CVE-2026-109449 Symfony: Unbounded Nesting in the Expression Parser Lets Untrusted Expressions Crash the Process
An attacker can crash the PHP process by submitting deeply nested expressions to the Symfony Expression Language parser, causing a denial of service.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-109449?
CVE-2026-109449 is a high-severity denial of service vulnerability in sensiolabs symfony, published on 15 Oct 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Weakness: CWE-674
Which versions are affected by CVE-2026-109449?
How do I fix CVE-2026-109449?
Upgrade to a fixed version.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-109449 being exploited?
There is no known exploitation of CVE-2026-109449 in the wild and no public exploit code.
Sources
Also known as DEBIAN-CVE-2026-109449, GHSA-7rpj-w9pf-39rr, UBUNTU-CVE-2026-109449.