Vulnerability in symfony/yaml (CVE-2026-45133)
Summary
Vulnerability in symfony/yaml (CVE-2026-45133). Risk of unauthorized operations or information disclosure. Exploitable via Parser. Mitigation: upgrade to 8.0.12 or later.
Original description
The description as published by the source.
Description
Symfony\Component\Yaml\Parser is the entry point for parsing YAML strings into PHP values via Yaml::parse(). When the parser is exposed to attacker-controlled input, deeply nested mappings or sequences cause both the block-level (Parser::parseBlock()) and inline (Inline::parseSequence() / Inline::parseMapping()) parsers to recurse without a depth limit. A crafted document exhausts the PHP stack and crashes the worker.
Resolution
The Parser now tracks recursion depth in a shared ParserState object across both block-level and inline parsing, with a default limit of 128. The limit is configurable via a new $maxNestingLevel argument on Parser::__construct(), Yaml::parse() and Yaml::parseFile().
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-2026-45133 has been found in symfony/yaml.
Attackers can target a specific entry point like Parser over the network to misuse the product.
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-2026-45133" on the vendor's site.
CVE-2026-45133 (symfony/yaml) — CWE-674 / CVSS v3 7.5
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: Parser / ParserState
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-674) exists in symfony/yaml. Attackers reach the vulnerable code path via Parser without authentication.
Check the vendor advisory for the affected versions of symfony/yaml. Attack surface: Parser / ParserState.
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-2026-45133 symfony
- Ubuntu UBUNTU-CVE-2026-45133 symfony
References
- package github.com
- patch security-advisories@github.com
- web 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