---
id: "CVE-2026-108082"
kind: "vulnerability"
aliases: ["CVE-2026-108082", "GHSA-r925-mgvr-h9cc"]
title: "Symfony: ReDoS in HeaderUtils::split() Reachable Through the Cache-Control Request Header"
severity: "high"
cvss: 8.7
epss: 0.0048
exploited: false
status: "open"
category: "package"
products: [{"name": "symfony/http-foundation", "fixed": ["6.4.46"], "affected": ">= 6.0.1, < 6.4.46", "ecosystem": "composer"}, {"name": "symfony/http-foundation", "fixed": ["7.4.19"], "affected": ">= 7.0.0, < 7.4.19", "ecosystem": "composer"}, {"name": "symfony/http-foundation", "fixed": ["8.1.7"], "affected": ">= 8.0.0, < 8.1.7", "ecosystem": "composer"}, {"name": "symfony/symfony", "fixed": ["6.4.46"], "affected": ">= 6.0.1, < 6.4.46", "ecosystem": "composer"}, {"name": "symfony/symfony", "fixed": ["7.4.19"], "affected": ">= 7.0.0, < 7.4.19", "ecosystem": "composer"}, {"name": "symfony/symfony", "fixed": ["8.1.7"], "affected": ">= 8.0.0, < 8.1.7", "ecosystem": "composer"}, {"name": "symfony/http-foundation", "fixed": ["5.4.54"], "affected": ">= 4.1.0, < 5.4.54", "ecosystem": "composer"}, {"name": "symfony/symfony", "fixed": ["5.4.54"], "affected": ">= 4.1.0, < 5.4.54", "ecosystem": "composer"}]
ecosystems: ["composer"]
tags: ["composer", "cwe-1333", "package", "php", "self-hosted", "symfony", "web-app"]
not_affected_if: ["auth-required"]
published_at: "2026-10-15T15:17:22+00:00"
first_seen_at: "2026-10-27T19:04:56+00:00"
updated_at: "2026-10-27T19:33:18+00:00"
sources: [{"source": "ghsa", "url": "https://github.com/advisories/GHSA-r925-mgvr-h9cc", "first_seen_at": "2026-10-27T19:04:56+00:00"}, {"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-108082", "first_seen_at": "2026-10-27T19:33:18+00:00"}]
---

# Symfony: ReDoS in HeaderUtils::split() Reachable Through the Cache-Control Request Header

HeaderUtils::split() in Symfony's HttpFoundation uses a regular expression that backtracks exponentially on runs of whitespace in the Cache-Control header. A single unauthenticated request with such a header costs close to a second of CPU per 17 spaces, doubling with each extra space, and from 18 spaces on the header's directives are silently dropped.

_Summary, check and fix written by a model from the sources; labelled as such._

## Affected

- composer:symfony/http-foundation affected >= 6.0.1, < 6.4.46 fixed 6.4.46
- composer:symfony/http-foundation affected >= 7.0.0, < 7.4.19 fixed 7.4.19
- composer:symfony/http-foundation affected >= 8.0.0, < 8.1.7 fixed 8.1.7
- composer:symfony/symfony affected >= 6.0.1, < 6.4.46 fixed 6.4.46
- composer:symfony/symfony affected >= 7.0.0, < 7.4.19 fixed 7.4.19
- composer:symfony/symfony affected >= 8.0.0, < 8.1.7 fixed 8.1.7
- composer:symfony/http-foundation affected >= 4.1.0, < 5.4.54 fixed 5.4.54
- composer:symfony/symfony affected >= 4.1.0, < 5.4.54 fixed 5.4.54

## How to check

- Run `composer show symfony/http-foundation` and `composer show symfony/symfony` and compare against the fixed versions below.
- Check the installed version of the Symfony packages in `composer.lock`.

## Fix

- Upgrade symfony/http-foundation and symfony/symfony to `6.4.48`, `7.4.21` or `8.1.9` on their branches (the 6.4.46 to 6.4.47, 7.4.19 to 7.4.20 and 8.1.7 to 8.1.8 releases broke whitespace separators).
- Upgrade 5.4 installs to `5.4.54`.

## Timeline

- 2026-10-27T19:04:56+00:00 ghsa https://github.com/advisories/GHSA-r925-mgvr-h9cc
- 2026-10-27T19:33:18+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-108082

## From the sources

### Description

`HeaderUtils::split()` parsed header values with a pattern whose token alternative also matched whitespace, followed by a `(?<!\s)` lookbehind. A run of whitespace placed before a separator could be divided among the iterations of the enclosing repetition in exponentially many ways, and the engine tried all of them before settling. `HeaderBag` calls it for the `Cache-Control` header whenever a `Request` is built, so any application handling HTTP requests is reachable, with no authentication.

A single request carrying such a header costs close to a second of CPU (813 ms for a run of 17 spaces in an 8 KB header on PHP 8.5, doubling with each extra space). From 18 spaces on, `preg_match_all()` gives up at `pcre.backtrack_limit` and `split()` returns an empty array, so every directive of the header is silently dropped.

### Resolution

The pattern now consumes whitespace only when more of the value follows it, so a value can no longer end on whitespace, nothing has to be given back, and every quantifier is possessive. The first release of this fix broke splitting on a whitespace separator: `HeaderUtils::split('foo bar', ' ')` returned a single value in 6.4.46 to 6.4.47, 7.4.19 to 7.4.20 and 8.1.7 to 8.1.8. Whitespace characters used as separators are now left out of the whitespace branch, which 6.4.48, 7.4.21 and 8.1.9 contain.

The patches for this issue are available [here](https://github.com/symfony/symfony/commit/343a1772ce6ac03e48b228d2d7168d19750e3f36) for branch 5.4 (and forward-ported to 6.4, 7.4, 8.1 and 8.2).

### Credits

Symfony would like to thank [r3verii](https://github.com/r3verii) for reporting the issue and Nicolas Grekas for providing the fix.

Symfony would also like to thank [Bruno Dias](https://github.com/cx-bruno-dias) from Checkmarx for his help getting a CVE assigned.

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