# 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.

- **Severity:** High 8.7 (`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`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 15 Oct 2026
- **Updated:** 15 Oct 2026
- **Also known as:** DEBIAN-CVE-2026-109449, GHSA-7rpj-w9pf-39rr, UBUNTU-CVE-2026-109449

## 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 (Uncontrolled Recursion)

## Which versions are affected by CVE-2026-109449?


## How do I fix CVE-2026-109449?

Upgrade to a fixed version.

## Is CVE-2026-109449 being exploited?

There is no known exploitation of CVE-2026-109449 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-109449 and fix it if it is affected.

What it is: 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.
Exploitation: There is no known exploitation of CVE-2026-109449 in the wild and no public exploit code.

Affected product: sensiolabs symfony. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-109449/ (Markdown: https://insights.sbomify.com/CVE-2026-109449/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-109449
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-109449
- OSV: https://osv.dev/vulnerability/CVE-2026-109449

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-109449/
Summaries are generated and may contain mistakes; the official description above is the record.