symfony/http-foundation security advisory

CVE-2026-108082: ReDoS in HeaderUtils::split() Reachable Through the Cache-Control Request Header in symfony/http-foundation

CVE-2026-108082 is a high-severity denial of service vulnerability in the PHP package symfony/http-foundation (CVSS 8.7), published 15 October 2026. It is fixed in 5.4.54, 6.4.46, 7.4.19 and 8.1.7, one per release line; earlier versions on each line are affected. It can be exploited without an account.

high 8.7 published 2026-10-15 · updated 2026-10-16

Affected versions: >= 5.4.1, < 5.4.54
>= 6.0.1, < 6.4.46
>= 7.0.0, < 7.4.19
>= 8.0.0, < 8.1.7
Fixed in: 5.4.54, 6.4.46, 7.4.19, 8.1.7
Newest release: 8.1.10
Severity: High · CVSS 8.7
Type: Denial of service
CWE-1333
Exploited in the wild: Not on the CISA KEV list
checked 2026-11-04

Also affects

The same advisory covers another package in our list. Fix whichever one your project installs.

symfony/symfony >= 5.4.1, < 5.4.54; >= 6.0.1, < 6.4.46; >= 7.0.0, < 7.4.19; >= 8.0.0, < 8.1.7 fixed in 5.4.54, 6.4.46, 7.4.19, 8.1.7

Is your symfony/http-foundation version affected?

Run composer show symfony/http-foundation in your project, then enter the version. We check it against this and every other known symfony/http-foundation advisory.

Who can exploit CVE-2026-108082

Access: No account. Anyone who can send a request to an app that uses the affected code.

CVSS vector: 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

Your app is only exposed if it uses the affected part of symfony/http-foundation. The advisory below says which part that is. If you are not sure, upgrade anyway: it costs less than finding out.

How to fix CVE-2026-108082 in symfony/http-foundation

Find the installed version: composer show symfony/http-foundation. If you never required it yourself, composer why symfony/http-foundation shows which package pulls it in.
Update it: composer update symfony/http-foundation --with-all-dependencies. You need the fixed version for your release line (5.4.54, 6.4.46, 7.4.19 and 8.1.7).
If Composer will not go that high, your composer.json constraint is holding it back. Widen it (for example "symfony/http-foundation": "^8.1.7" if you can take that version), or upgrade the package that requires it.
Run composer audit. It reads the same advisory data and should no longer list CVE-2026-108082.
Commit composer.lock and deploy it. On the server, run composer install --no-dev from the lock file, not composer update.

If you cannot upgrade yet

General hardening for denial of service issues while the upgrade waits. None of it replaces the fix.

Rate-limit the affected endpoint and cap request body, header and upload sizes at the web server.
If your app does not use the affected feature, note that in your audit, but still plan the upgrade.

The CVE-2026-108082 advisory

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.

Description from the CVE record, via the NVD entry for CVE-2026-108082. Advisory title: “CVE-2026-108082: ReDoS in HeaderUtils::split() Reachable Through the Cache-Control Request Header”.

References

GitHub security advisory GHSA-r925-mgvr-h9cc github.com
Symfony security advisory symfony.com
Symfony security advisory symfony.com
Pull request #66048 github.com
Pull request #66491 github.com

Other symfony/http-foundation advisories

medium CVE-2026-48736: IpUtils::PRIVATE_SUBNETS Omits IPv6 Transition Forms (6to4, NAT64, Teredo, IPv4-compatible): SSRF Bypass in NoPrivateNetworkHttpClient 2026-05-26
high CVE-2025-64500: Incorrect parsing of PATH_INFO can lead to limited authorization bypass 2025-11-12
low CVE-2024-50345: Open redirect via browser-sanitized URLs 2024-11-05
low CVE-2020-5255: Prevent cache poisoning via a Response Content-Type header 2020-03-30
high CVE-2019-18888: Prevent argument injection in a MimeTypeGuesser 2019-11-13
critical CVE-2019-10913: Reject invalid HTTP method overrides 2019-04-16

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Where this data comes from

Affected and fixed versions: the Packagist security advisories API (GitHub Advisory Database and FriendsOfPHP), the same data composer audit uses. Synced 2026-11-03.
Description, score, weakness and references: NIST National Vulnerability Database (NVD), checked 2026-11-04. This product uses data from the NVD API but is not endorsed or certified by the NVD.
Exploited-in-the-wild status: the CISA Known Exploited Vulnerabilities catalog, checked 2026-11-04.
Compiled by Daniel Lasek at Laskyr from the sources above. The summary, “who can exploit it”, “how to fix it” and hardening sections are our plain-English reading of the record and are generated from it. The quoted description is the record's own text. Spot an error? Tell us.