
  "cveMetadata": {
    "assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
    "assignerShortName": "GitHub_M",
    "cveId": "CVE-2026-73556",
    "datePublished": "2026-08-13T14:56:52.569Z",
    "dateReserved": "2026-08-12T20:53:46.380Z",
    "dateUpdated": "2026-08-14T16:52:40.458Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
    "epss": {
      "cve": "CVE-2026-73556",
      "date": "2026-09-17",
      "epss": "0.00315",
      "percentile": "0.24432"
    },
    "nvd": {
      "cve": {
        "affected": [
          {
            "affectedData": [
              {
                "product": "vllm",
                "vendor": "vllm-project",
                "versions": [
                  {
                    "status": "affected",
                    "version": "\u003c 0.26.0"
                  }
                ]
              }
            ],
            "source": "security-advisories@github.com"
          }
        ],
        "cveTags": [],
        "descriptions": [
          {
            "lang": "en",
            "value": "vLLM is an inference and serving engine for large language models. Prior to 0.26.0, the structured_outputs.regex parameter in vllm/v1/structured_output/backend_lm_format_enforcer.py is passed to lmformatenforcer.RegexParser without compile_regex_with_timeout or validation in validate_structured_output_request_lm_format_enforcer, allowing an unauthenticated /v1/completions request against the lm-format-enforcer backend to consume a CPU core and stall the structured-output engine path with a catastrophic regular expression. This issue is fixed in version 0.26.0."
          }
        ],
        "id": "CVE-2026-73556",
        "lastModified": "2026-09-09T20:58:37.713",
        "metrics": {
          "cvssMetricV31": [
            {
              "cvssData": {
                "attackComplexity": "LOW",
                "attackVector": "NETWORK",
                "availabilityImpact": "LOW",
                "baseScore": 5.3,
                "baseSeverity": "MEDIUM",
                "confidentialityImpact": "NONE",
                "integrityImpact": "NONE",
                "privilegesRequired": "NONE",
                "scope": "UNCHANGED",
                "userInteraction": "NONE",
                "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L",
                "version": "3.1"
              },
              "exploitabilityScore": 3.9,
              "impactScore": 1.4,
              "source": "security-advisories@github.com",
              "type": "Secondary"
            }
          ],
          "ssvcV203": [
            {
              "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
              "ssvcData": {
                "id": "CVE-2026-73556",
                "options": [
                  {
                    "exploitation": "poc"
                  },
                  {
                    "automatable": "yes"
                  },
                  {
                    "technicalImpact": "partial"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-08-14T16:52:13.326454Z",
                "version": "2.0.3"
              }
            }
          ]
        },
        "published": "2026-08-13T15:20:17.927",
        "references": [
          {
            "source": "security-advisories@github.com",
            "url": "https://github.com/vllm-project/vllm/commit/c9a788eedc412acceaa5112e0d44624b49841577"
          },
          {
            "source": "security-advisories@github.com",
            "url": "https://github.com/vllm-project/vllm/pull/47595"
          },
          {
            "source": "security-advisories@github.com",
            "url": "https://github.com/vllm-project/vllm/releases/tag/v0.26.0"
          },
          {
            "source": "security-advisories@github.com",
            "url": "https://github.com/vllm-project/vllm/security/advisories/GHSA-48jh-3gj7-fg8v"
          },
          {
            "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
            "url": "https://github.com/vllm-project/vllm/security/advisories/GHSA-48jh-3gj7-fg8v"
          }
        ],
        "sourceIdentifier": "security-advisories@github.com",
        "vulnStatus": "Awaiting Analysis",
        "weaknesses": [
          {
            "description": [
              {
                "lang": "en",
                "value": "CWE-400"
              },
              {
                "lang": "en",
                "value": "CWE-1333"
              }
            ],
            "source": "security-advisories@github.com",
            "type": "Secondary"
          }
        ]
      }
    },
    "redhat_vex": {
      "aggregate_severity": "Important",
      "current_release_date": "2026-09-16T16:56:26+00:00",
      "cve": "CVE-2026-73556",
      "id": "CVE-2026-73556",
      "initial_release_date": "2026-08-13T14:56:52.569000+00:00",
      "product_status:known_affected": "22",
      "product_status:known_not_affected": "4",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "vllm: vLLM: Denial of Service via Regular Expression processing",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-73556.json",
      "version": "3"
    },
    "suse_vex": {
      "aggregate_severity": "moderate",
      "current_release_date": "2026-08-14T17:12:56Z",
      "cve": "CVE-2026-73556",
      "id": "CVE-2026-73556",
      "initial_release_date": "2026-08-14T17:12:56Z",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2026-73556",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2026-73556.json",
      "version": "2"
    },
    "vulnrichment": {
      "containers": {
        "adp": [
          {
            "metrics": [
              {
                "other": {
                  "content": {
                    "id": "CVE-2026-73556",
                    "options": [
                      {
                        "Exploitation": "poc"
                      },
                      {
                        "Automatable": "yes"
                      },
                      {
                        "Technical Impact": "partial"
                      }
                    ],
                    "role": "CISA Coordinator",
                    "timestamp": "2026-08-14T16:52:13.326454Z",
                    "version": "2.0.3"
                  },
                  "type": "ssvc"
                }
              }
            ],
            "providerMetadata": {
              "dateUpdated": "2026-08-14T16:52:34.468Z",
              "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
              "shortName": "CISA-ADP"
            },
            "references": [
              {
                "tags": [
                  "exploit"
                ],
                "url": "https://github.com/vllm-project/vllm/security/advisories/GHSA-48jh-3gj7-fg8v"
              }
            ],
            "title": "CISA ADP Vulnrichment"
          }
        ],
        "cna": {
          "affected": [
            {
              "product": "vllm",
              "vendor": "vllm-project",
              "versions": [
                {
                  "status": "affected",
                  "version": "\u003c 0.26.0"
                }
              ]
            }
          ],
          "descriptions": [
            {
              "lang": "en",
              "value": "vLLM is an inference and serving engine for large language models. Prior to 0.26.0, the structured_outputs.regex parameter in vllm/v1/structured_output/backend_lm_format_enforcer.py is passed to lmformatenforcer.RegexParser without compile_regex_with_timeout or validation in validate_structured_output_request_lm_format_enforcer, allowing an unauthenticated /v1/completions request against the lm-format-enforcer backend to consume a CPU core and stall the structured-output engine path with a catastrophic regular expression. This issue is fixed in version 0.26.0."
            }
          ],
          "metrics": [
            {
              "cvssV3_1": {
                "attackComplexity": "LOW",
                "attackVector": "NETWORK",
                "availabilityImpact": "LOW",
                "baseScore": 5.3,
                "baseSeverity": "MEDIUM",
                "confidentialityImpact": "NONE",
                "integrityImpact": "NONE",
                "privilegesRequired": "NONE",
                "scope": "UNCHANGED",
                "userInteraction": "NONE",
                "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L",
                "version": "3.1"
              }
            }
          ],
          "problemTypes": [
            {
              "descriptions": [
                {
                  "cweId": "CWE-400",
                  "description": "CWE-400: Uncontrolled Resource Consumption",
                  "lang": "en",
                  "type": "CWE"
                }
              ]
            },
            {
              "descriptions": [
                {
                  "cweId": "CWE-1333",
                  "description": "CWE-1333: Inefficient Regular Expression Complexity",
                  "lang": "en",
                  "type": "CWE"
                }
              ]
            }
          ],
          "providerMetadata": {
            "dateUpdated": "2026-08-13T14:56:52.569Z",
            "orgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
            "shortName": "GitHub_M"
          },
          "references": [
            {
              "name": "https://github.com/vllm-project/vllm/security/advisories/GHSA-48jh-3gj7-fg8v",
              "tags": [
                "x_refsource_CONFIRM"
              ],
              "url": "https://github.com/vllm-project/vllm/security/advisories/GHSA-48jh-3gj7-fg8v"
            },
            {
              "name": "https://github.com/vllm-project/vllm/pull/47595",
              "tags": [
                "x_refsource_MISC"
              ],
              "url": "https://github.com/vllm-project/vllm/pull/47595"
            },
            {
              "name": "https://github.com/vllm-project/vllm/commit/c9a788eedc412acceaa5112e0d44624b49841577",
              "tags": [
                "x_refsource_MISC"
              ],
              "url": "https://github.com/vllm-project/vllm/commit/c9a788eedc412acceaa5112e0d44624b49841577"
            },
            {
              "name": "https://github.com/vllm-project/vllm/releases/tag/v0.26.0",
              "tags": [
                "x_refsource_MISC"
              ],
              "url": "https://github.com/vllm-project/vllm/releases/tag/v0.26.0"
            }
          ],
          "source": {
            "advisory": "GHSA-48jh-3gj7-fg8v",
            "discovery": "UNKNOWN"
          },
          "title": "vLLM: ReDoS via structured_outputs.regex in the lm-format-enforcer backend (no compile timeout) \u2014 missed sibling of CVE-2026-55574"
        }
      },
      "cveMetadata": {
        "assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
        "assignerShortName": "GitHub_M",
        "cveId": "CVE-2026-73556",
        "datePublished": "2026-08-13T14:56:52.569Z",
        "dateReserved": "2026-08-12T20:53:46.380Z",
        "dateUpdated": "2026-08-13T14:56:52.569Z",
        "state": "PUBLISHED"
      },
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}

FKIE_CVE-2026-73556

Vulnerability from fkie_nvd - Published: 2026-08-13 15:20 - Updated: 2026-09-09 20:58

Severity

5.3 (Medium) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

Summary

References

	URL	Tags
	security-advisories@github.com	https://github.com/vllm-project/vllm/commit/c9a788eedc412acceaa5112e0d44624b49841577
	security-advisories@github.com	https://github.com/vllm-project/vllm/pull/47595
	security-advisories@github.com	https://github.com/vllm-project/vllm/releases/tag/v0.26.0
	security-advisories@github.com	https://github.com/vllm-project/vllm/security/advisories/GHSA-48jh-3gj7-fg8v
	134c704f-9b21-4f2e-91b3-4a467353bcc0	https://github.com/vllm-project/vllm/security/advisories/GHSA-48jh-3gj7-fg8v

Impacted products

	Vendor	Product	Version

JSON

To clipboard

{
  "affected": [
    {
      "affectedData": [
        {
          "product": "vllm",
          "vendor": "vllm-project",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 0.26.0"
            }
          ]
        }
      ],
      "source": "security-advisories@github.com"
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "vLLM is an inference and serving engine for large language models. Prior to 0.26.0, the structured_outputs.regex parameter in vllm/v1/structured_output/backend_lm_format_enforcer.py is passed to lmformatenforcer.RegexParser without compile_regex_with_timeout or validation in validate_structured_output_request_lm_format_enforcer, allowing an unauthenticated /v1/completions request against the lm-format-enforcer backend to consume a CPU core and stall the structured-output engine path with a catastrophic regular expression. This issue is fixed in version 0.26.0."
    }
  ],
  "id": "CVE-2026-73556",
  "lastModified": "2026-09-09T20:58:37.713",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "LOW",
          "attackVector": "NETWORK",
          "availabilityImpact": "LOW",
          "baseScore": 5.3,
          "baseSeverity": "MEDIUM",
          "confidentialityImpact": "NONE",
          "integrityImpact": "NONE",
          "privilegesRequired": "NONE",
          "scope": "UNCHANGED",
          "userInteraction": "NONE",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L",
          "version": "3.1"
        },
        "exploitabilityScore": 3.9,
        "impactScore": 1.4,
        "source": "security-advisories@github.com",
        "type": "Secondary"
      }
    ],
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "id": "CVE-2026-73556",
          "options": [
            {
              "exploitation": "poc"
            },
            {
              "automatable": "yes"
            },
            {
              "technicalImpact": "partial"
            }
          ],
          "role": "CISA Coordinator",
          "timestamp": "2026-08-14T16:52:13.326454Z",
          "version": "2.0.3"
        }
      }
    ]
  },
  "published": "2026-08-13T15:20:17.927",
  "references": [
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/vllm-project/vllm/commit/c9a788eedc412acceaa5112e0d44624b49841577"
    },
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/vllm-project/vllm/pull/47595"
    },
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/vllm-project/vllm/releases/tag/v0.26.0"
    },
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/vllm-project/vllm/security/advisories/GHSA-48jh-3gj7-fg8v"
    },
    {
      "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
      "url": "https://github.com/vllm-project/vllm/security/advisories/GHSA-48jh-3gj7-fg8v"
    }
  ],
  "sourceIdentifier": "security-advisories@github.com",
  "vulnStatus": "Awaiting Analysis",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-400"
        },
        {
          "lang": "en",
          "value": "CWE-1333"
        }
      ],
      "source": "security-advisories@github.com",
      "type": "Secondary"
    }
  ]
}

GHSA-48JH-3GJ7-FG8V

Vulnerability from github – Published: 2026-09-04 21:37 – Updated: 2026-09-04 21:37

Summary

vLLM: ReDoS via structured_outputs.regex in the lm-format-enforcer backend (no compile timeout) — missed sibling of GHSA-rwxx-mrjm-wc2m

Details

Summary

The fix for GHSA-rwxx-mrjm-wc2m ("ReDoS via structured_outputs.regex compiled without timeout") wrapped the regex compile in the xgrammar and outlines backends with compile_regex_with_timeout (and, for outlines, validate_regex_is_buildable). The lm-format-enforcer backend was left unguarded: it compiles the attacker-supplied regex with no timeout and no buildability check. A single request with a catastrophic regex hangs the structured-output compile step and stalls the engine worker (denial of service).

Affected code (HEAD d6d39c1)

vllm/v1/structured_output/backend_lm_format_enforcer.py: - line 110: character_level_parser = lmformatenforcer.RegexParser(grammar_spec) — builds an interegular FSM from the attacker regex synchronously, no timeout. - line 155: validate_structured_output_request_lm_format_enforcer returns immediately on if so_params.regex: — no validation.

Sibling backends that WERE patched by GHSA-rwxx: - backend_xgrammar.py:92 → compile_regex_with_timeout(...). - backend_outlines.py:65 → compile_regex_with_timeout(...) (plus validate_regex_is_buildable).

lm-format-enforcer uses the same interegular DFA-construction primitive the advisory cites for the outlines backend.

Reproduction (runtime-verified against the sink)

The sink lmformatenforcer.RegexParser(<regex>) was exercised directly (this is exactly what the backend calls):

baseline  '[0-9]{3}'          -> 0.0002 s
attacker  '(a{1,300}){300}'   -> DID NOT COMPLETE in 20 s (one core pegged at 100% in interegular FSM construction)

End-to-end: start vllm serve <model> --structured-outputs-config '{"backend":"lm-format-enforcer"}', then POST /v1/completions with {"structured_outputs":{"regex":"(a{1,300}){300}"}, ...}. The request never returns; because grammar compile runs in the engine's structured-output path, concurrent requests stall = worker-level DoS. The identical request against the outlines backend is bounded by compile_regex_with_timeout and returns a clean error.

Impact

Unauthenticated denial of service (vLLM ships with no authentication by default). One request pegs a CPU core and blocks the structured-output engine path.

Reachability precondition: the operator must have selected backend=lm-format-enforcer via --structured-outputs-config (the default is auto → xgrammar). This is the same opt-in tier as the outlines backend that GHSA-rwxx already covered.

Suggested remediation

Route the lm-format-enforcer regex compile (backend_lm_format_enforcer.py:110) through the same compile_regex_with_timeout guard already applied to the xgrammar and outlines backends, and reject un-buildable / oversized patterns in validate_structured_output_request_lm_format_enforcer.

Severity

5.3 (Medium)


                  
                    CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

Show details on source website

JSON

To clipboard

{
  "affected": [
    {
      "package": {
        "ecosystem": "PyPI",
        "name": "vllm"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "0.26.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-73556"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-1333",
      "CWE-400"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-09-04T21:37:00Z",
    "nvd_published_at": "2026-08-13T15:20:17Z",
    "severity": "MODERATE"
  },
  "details": "### Summary\n\nThe fix for `GHSA-rwxx-mrjm-wc2m` (\"ReDoS via `structured_outputs.regex` compiled without timeout\") wrapped the regex compile in the **xgrammar** and **outlines** backends with `compile_regex_with_timeout` (and, for outlines, `validate_regex_is_buildable`). The **lm-format-enforcer** backend was left unguarded: it compiles the attacker-supplied regex with no timeout and no buildability check. A single request with a catastrophic regex hangs the structured-output compile step and stalls the engine worker (denial of service).\n\n### Affected code (HEAD d6d39c1)\n\n`vllm/v1/structured_output/backend_lm_format_enforcer.py`:\n- line 110: `character_level_parser = lmformatenforcer.RegexParser(grammar_spec)` \u2014 builds an `interegular` FSM from the attacker regex synchronously, **no timeout**.\n- line 155: `validate_structured_output_request_lm_format_enforcer` returns immediately on `if so_params.regex:` \u2014 **no validation**.\n\nSibling backends that WERE patched by GHSA-rwxx:\n- `backend_xgrammar.py:92` \u2192 `compile_regex_with_timeout(...)`.\n- `backend_outlines.py:65` \u2192 `compile_regex_with_timeout(...)` (plus `validate_regex_is_buildable`).\n\nlm-format-enforcer uses the same `interegular` DFA-construction primitive the advisory cites for the outlines backend.\n\n### Reproduction (runtime-verified against the sink)\n\nThe sink `lmformatenforcer.RegexParser(\u003cregex\u003e)` was exercised directly (this is exactly what the backend calls):\n\n```\nbaseline  \u0027[0-9]{3}\u0027          -\u003e 0.0002 s\nattacker  \u0027(a{1,300}){300}\u0027   -\u003e DID NOT COMPLETE in 20 s (one core pegged at 100% in interegular FSM construction)\n```\n\nEnd-to-end: start `vllm serve \u003cmodel\u003e --structured-outputs-config \u0027{\"backend\":\"lm-format-enforcer\"}\u0027`, then `POST /v1/completions` with `{\"structured_outputs\":{\"regex\":\"(a{1,300}){300}\"}, ...}`. The request never returns; because grammar compile runs in the engine\u0027s structured-output path, concurrent requests stall = worker-level DoS. The identical request against the outlines backend is bounded by `compile_regex_with_timeout` and returns a clean error.\n\n### Impact\n\nUnauthenticated denial of service (vLLM ships with no authentication by default). One request pegs a CPU core and blocks the structured-output engine path.\n\n**Reachability precondition:** the operator must have selected `backend=lm-format-enforcer` via `--structured-outputs-config` (the default is `auto` \u2192 xgrammar). This is the same opt-in tier as the outlines backend that GHSA-rwxx already covered.\n\n### Suggested remediation\n\nRoute the lm-format-enforcer regex compile (`backend_lm_format_enforcer.py:110`) through the same `compile_regex_with_timeout` guard already applied to the xgrammar and outlines backends, and reject un-buildable / oversized patterns in `validate_structured_output_request_lm_format_enforcer`.",
  "id": "GHSA-48jh-3gj7-fg8v",
  "modified": "2026-09-04T21:37:00Z",
  "published": "2026-09-04T21:37:00Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/vllm-project/vllm/security/advisories/GHSA-48jh-3gj7-fg8v"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-73556"
    },
    {
      "type": "WEB",
      "url": "https://github.com/vllm-project/vllm/pull/47595"
    },
    {
      "type": "WEB",
      "url": "https://github.com/vllm-project/vllm/commit/c9a788eedc412acceaa5112e0d44624b49841577"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/vllm-project/vllm"
    },
    {
      "type": "WEB",
      "url": "https://github.com/vllm-project/vllm/releases/tag/v0.26.0"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L",
      "type": "CVSS_V3"
    }
  ],
  "summary": "vLLM: ReDoS via structured_outputs.regex in the lm-format-enforcer backend (no compile timeout) \u2014 missed sibling of GHSA-rwxx-mrjm-wc2m"
}

PYSEC-2026-3933

Vulnerability from pysec - Published: 2026-09-10 09:45 - Updated: 2026-09-10 11:02

Details

Summary

Affected code (HEAD d6d39c1)

lm-format-enforcer uses the same interegular DFA-construction primitive the advisory cites for the outlines backend.

Reproduction (runtime-verified against the sink)

The sink lmformatenforcer.RegexParser(<regex>) was exercised directly (this is exactly what the backend calls):

baseline  '[0-9]{3}'          -> 0.0002 s
attacker  '(a{1,300}){300}'   -> DID NOT COMPLETE in 20 s (one core pegged at 100% in interegular FSM construction)

Impact

Unauthenticated denial of service (vLLM ships with no authentication by default). One request pegs a CPU core and blocks the structured-output engine path.

Suggested remediation

Severity

5.3 (Medium)


                  
                    CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

Impacted products

Name	purl
vllm	pkg:pypi/vllm

Aliases

JSON

To clipboard

{
  "affected": [
    {
      "package": {
        "ecosystem": "PyPI",
        "name": "vllm",
        "purl": "pkg:pypi/vllm"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "0.26.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "0.0.1",
        "0.1.0",
        "0.1.1",
        "0.1.2",
        "0.1.3",
        "0.1.4",
        "0.1.5",
        "0.1.6",
        "0.1.7",
        "0.10.0",
        "0.10.1",
        "0.10.1.1",
        "0.10.2",
        "0.11.0",
        "0.11.1",
        "0.11.2",
        "0.12.0",
        "0.13.0",
        "0.14.0",
        "0.14.1",
        "0.15.0",
        "0.15.1",
        "0.16.0",
        "0.17.0",
        "0.17.1",
        "0.18.0",
        "0.18.1",
        "0.19.0",
        "0.19.1",
        "0.2.0",
        "0.2.1",
        "0.2.1.post1",
        "0.2.2",
        "0.2.3",
        "0.2.4",
        "0.2.5",
        "0.2.6",
        "0.2.7",
        "0.20.0",
        "0.20.1",
        "0.20.2",
        "0.21.0",
        "0.22.0",
        "0.22.1",
        "0.23.0",
        "0.24.0",
        "0.25.0",
        "0.25.1",
        "0.3.0",
        "0.3.1",
        "0.3.2",
        "0.3.3",
        "0.4.0",
        "0.4.0.post1",
        "0.4.1",
        "0.4.2",
        "0.4.3",
        "0.5.0",
        "0.5.0.post1",
        "0.5.1",
        "0.5.2",
        "0.5.3",
        "0.5.3.post1",
        "0.5.4",
        "0.5.5",
        "0.6.0",
        "0.6.1",
        "0.6.1.post1",
        "0.6.1.post2",
        "0.6.2",
        "0.6.3",
        "0.6.3.post1",
        "0.6.4",
        "0.6.4.post1",
        "0.6.5",
        "0.6.6",
        "0.6.6.post1",
        "0.7.0",
        "0.7.1",
        "0.7.2",
        "0.7.3",
        "0.8.0",
        "0.8.1",
        "0.8.2",
        "0.8.3",
        "0.8.4",
        "0.8.5",
        "0.8.5.post1",
        "0.9.0",
        "0.9.0.1",
        "0.9.1",
        "0.9.2"
      ]
    }
  ],
  "aliases": [
    "CVE-2026-73556",
    "GHSA-48jh-3gj7-fg8v"
  ],
  "details": "### Summary\n\nThe fix for `GHSA-rwxx-mrjm-wc2m` (\"ReDoS via `structured_outputs.regex` compiled without timeout\") wrapped the regex compile in the **xgrammar** and **outlines** backends with `compile_regex_with_timeout` (and, for outlines, `validate_regex_is_buildable`). The **lm-format-enforcer** backend was left unguarded: it compiles the attacker-supplied regex with no timeout and no buildability check. A single request with a catastrophic regex hangs the structured-output compile step and stalls the engine worker (denial of service).\n\n### Affected code (HEAD d6d39c1)\n\n`vllm/v1/structured_output/backend_lm_format_enforcer.py`:\n- line 110: `character_level_parser = lmformatenforcer.RegexParser(grammar_spec)` \u2014 builds an `interegular` FSM from the attacker regex synchronously, **no timeout**.\n- line 155: `validate_structured_output_request_lm_format_enforcer` returns immediately on `if so_params.regex:` \u2014 **no validation**.\n\nSibling backends that WERE patched by GHSA-rwxx:\n- `backend_xgrammar.py:92` \u2192 `compile_regex_with_timeout(...)`.\n- `backend_outlines.py:65` \u2192 `compile_regex_with_timeout(...)` (plus `validate_regex_is_buildable`).\n\nlm-format-enforcer uses the same `interegular` DFA-construction primitive the advisory cites for the outlines backend.\n\n### Reproduction (runtime-verified against the sink)\n\nThe sink `lmformatenforcer.RegexParser(\u003cregex\u003e)` was exercised directly (this is exactly what the backend calls):\n\n```\nbaseline  \u0027[0-9]{3}\u0027          -\u003e 0.0002 s\nattacker  \u0027(a{1,300}){300}\u0027   -\u003e DID NOT COMPLETE in 20 s (one core pegged at 100% in interegular FSM construction)\n```\n\nEnd-to-end: start `vllm serve \u003cmodel\u003e --structured-outputs-config \u0027{\"backend\":\"lm-format-enforcer\"}\u0027`, then `POST /v1/completions` with `{\"structured_outputs\":{\"regex\":\"(a{1,300}){300}\"}, ...}`. The request never returns; because grammar compile runs in the engine\u0027s structured-output path, concurrent requests stall = worker-level DoS. The identical request against the outlines backend is bounded by `compile_regex_with_timeout` and returns a clean error.\n\n### Impact\n\nUnauthenticated denial of service (vLLM ships with no authentication by default). One request pegs a CPU core and blocks the structured-output engine path.\n\n**Reachability precondition:** the operator must have selected `backend=lm-format-enforcer` via `--structured-outputs-config` (the default is `auto` \u2192 xgrammar). This is the same opt-in tier as the outlines backend that GHSA-rwxx already covered.\n\n### Suggested remediation\n\nRoute the lm-format-enforcer regex compile (`backend_lm_format_enforcer.py:110`) through the same `compile_regex_with_timeout` guard already applied to the xgrammar and outlines backends, and reject un-buildable / oversized patterns in `validate_structured_output_request_lm_format_enforcer`.",
  "id": "PYSEC-2026-3933",
  "modified": "2026-09-10T11:02:35.442026Z",
  "published": "2026-09-10T09:45:00.190897Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/vllm-project/vllm/security/advisories/GHSA-48jh-3gj7-fg8v"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-73556"
    },
    {
      "type": "WEB",
      "url": "https://github.com/vllm-project/vllm/pull/47595"
    },
    {
      "type": "WEB",
      "url": "https://github.com/vllm-project/vllm/commit/c9a788eedc412acceaa5112e0d44624b49841577"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/vllm-project/vllm"
    },
    {
      "type": "WEB",
      "url": "https://github.com/vllm-project/vllm/releases/tag/v0.26.0"
    },
    {
      "type": "PACKAGE",
      "url": "https://pypi.org/project/vllm"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/advisories/GHSA-48jh-3gj7-fg8v"
    }
  ],
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L",
      "type": "CVSS_V3"
    }
  ],
  "summary": "vLLM: ReDoS via structured_outputs.regex in the lm-format-enforcer backend (no compile timeout) \u2014 missed sibling of GHSA-rwxx-mrjm-wc2m"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.

Related by attack behaviour

Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.

Action not permitted

CVE-2026-73556 (GCVE-0-2026-73556)

FKIE_CVE-2026-73556

GHSA-48JH-3GJ7-FG8V

Summary

Affected code (HEAD d6d39c1)

Reproduction (runtime-verified against the sink)

Impact

Suggested remediation

PYSEC-2026-3933

Summary

Affected code (HEAD d6d39c1)

Reproduction (runtime-verified against the sink)

Impact

Suggested remediation

Tags

Sightings

Nomenclature

Related by attack behaviour