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🛡️ CVE-2026-45305 — symfony

🟠 CVSS 7.5 — High ✅ No Known Exploit CWE-1333 NVD
7.5
CVSS Score
0 Low4 Medium7 High9 Critical10

Description

Symfony's YAML Parser has a ReDoS via Catastrophic Backtracking in Parser::cleanup() Regex

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](https://github.com/symfony/symfony/commit/9749cd43c5e09b3735093623670b21b9d8a056cb) for branch 5.4.

Credits

Symfony would like to thank Pietro Tirenna (Shielder) for reporting the issue and Nicolas Grekas for fixing it.

How this vulnerability can be exploited

This issue can be reached over the network, attack complexity is low, an attacker needs no privileges on the target. No user interaction is required. The scope is unchanged, so the impact stays within the vulnerable component. Rated impact: confidentiality none, integrity none, availability high.

CVSS metrics in full

The score comes from this vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

  • Attack vector: Network — reachable from anywhere that can route to the service.
  • Attack complexity: Low — the attack works reliably, with no preparation.
  • Privileges required: None — an unauthenticated stranger can try it.
  • User interaction: None — nobody has to be tricked into anything.
  • Scope: Unchanged — the damage stays inside the vulnerable component.
  • Confidentiality impact: None.
  • Integrity impact: None.
  • Availability impact: High — total loss, or loss the attacker controls.

Weakness class

CVE-2026-45305 is classified as CWE-1333: Inefficient Regular Expression Complexity. A regular expression backtracks catastrophically on crafted input, consuming CPU out of proportion to input size.

Affected software

CVE-2026-45305 is recorded against 3 packages.

  • symfony (from 8.0.0 up to 8.0.12)
  • symfony/symfony (from 8.0.0 up to 8.0.12)
  • symfony/yaml (from 8.0.0 up to 8.0.12)

Timeline and source

Published on 14 July 2026 and last revised on 15 July 2026. No public exploit is currently recorded for this entry. A vendor advisory or fix has been published. Record sourced from NVD.

References

github.com
github.com
github.com
github.com
github.com
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Other advisories for this package

symfony has other advisories on record. If you are patching this one, these are worth checking on the same host:

Same weakness in other software

These advisories are the same class of weakness (CWE-1333: Inefficient Regular Expression Complexity) in other software:

CVE-2026-45305 on other distributions

Each distribution ships its own build and its own fixed version. Pick the one you run:

Details

Severity HIGH
CVSS Score 7.5
CVSS Vector CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CWE CWE-1333
Public Exploit ✅ No
Source NVD
Published 2026-07-14
Updated 2026-08-20
Modified 2026-07-15

Affected Packages

Software From version Fixed in
symfony 8.0.0 8.0.12
symfony/symfony 8.0.0 8.0.12
symfony/yaml 8.0.0 8.0.12

Similar Threats

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