CVE-2026-26309 (GCVE-0-2026-26309)

Vulnerability from cvelistv5 – Published: 2026-03-10 19:04 – Updated: 2026-03-10 20:12

Title

Envoy has an off-by-one write in JsonEscaper::escapeString()

Summary

Envoy is a high-performance edge/middle/service proxy. Prior to 1.37.1, 1.36.5, 1.35.8, and 1.34.13, an off-by-one write in Envoy::JsonEscaper::escapeString() can corrupt std::string null-termination, causing undefined behavior and potentially leading to crashes or out-of-bounds reads when the resulting string is later treated as a C-string. This vulnerability is fixed in 1.37.1, 1.36.5, 1.35.8, and 1.34.13.

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: none Automatable: yes Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-03-10 20:10 UTC

CWE

CWE-193 - Off-by-one Error

Assigner

GitHub_M mitre root

References

1 reference

URL	Tags
https://github.com/envoyproxy/envoy/security/advi…	x_refsource_CONFIRM

Impacted products

1 product

Vendor	Product	Version	CPE status
envoyproxy	envoy	Affected: >= 1.37.0, < 1.37.1 Affected: >= 1.36.0, < 1.36.5 Affected: >= 1.35.0, < 1.35.9 Affected: < 1.34.13	guessed

Show details on NVD website

JSON

To clipboard

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bit-envoy-2026-26309

Vulnerability from bitnami_vulndb

Published

2026-03-12 08:39

Modified

2026-09-08 08:34

Summary

Envoy has an off-by-one write in JsonEscaper::escapeString()

Details

JSON

To clipboard

{
  "affected": [
    {
      "package": {
        "ecosystem": "Bitnami",
        "name": "envoy",
        "purl": "pkg:bitnami/envoy"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "1.34.13"
            },
            {
              "introduced": "1.35.0"
            },
            {
              "fixed": "1.35.9"
            },
            {
              "introduced": "1.36.0"
            },
            {
              "fixed": "1.36.5"
            },
            {
              "introduced": "1.37.0"
            },
            {
              "fixed": "1.37.1"
            }
          ],
          "type": "SEMVER"
        }
      ],
      "severity": [
        {
          "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L",
          "type": "CVSS_V3"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-26309"
  ],
  "database_specific": {
    "cpes": [
      "cpe:2.3:a:envoyproxy:envoy:*:*:*:*:*:go:*:*"
    ],
    "severity": "Medium"
  },
  "details": "Envoy is a high-performance edge/middle/service proxy. Prior to 1.37.1, 1.36.5, 1.35.8, and 1.34.13, an off-by-one write in Envoy::JsonEscaper::escapeString() can corrupt std::string null-termination, causing undefined behavior and potentially leading to crashes or out-of-bounds reads when the resulting string is later treated as a C-string. This vulnerability is fixed in 1.37.1, 1.36.5, 1.35.8, and 1.34.13.",
  "id": "BIT-envoy-2026-26309",
  "modified": "2026-09-08T08:34:36.952Z",
  "published": "2026-03-12T08:39:42.871Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://github.com/envoyproxy/envoy/security/advisories/GHSA-56cj-wgg3-x943"
    },
    {
      "type": "WEB",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-26309"
    }
  ],
  "schema_version": "1.6.2",
  "summary": "Envoy has an off-by-one write in JsonEscaper::escapeString()"
}

FKIE_CVE-2026-26309

Vulnerability from fkie_nvd - Published: 2026-03-10 20:16 - Updated: 2026-06-17 10:26

Severity

5.3 (Medium) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
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/envoyproxy/envoy/security/advisories/GHSA-56cj-wgg3-x943	Exploit, Vendor Advisory

Impacted products

Vendor	Product	Version
envoyproxy	envoy	*
envoyproxy	envoy	*
envoyproxy	envoy	*
envoyproxy	envoy	1.37.0

JSON

To clipboard

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          "product": "envoy",
          "vendor": "envoyproxy",
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              "status": "affected",
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            },
            {
              "status": "affected",
              "version": "\u003e= 1.36.0, \u003c 1.36.5"
            },
            {
              "status": "affected",
              "version": "\u003e= 1.35.0, \u003c 1.35.9"
            },
            {
              "status": "affected",
              "version": "\u003c 1.34.13"
            }
          ]
        }
      ],
      "source": "security-advisories@github.com"
    }
  ],
  "configurations": [
    {
      "nodes": [
        {
          "cpeMatch": [
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              "criteria": "cpe:2.3:a:envoyproxy:envoy:*:*:*:*:*:*:*:*",
              "matchCriteriaId": "C4169052-E37B-4577-8689-4DA8D6AFF3F3",
              "versionEndExcluding": "1.34.13",
              "vulnerable": true
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              "versionEndExcluding": "1.35.8",
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              "vulnerable": true
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              "matchCriteriaId": "C5266F62-E0D2-4525-90B6-65921EE14F79",
              "vulnerable": true
            }
          ],
          "negate": false,
          "operator": "OR"
        }
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  ],
  "cveTags": [],
  "descriptions": [
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      "lang": "en",
      "value": "Envoy is a high-performance edge/middle/service proxy. Prior to 1.37.1, 1.36.5, 1.35.8, and 1.34.13, an off-by-one write in Envoy::JsonEscaper::escapeString() can corrupt std::string null-termination, causing undefined behavior and potentially leading to crashes or out-of-bounds reads when the resulting string is later treated as a C-string. This vulnerability is fixed in 1.37.1, 1.36.5, 1.35.8, and 1.34.13."
    },
    {
      "lang": "es",
      "value": "Envoy es un proxy de borde/intermedio/servicio de alto rendimiento. Antes de 1.37.1, 1.36.5, 1.35.8 y 1.34.13, una escritura por un byte en Envoy::JsonEscaper::escapeString() puede corromper la terminaci\u00f3n nula de std::string, causando comportamiento indefinido y potencialmente llevando a fallos o lecturas fuera de l\u00edmites cuando la cadena resultante es tratada posteriormente como una cadena C. Esta vulnerabilidad est\u00e1 corregida en 1.37.1, 1.36.5, 1.35.8 y 1.34.13."
    }
  ],
  "id": "CVE-2026-26309",
  "lastModified": "2026-06-17T10:26:03.940",
  "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"
      },
      {
        "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": "nvd@nist.gov",
        "type": "Primary"
      }
    ],
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "id": "CVE-2026-26309",
          "options": [
            {
              "exploitation": "none"
            },
            {
              "automatable": "yes"
            },
            {
              "technicalImpact": "partial"
            }
          ],
          "role": "CISA Coordinator",
          "timestamp": "2026-03-10T20:10:43.653623Z",
          "version": "2.0.3"
        }
      }
    ]
  },
  "published": "2026-03-10T20:16:35.880",
  "references": [
    {
      "source": "security-advisories@github.com",
      "tags": [
        "Exploit",
        "Vendor Advisory"
      ],
      "url": "https://github.com/envoyproxy/envoy/security/advisories/GHSA-56cj-wgg3-x943"
    }
  ],
  "sourceIdentifier": "security-advisories@github.com",
  "vulnStatus": "Analyzed",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-193"
        }
      ],
      "source": "security-advisories@github.com",
      "type": "Secondary"
    }
  ]
}

GHSA-56CJ-WGG3-X943

Vulnerability from github – Published: 2026-03-10 18:30 – Updated: 2026-03-10 22:54

Summary

Envoy affected by off-by-one write in JsonEscaper::escapeString()

Details

Summary

An off-by-one write in Envoy::JsonEscaper::escapeString() can corrupt std::string null-termination, causing undefined behavior and potentially leading to crashes or out-of-bounds reads when the resulting string is later treated as a C-string.

### Details

The bug is in the control-character escaping path in source/common/common/ json_escape_string.h:67.

The function pre-sizes result to the final length: std::string result(input.size() + required_size, '\');
For control characters (0x00..0x1f), it emits a JSON escape sequence of length 6: \u00XX.
It uses sprintf(&result[position + 1], "u%04x", ...), which writes 5 chars + a trailing NUL (\0) starting at result[position + 1].
Then it does position += 6; and writes result[position] = '\'; to overwrite the NUL.
If the control character occurs at the end of the output (e.g., the input ends with \x01), then after position += 6, position == result.size(), so result[position] is one past the end (off-by-one), violating std::string bounds/contract.

Concretely, the problematic lines are:

source/common/common/json_escape_string.h:69 (sprintf(...))
source/common/common/json_escape_string.h:72 (result[position] = '\';)

Potentially reachable from request-driven paths that escape untrusted data, e.g. invalid header reporting:

source/common/http/header_utility.cc:538 ~ source/common/http/ header_utility.cc:546 (escapes invalid header key for error text)

Even when this doesn’t immediately crash, it can break the std::string requirement that c_str()[size()] == '\0', which can later trigger UB (e.g., if passed to strlen, printf("%s"), or any C API that expects NUL termination).

```cpp //clang++ -std=c++20 -O0 -g -fsanitize=address -fno-omit-frame-pointer repro_json_escape_asan.cc -o repro_json_escape_asan ASAN_OPTIONS=abort_on_error=1 ./repro_json_escape_asan

include

#include #include #include #include

static uint64_t extraSpace(std::string_view input) { uint64_t result = 0; for (unsigned char c : input) { switch (c) { case '\"': case '\': case '\b': case '\f': case '\n': case '\r': case '\t': result += 1; break; default: if (c == 0x00 || (c > 0x00 && c <= 0x1f)) { result += 5; } break; } } return result; }

static std::string escapeString(std::string_view input, uint64_t required_size) { std::string result(input.size() + required_size, '\'); uint64_t position = 0;

for (unsigned char character : input) {
  switch (character) {
  case '\"':
    result[position + 1] = '\"';
    position += 2;
    break;
  case '\\':
    position += 2;
    break;
  case '\b':
    result[position + 1] = 'b';
    position += 2;
    break;
  case '\f':
    result[position + 1] = 'f';
    position += 2;
    break;
  case '\n':
    result[position + 1] = 'n';
    position += 2;
    break;
  case '\r':
    result[position + 1] = 'r';
    position += 2;
    break;
  case '\t':
    result[position + 1] = 't';
    position += 2;
    break;
  default:
    if (character == 0x00 || (character > 0x00 && character <= 0x1f)) {
      std::sprintf(&result[position + 1], "u%04x",

static_cast(character)); position += 6; // Off-by-one when this escape is the last output chunk: // position can become result.size(), so result[position] is out of bounds. result[position] = '\'; } else { result[position++] = static_cast(character); } break; } }

return result;

}

int main() { std::string input(4096, 'A'); input.push_back('\x01'); // ends with a control char -> triggers the buggy path at the end

const uint64_t required = extraSpace(input);
std::string escaped = escapeString(input, required);

std::printf("escaped.size=%zu\n", escaped.size());
unsigned char terminator = static_cast<unsigned char>(escaped.c_str()

[escaped.size()]); std::printf("escaped.c_str()[escaped.size()] = 0x%02x\n", terminator);

// If NUL termination is corrupted, this can read past the logical end.
std::printf("strlen(escaped.c_str()) = %zu\n",

std::strlen(escaped.c_str())); return 0; }```

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": "Go",
        "name": "github.com/envoyproxy/envoy"
      },
      "versions": [
        "1.37.0"
      ]
    },
    {
      "package": {
        "ecosystem": "Go",
        "name": "github.com/envoyproxy/envoy"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "1.36.0"
            },
            {
              "last_affected": "1.36.4"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "Go",
        "name": "github.com/envoyproxy/envoy"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "1.35.0"
            },
            {
              "last_affected": "1.35.8"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "Go",
        "name": "github.com/envoyproxy/envoy"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "last_affected": "1.34.12"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-26309"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-193"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-03-10T18:30:58Z",
    "nvd_published_at": "2026-03-10T20:16:35Z",
    "severity": "MODERATE"
  },
  "details": "### Summary\n\n  An off-by-one write in Envoy::JsonEscaper::escapeString() can corrupt\n  std::string null-termination, causing undefined behavior and potentially\n  leading to crashes or out-of-bounds reads when the resulting string is later\n  treated as a C-string.\n\n  ### Details\n\n  The bug is in the control-character escaping path in source/common/common/\n  json_escape_string.h:67.\n\n  - The function pre-sizes result to the final length: std::string\n    result(input.size() + required_size, \u0027\\\\\u0027);\n  - For control characters (0x00..0x1f), it emits a JSON escape sequence of\n    length 6: \\u00XX.\n  - It uses sprintf(\u0026result[position + 1], \"u%04x\", ...), which writes 5 chars +\n    a trailing NUL (\\0) starting at result[position + 1].\n  - Then it does position += 6; and writes result[position] = \u0027\\\\\u0027; to overwrite\n    the NUL.\n  - If the control character occurs at the end of the output (e.g., the input\n    ends with \\x01), then after position += 6, position == result.size(), so\n    result[position] is one past the end (off-by-one), violating std::string\n    bounds/contract.\n\n  Concretely, the problematic lines are:\n\n  - source/common/common/json_escape_string.h:69 (sprintf(...))\n  - source/common/common/json_escape_string.h:72 (result[position] = \u0027\\\\\u0027;)\n\n  Potentially reachable from request-driven paths that escape untrusted data,\n  e.g. invalid header reporting:\n\n  - source/common/http/header_utility.cc:538 ~ source/common/http/\n    header_utility.cc:546 (escapes invalid header key for error text)\n\n  Even when this doesn\u2019t immediately crash, it can break the std::string\n  requirement that c_str()[size()] == \u0027\\0\u0027, which can later trigger UB (e.g., if\n  passed to strlen, printf(\"%s\"), or any C API that expects NUL termination).\n  \n  \n  ```cpp\n//clang++ -std=c++20 -O0 -g -fsanitize=address -fno-omit-frame-pointer\n  repro_json_escape_asan.cc -o repro_json_escape_asan\n  ASAN_OPTIONS=abort_on_error=1 ./repro_json_escape_asan\n#include \u003ccstdint\u003e\n  #include \u003ccstdio\u003e\n  #include \u003ccstring\u003e\n  #include \u003cstring\u003e\n  #include \u003cstring_view\u003e\n\n  static uint64_t extraSpace(std::string_view input) {\n    uint64_t result = 0;\n    for (unsigned char c : input) {\n      switch (c) {\n      case \u0027\\\"\u0027:\n      case \u0027\\\\\u0027:\n      case \u0027\\b\u0027:\n      case \u0027\\f\u0027:\n      case \u0027\\n\u0027:\n      case \u0027\\r\u0027:\n      case \u0027\\t\u0027:\n        result += 1;\n        break;\n      default:\n        if (c == 0x00 || (c \u003e 0x00 \u0026\u0026 c \u003c= 0x1f)) {\n          result += 5;\n        }\n        break;\n      }\n    }\n    return result;\n  }\n\n  static std::string escapeString(std::string_view input, uint64_t\n  required_size) {\n    std::string result(input.size() + required_size, \u0027\\\\\u0027);\n    uint64_t position = 0;\n\n    for (unsigned char character : input) {\n      switch (character) {\n      case \u0027\\\"\u0027:\n        result[position + 1] = \u0027\\\"\u0027;\n        position += 2;\n        break;\n      case \u0027\\\\\u0027:\n        position += 2;\n        break;\n      case \u0027\\b\u0027:\n        result[position + 1] = \u0027b\u0027;\n        position += 2;\n        break;\n      case \u0027\\f\u0027:\n        result[position + 1] = \u0027f\u0027;\n        position += 2;\n        break;\n      case \u0027\\n\u0027:\n        result[position + 1] = \u0027n\u0027;\n        position += 2;\n        break;\n      case \u0027\\r\u0027:\n        result[position + 1] = \u0027r\u0027;\n        position += 2;\n        break;\n      case \u0027\\t\u0027:\n        result[position + 1] = \u0027t\u0027;\n        position += 2;\n        break;\n      default:\n        if (character == 0x00 || (character \u003e 0x00 \u0026\u0026 character \u003c= 0x1f)) {\n          std::sprintf(\u0026result[position + 1], \"u%04x\",\n  static_cast\u003cint\u003e(character));\n          position += 6;\n          // Off-by-one when this escape is the last output chunk:\n          // position can become result.size(), so result[position] is out of\n  bounds.\n          result[position] = \u0027\\\\\u0027;\n        } else {\n          result[position++] = static_cast\u003cchar\u003e(character);\n        }\n        break;\n      }\n    }\n\n    return result;\n  }\n\n  int main() {\n    std::string input(4096, \u0027A\u0027);\n    input.push_back(\u0027\\x01\u0027); // ends with a control char -\u003e triggers the buggy\n  path at the end\n\n    const uint64_t required = extraSpace(input);\n    std::string escaped = escapeString(input, required);\n\n    std::printf(\"escaped.size=%zu\\n\", escaped.size());\n    unsigned char terminator = static_cast\u003cunsigned char\u003e(escaped.c_str()\n  [escaped.size()]);\n    std::printf(\"escaped.c_str()[escaped.size()] = 0x%02x\\n\", terminator);\n\n    // If NUL termination is corrupted, this can read past the logical end.\n    std::printf(\"strlen(escaped.c_str()) = %zu\\n\",\n  std::strlen(escaped.c_str()));\n    return 0;\n  }```",
  "id": "GHSA-56cj-wgg3-x943",
  "modified": "2026-03-10T22:54:36Z",
  "published": "2026-03-10T18:30:58Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/envoyproxy/envoy/security/advisories/GHSA-56cj-wgg3-x943"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-26309"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/envoyproxy/envoy"
    }
  ],
  "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": "Envoy affected by off-by-one write in JsonEscaper::escapeString()"
}

WID-SEC-W-2026-0704

Vulnerability from csaf_certbund - Published: 2026-03-11 23:00 - Updated: 2026-04-01 22:00

Summary

Google Cloud Platform Envoy Proxy, Istio und Service Mesh: Mehrere Schwachstellen

Severity

Mittel

Scope

7 vulnerabilities in this advisory, including CVE-2026-26309.

CVE-2026-26309

Known affected: 7 products

Open the full advisory

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.

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-2026-26309 (GCVE-0-2026-26309)

bit-envoy-2026-26309

Vulnerability from bitnami_vulndb

FKIE_CVE-2026-26309

GHSA-56CJ-WGG3-X943

Summary

include

WID-SEC-W-2026-0704

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