Summary
Symfony has a UrlGenerator Route-Requirement Bypass via Unanchored Regex Alternation → Off-Site //host URL Injection
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.
Impact
Untrusted input controls a URL used for redirection, which can forward users to attacker-controlled sites. Typical impact: phishing and credential harvesting via a trusted domain.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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symfony/routing to 5.4.52 or later; symfony/routing to 6.4.40 or later; symfony/routing to 7.4.12 or later; symfony/routing to 8.0.12 or later; symfony/symfony to 5.4.52 or later; symfony/symfony to 6.4.40 or later; symfony/symfony to 7.4.12 or later; symfony/symfony to 8.0.12 or later
Kodem Kai can prioritize this vulnerability in your dependency tree and generate a fix recommendation.
Frequently Asked Questions
- What is CVE-2026-45065? CVE-2026-45065 is a medium-severity open redirect vulnerability in symfony/routing (composer), affecting versions < 5.4.52. It is fixed in 5.4.52, 6.4.40, 7.4.12, 8.0.12. Untrusted input controls a URL used for redirection, which can forward users to attacker-controlled sites.
- Which packages are affected by CVE-2026-45065?
symfony/routing(composer) (versions < 5.4.52)symfony/symfony(composer) (versions < 5.4.52)
- Is there a fix for CVE-2026-45065? Yes. CVE-2026-45065 is fixed in 5.4.52, 6.4.40, 7.4.12, 8.0.12. Upgrade to this version or later.
- Is CVE-2026-45065 exploitable, and should I be worried? Whether CVE-2026-45065 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-45065 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-45065?
- Upgrade
symfony/routingto 5.4.52 or later - Upgrade
symfony/routingto 6.4.40 or later - Upgrade
symfony/routingto 7.4.12 or later - Upgrade
symfony/routingto 8.0.12 or later - Upgrade
symfony/symfonyto 5.4.52 or later - Upgrade
symfony/symfonyto 6.4.40 or later - Upgrade
symfony/symfonyto 7.4.12 or later - Upgrade
symfony/symfonyto 8.0.12 or later
- Upgrade