CVE-2026-109449 sensiolabs CVE debrief

Who should care

Defenders responsible for Symfony Expression Language deployments, developers validating expressions written by users, and teams parsing untrusted expressions should assess exposure and prioritize patching.

Why it matters

Defenders should care about CVE-2026-109449 because it allows untrusted expressions to crash the PHP process, potentially leading to denial-of-service attacks, and affects applications validating user-supplied expressions.

• Crash of PHP process due to deeply nested expressions
• Potential denial-of-service (DoS) attacks through crafted expressions
• Increased risk for applications validating user-supplied expressions
• Need for verification of affected versions and patch application

Technical summary

The Symfony Expression Language component has a vulnerability in versions prior to 5.4.54, 6.4.48, 7.4.21, and 8.1.9, where the parser built its node tree with no bound on its depth, allowing expressions made of tens of thousands of nested unary operators, array literals, binary operators, or property accesses to crash the PHP process. This issue affects applications validating user-supplied expressions and those parsing untrusted expressions. Defenders should prioritize verifying and applying patches for affected versions.

Defensive priority

Defenders should prioritize verifying and applying patches for Symfony Expression Language versions prior to 5.4.54, 6.4.48, 7.4.21, and 8.1.9.

Recommended defensive actions

• Verify and apply patches for Symfony Expression Language versions prior to 5.4.54, 6.4.48, 7.4.21, and 8.1.9.
• Review and update affected systems and applications using Symfony Expression Language.
• Monitor for and respond to potential crashes caused by untrusted expressions.
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up.
• Review compensating controls for exposed systems while remediation is scheduled and verified.
• Check relevant monitoring, detection, and logs for exposed assets that need extra review.
• Track exceptions, retest remediated assets, and close the item only after evidence is documented.

Evidence notes

The CVE record and source item provide details on the vulnerability in Symfony Expression Language, including affected versions and references to patches. Evidence limits are based on source-provided information. Defenders should verify affected systems, apply patches, and review compensating controls. The vulnerability 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.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.