CVE-2026-118513Symfony: X.509 Authentication Impersonation via DN Value Injection (incomplete fix for CVE-2026-45063)

Official description

Authentication bypass by spoofing in X509Authenticator and X509AuthenticationListener of Symfony versions prior to 5.4.56, 6.x prior to 6.4.50, 7.x prior to 7.4.23, and 8.x prior to 8.1.11 allows an attacker holding a certificate from the application's trusted CA who can influence the CN to authenticate as an arbitrary user of the application, including a privileged one, following an incomplete fix for CVE-2026-45063. X509Authenticator extracts the user identifier from the Subject DN (Distinguished Name) that the web server passes in $_SERVER['SSL_CLIENT_S_DN']. The fix for CVE-2026-45063 anchored that extraction to an RDN (Relative Distinguished Name) boundary, but the regular expression used was not escape-aware. The expression runs against an already serialized DN, so it cannot tell an RDN separator from a separator character that occurs inside a value. Under RFC 2253, used by Apache and by nginx's $ssl_client_s_dn, a comma inside a value is escaped as \, and the expression reads it as a separator regardless. RFC 2253 also does not treat / as a separator, so it leaves it bare inside a value, while the expression treats every / as one. The legacy X509_NAME_oneline() format, used by Apache's LegacyDNStringFormat and by nginx's $ssl_client_s_dn_legacy, is the mirror image: it escapes / as \/ and leaves , bare. In that format, a certificate with no emailAddress attribute, or whose poisoned CN precedes it, authenticates as the smuggled address. To cover both RFC 2253 and the legacy X509_NAME_oneline() format, X509Authenticator and X509AuthenticationListener now split the DN into RDNs before looking for the attribute, instead of matching the attribute against the serialized string. They select the separator from the serialization, split on unescaped occurrences of that separator only, unescape each RDN afterwards with the rules of its format, and require the attribute to span a whole RDN. The accepted value grammar is unchanged. Applications that pass a per-attribute user key (such as SSL_CLIENT_S_DN_Email) and deployments whose CA generates or validates the subject are not affected by this vulnerability.

Affected packages & fixed versions

Affected products (as reported)

References

• https://github.com/symfony/symfony/security/advisories/GHSA-5w3m-mfwg-9f8r third-party-advisory
• https://github.com/symfony/symfony/commit/0f5e26b664d17cb235ca6b6d15bf4e7ac83d25cb patch
• https://github.com/symfony/symfony/commit/e885d7549a234530ce1d59121d4ac3ee35b1caea patch