GHSA-RWXX-MRJM-WC2M

Vulnerability from github – Published: 2026-07-17 17:10 – Updated: 2026-07-17 17:10
VLAI
Summary
vLLM: ReDoS via structured_outputs.regex compiled without timeout in xgrammar and outlines backends
Details

Summary

The structured_outputs.regex API parameter passes a user-supplied regex string directly to grammar compiler backends with no compilation timeout. In the xgrammar backend, the string reaches compile_regex() with no guard. In the outlines backend, validate_regex_is_buildable() blocks structural issues (lookarounds, backreferences) but provides zero protection against exponential DFA state-space explosion. Patterns like (a+)+b pass all checks and hang the inference worker.

Root Cause

backend_xgrammar.py:91 — no timeout:

ctx = self.compiler.compile_regex(grammar_spec)

backend_outlines.py:299–330 — structural checks only, no complexity analysis:

def validate_regex_is_buildable(regex: str) -> None:
    sre_parse.parse(regex)   # AST parse only — does not detect exponential patterns
    _check_unsupported(...)  # blocks lookarounds/backrefs, not nested quantifiers

backend_outlines.py:64 — no timeout:

oc.Index(regex_string, vocabulary.inner)

Impact

Denial of service — one request with an adversarial regex pattern hangs an inference worker indefinitely.

Remediation

Wrap compile_regex() and oc.Index() calls in a thread with a deadline (e.g., 5 seconds). Add complexity analysis to validate_regex_is_buildable() to detect nested quantifier patterns before compilation.

Severity
7.5 (High)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
8.7 (High)
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
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{
  "affected": [
    {
      "package": {
        "ecosystem": "PyPI",
        "name": "vllm"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "0.24.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-55574"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-1333"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-07-17T17:10:37Z",
    "nvd_published_at": "2026-07-06T21:16:57Z",
    "severity": "HIGH"
  },
  "details": "## Summary\n\nThe `structured_outputs.regex` API parameter passes a user-supplied regex string directly to grammar compiler backends with no compilation timeout. In the xgrammar backend, the string reaches `compile_regex()` with no guard. In the outlines backend, `validate_regex_is_buildable()` blocks structural issues (lookarounds, backreferences) but provides zero protection against exponential DFA state-space explosion. Patterns like `(a+)+b` pass all checks and hang the inference worker.\n\n## Root Cause\n\n`backend_xgrammar.py:91` \u2014 no timeout:\n```python\nctx = self.compiler.compile_regex(grammar_spec)\n```\n\n`backend_outlines.py:299\u2013330` \u2014 structural checks only, no complexity analysis:\n```python\ndef validate_regex_is_buildable(regex: str) -\u003e None:\n    sre_parse.parse(regex)   # AST parse only \u2014 does not detect exponential patterns\n    _check_unsupported(...)  # blocks lookarounds/backrefs, not nested quantifiers\n```\n\n`backend_outlines.py:64` \u2014 no timeout:\n```python\noc.Index(regex_string, vocabulary.inner)\n```\n\n## Impact\n\nDenial of service \u2014 one request with an adversarial regex pattern hangs an inference worker indefinitely.\n\n## Remediation\n\nWrap `compile_regex()` and `oc.Index()` calls in a thread with a deadline (e.g., 5 seconds). Add complexity analysis to `validate_regex_is_buildable()` to detect nested quantifier patterns before compilation.",
  "id": "GHSA-rwxx-mrjm-wc2m",
  "modified": "2026-07-17T17:10:37Z",
  "published": "2026-07-17T17:10:37Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/vllm-project/vllm/security/advisories/GHSA-rwxx-mrjm-wc2m"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-55574"
    },
    {
      "type": "WEB",
      "url": "https://github.com/vllm-project/vllm/pull/45118"
    },
    {
      "type": "WEB",
      "url": "https://github.com/vllm-project/vllm/commit/2b3006076c5e9bc4cda9e03e3641388de3c5c286"
    },
    {
      "type": "WEB",
      "url": "https://github.com/pypa/advisory-database/tree/main/vulns/vllm/PYSEC-2026-2304.yaml"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/vllm-project/vllm"
    }
  ],
  "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:H",
      "type": "CVSS_V3"
    },
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "vLLM: ReDoS via structured_outputs.regex compiled without timeout in xgrammar and outlines backends"
}



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