CVE-2026-108082: Symfony: ReDoS in HeaderUtils::split() Reachable Through the Cache-Control Request Header

Severity: high (CVSS 8.7 v4.0)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.5% 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-1333

Description

Symfony is a PHP framework for web and console applications and a set of reusable PHP components. Prior to versions 5.4.54, 6.4.46, 7.4.19, and 8.1.7, 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. This issue affects symfony/http-foundation v4.1.0-BETA1 through v5.4.53, v6.0.0-BETA1 through v6.4.45, v7.0.0-BETA1 through v7.4.18, and v8.0.0-BETA1 through v8.1.6.

Affected products

Packagist Symfony/Http-Foundation: from 6.0.1 before 6.4.46; from 7.0.0 before 7.4.19; from 8.0.0 before 8.1.7; from 4.1.0 before 5.4.54; v6.0.1, v6.0.10, v6.0.11, v6.0.12, v6.0.13, v6.0.14 (+366) — fixed in 6.4.46, 7.4.19, 8.1.7, 5.4.54
Packagist Symfony/Symfony: from 6.0.1 before 6.4.46; from 7.0.0 before 7.4.19; from 8.0.0 before 8.1.7; from 4.1.0 before 5.4.54; v6.0.1, v6.0.10, v6.0.11, v6.0.12, v6.0.13, v6.0.14 (+454) — fixed in 6.4.46, 7.4.19, 8.1.7, 5.4.54

How to fix

Upgrade to a fixed version: Packagist Symfony/Http-Foundation 6.4.46, 7.4.19, 8.1.7, 5.4.54; Packagist Symfony/Symfony 6.4.46, 7.4.19, 8.1.7, 5.4.54. Check the vendor advisory for mitigations.

References

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