Live › vulnerability › CVE-2026-108082
Go to dashboardHeaderUtils::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 written from the sources below. Check the originals before acting.
First seen by InfraStack 2026-10-27 19:04 UTC, 0h before NVD. All times on this page are UTC.
Any application built on Symfony HttpFoundation that builds a Request from incoming HTTP traffic is reachable, because HeaderBag parses Cache-Control on every Request. Exposure is over the internet with no authentication, so public-facing services are the priority. Command-line jobs that never build a Request from untrusted headers are less exposed.
| Product | Ecosystem | Affected | Fixed in |
|---|---|---|---|
| symfony/http-foundation | composer | >= 6.0.1, < 6.4.46 | 6.4.46 |
| symfony/http-foundation | composer | >= 7.0.0, < 7.4.19 | 7.4.19 |
| symfony/http-foundation | composer | >= 8.0.0, < 8.1.7 | 8.1.7 |
| symfony/symfony | composer | >= 6.0.1, < 6.4.46 | 6.4.46 |
| symfony/symfony | composer | >= 7.0.0, < 7.4.19 | 7.4.19 |
| symfony/symfony | composer | >= 8.0.0, < 8.1.7 | 8.1.7 |
| symfony/http-foundation | composer | >= 4.1.0, < 5.4.54 | 5.4.54 |
| symfony/symfony | composer | >= 4.1.0, < 5.4.54 | 5.4.54 |
composer show symfony/http-foundation and composer show symfony/symfony and compare against the fixed versions below.composer.lock.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).5.4.54.Each row is the first time that source carried this signal. The analyst’s rows are its own findings.
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.
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 for branch 5.4 (and forward-ported to 6.4, 7.4, 8.1 and 8.2).
Symfony would like to thank r3verii for reporting the issue and Nicolas Grekas for providing the fix.
Symfony would also like to thank Bruno Dias from Checkmarx for his help getting a CVE assigned.
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