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GHSA-72xp-p242-47p9medium

Symfony has a UrlGenerator Route-Requirement Bypass via Unanchored Regex Alternation → Off-Site //host URL Injection

Impact

Symfony routes can declare a requirements regex per path parameter, e.g. a route /{_locale}/blog with requirements: { _locale: 'en|fr|de' }. The Twig path() / url() helpers (backed by UrlGenerator) validate supplied parameter values against that regex before building the URL.

Source excerpt · OSV

Affected packages

Start with the recorded fix for your release branch. Check your installed version and test compatibility before upgrading. Fixing this advisory does not rule out other vulnerabilities in the release.

symfony/routing Packagist
Affected rangeRecorded fix
Earlier releases before 5.4.52Ecosystem versions5.4.52
From 6.0.0 before 6.4.40Ecosystem versions6.4.40
From 7.0.0 before 7.4.12Ecosystem versions7.4.12
From 8.0.0 before 8.0.12Ecosystem versions8.0.12

Version evidence: OSV · GHSA-72xp-p242-47p9

View original version evidence (655 explicit versions)
symfony/symfony Packagist
Affected rangeRecorded fix
Earlier releases before 5.4.52Ecosystem versions5.4.52
From 6.0.0 before 6.4.40Ecosystem versions6.4.40
From 7.0.0 before 7.4.12Ecosystem versions7.4.12
From 8.0.0 before 8.0.12Ecosystem versions8.0.12

Version evidence: OSV · GHSA-72xp-p242-47p9

View original version evidence (833 explicit versions)

Original source description

Description

Symfony routes can declare a requirements regex per path parameter, e.g. a route /{_locale}/blog with requirements: { _locale: 'en|fr|de' }. The Twig path() / url() helpers (backed by UrlGenerator) validate supplied parameter values against that regex before building the URL.

UrlGenerator constructs the validation pattern as '#^'.$req.'$#', where $req is the raw requirement string. For a requirement expressed as an alternation, e.g. _locale: 'ar|bg|...|vi|...|zh_CN' (very common), ^ and $ anchor only the first and last alternatives, so any middle alternative matches as an unanchored substring. A value like /evil.com satisfies the requirement (because it contains vi), and the generated path becomes //evil.com/...: a protocol-relative URL the browser navigates off-site.

Resolution

The UrlGenerator class now wraps the requirement in a non-capturing group so the ^ and $ anchors apply to the whole alternation.

The patch for this issue is available here for branch 5.4.

Credits

Symfony would like to thank Claude Mythos Preview (via Project Glasswing) for reporting the issue and providing the fix.

References