Vulnerability in symfony/yaml (CVE-2026-45305)
Summary
Vulnerability in symfony/yaml (CVE-2026-45305). Risk of unauthorized operations or information disclosure. Mitigation: upgrade to 8.0.12 or later.
Original description
The description as published by the source.
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.
Source: GitHub Security Advisories (Global) NVD GitHub Advisory
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2026-45305 has been found in symfony/yaml.
Risk of unauthorized operations or information disclosure. CVSS score: 7.5/10.
What to do: upgrade symfony/yaml to 8.0.12 or later.
If unsure, ask your IT team or search "symfony/yaml CVE-2026-45305" on the vendor's site.
CVE-2026-45305 (symfony/yaml) — CWE-1333 / CVSS v3 7.5
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Patched: 8.0.12 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
A vulnerability (CWE-1333) exists in symfony/yaml.
Check the vendor advisory for the affected versions of symfony/yaml.
Severity: High (CVSS 7.5/10). Risk of unauthorized operations or information disclosure.
Update to 8.0.12.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'symfony/yaml' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
-
1Identify exposure identify
grep -r 'symfony/yaml' . | grep -v node_modulesリポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で
symfony/yamlを grep し、稼働しているサービス・バージョンを把握する。 -
2Apply patch patch
Upgrade symfony/yaml to 8.0.12ステージング環境で 8.0.12 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。
-
3Post-deployment verification verify
Confirm patched version is live in productionパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。
Affected packages
Fix status by distribution
Fixed packages published by each distribution for this CVE
- Debian DEBIAN-CVE-2026-45305 symfony
- Ubuntu UBUNTU-CVE-2026-45305 symfony
References
- package github.com
- patch security-advisories@github.com
- patch security-advisories@github.com
- web github.com
- web github.com
- web symfony.com
- web github.com
- web security-advisories@github.com
- web security-advisories@github.com
- web security-advisories@github.com
- web security-advisories@github.com