What’s Vulnerable › Vulnerabilities

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

• Severity: high (CVSS 8.7 v4.0)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.4% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-10-15 · updated 2026-10-16
• Weakness: CWE-674

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.

References

• https://github.com/symfony/symfony/pull/65690
• https://github.com/symfony/symfony/pull/66720
• https://github.com/symfony/symfony/pull/66723
• 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

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