GHSA-9FRC-8383-795M
Vulnerability from github – Published: 2026-05-27 21:34 – Updated: 2026-05-27 21:34
VLAI
Summary
Symfony's YAML Parser has a ReDoS via Catastrophic Backtracking in Parser::cleanup() Regex
Details
Description
Symfony\Component\Yaml\Parser::cleanup() strips the optional %YAML directive header, leading comments, and document start/end markers before parsing. The original regexes contained overlapping quantifiers, most notably '#^%YAML[: ][\d.]+.*\n#u', whose [\d.]+ and .* overlap on the dot, that exhibit catastrophic backtracking on crafted input. A single oversized %YAML directive header (or comment / document-marker line) makes the parser hang for an arbitrarily long time, denying service.
Resolution
The four regexes in Parser::cleanup() (YAML directive header, leading comments, document-start marker, document-end marker) have been rewritten with possessive quantifiers and unambiguous character classes so backtracking cannot occur.
The patch for this issue is available here for branch 5.4.
Credits
Symfony would like to thank Pietro Tirenna (Shielder) for reporting the issue and Nicolas Grekas for fixing it.
Severity
{
"affected": [
{
"package": {
"ecosystem": "Packagist",
"name": "symfony/yaml"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "5.4.52"
}
],
"type": "ECOSYSTEM"
}
]
},
{
"package": {
"ecosystem": "Packagist",
"name": "symfony/symfony"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "5.4.52"
}
],
"type": "ECOSYSTEM"
}
]
},
{
"package": {
"ecosystem": "Packagist",
"name": "symfony/symfony"
},
"ranges": [
{
"events": [
{
"introduced": "6.0.0"
},
{
"fixed": "6.4.40"
}
],
"type": "ECOSYSTEM"
}
]
},
{
"package": {
"ecosystem": "Packagist",
"name": "symfony/symfony"
},
"ranges": [
{
"events": [
{
"introduced": "7.0.0"
},
{
"fixed": "7.4.12"
}
],
"type": "ECOSYSTEM"
}
]
},
{
"package": {
"ecosystem": "Packagist",
"name": "symfony/symfony"
},
"ranges": [
{
"events": [
{
"introduced": "8.0.0"
},
{
"fixed": "8.0.12"
}
],
"type": "ECOSYSTEM"
}
]
},
{
"package": {
"ecosystem": "Packagist",
"name": "symfony/yaml"
},
"ranges": [
{
"events": [
{
"introduced": "6.0.0"
},
{
"fixed": "6.4.40"
}
],
"type": "ECOSYSTEM"
}
]
},
{
"package": {
"ecosystem": "Packagist",
"name": "symfony/yaml"
},
"ranges": [
{
"events": [
{
"introduced": "7.0.0"
},
{
"fixed": "7.4.12"
}
],
"type": "ECOSYSTEM"
}
]
},
{
"package": {
"ecosystem": "Packagist",
"name": "symfony/yaml"
},
"ranges": [
{
"events": [
{
"introduced": "8.0.0"
},
{
"fixed": "8.0.12"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [
"CVE-2026-45305"
],
"database_specific": {
"cwe_ids": [
"CWE-1333"
],
"github_reviewed": true,
"github_reviewed_at": "2026-05-27T21:34:35Z",
"nvd_published_at": null,
"severity": "LOW"
},
"details": "### Description\n\n`Symfony\\Component\\Yaml\\Parser::cleanup()` strips the optional `%YAML` directive header, leading comments, and document start/end markers before parsing. The original regexes contained overlapping quantifiers, most notably `\u0027#^%YAML[: ][\\d.]+.*\\n#u\u0027`, whose `[\\d.]+` and `.*` overlap on the dot, that exhibit catastrophic backtracking on crafted input. A single oversized `%YAML` directive header (or comment / document-marker line) makes the parser hang for an arbitrarily long time, denying service.\n\n### Resolution\n\nThe four regexes in `Parser::cleanup()` (YAML directive header, leading comments, document-start marker, document-end marker) have been rewritten with possessive quantifiers and unambiguous character classes so backtracking cannot occur.\n\nThe patch for this issue is available [here](https://github.com/symfony/symfony/commit/9749cd43c5e09b3735093623670b21b9d8a056cb) for branch 5.4.\n\n### Credits\n\nSymfony would like to thank Pietro Tirenna (Shielder) for reporting the issue and Nicolas Grekas for fixing it.",
"id": "GHSA-9frc-8383-795m",
"modified": "2026-05-27T21:34:36Z",
"published": "2026-05-27T21:34:35Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/symfony/symfony/security/advisories/GHSA-9frc-8383-795m"
},
{
"type": "WEB",
"url": "https://github.com/symfony/symfony/commit/9749cd43c5e09b3735093623670b21b9d8a056cb"
},
{
"type": "WEB",
"url": "https://github.com/FriendsOfPHP/security-advisories/blob/master/symfony/symfony/CVE-2026-45305.yaml"
},
{
"type": "WEB",
"url": "https://github.com/FriendsOfPHP/security-advisories/blob/master/symfony/yaml/CVE-2026-45305.yaml"
},
{
"type": "PACKAGE",
"url": "https://github.com/symfony/symfony"
},
{
"type": "WEB",
"url": "https://symfony.com/cve-2026-45305"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:U",
"type": "CVSS_V4"
}
],
"summary": "Symfony\u0027s YAML Parser has a ReDoS via Catastrophic Backtracking in Parser::cleanup() Regex"
}
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Sightings
| Author | Source | Type | Date | Other |
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Nomenclature
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