CVE-2026-45063: Symfony: Identity Spoofing via Unanchored DN Regex in X509Authenticator
Description
X509Authenticator implements client-certificate (mTLS) authentication: the web server validates the client's certificate against a trusted CA, then passes the certificate's Subject DN (Distinguished Name: a string like CN=Alice,O=Example,emailAddress=alice@example.com) to Symfony via $SERVER['SSLCLIENTSDN']. Symfony extracts the user identifier from that string.
The extraction uses an unanchored regex that matches emailAddress= anywhere in the DN string: including inside the value of a different RDN (Relative Distinguished Name: one key=value component of the DN), such as CN. An attacker who can obtain a certificate from a trusted CA with a free-text CN can smuggle emailAddress=victim@target inside the CN value and be authenticated as the victim.
Resolution
The X509Authenticator now uses a regex that anchors the match to an RDN boundary (start of string, or following a , / / separator).
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.
Other sources
Symfony is a PHP framework for web and console applications and a set of reusable PHP components. Prior to 5.4.52, 6.4.40, 7.4.12, and 8.0.12, X509Authenticator extracts the user identifier from $SERVER['SSLCLIENTSDN'] with an unanchored regex that matches emailAddress= anywhere in the distinguished name, allowing an attacker with a trusted certificate containing emailAddress=victim inside another RDN value such as CN to authenticate as the victim. This issue is fixed in versions 5.4.52, 6.4.40, 7.4.12, and 8.0.12.
— MITRE
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
composer/symfony/symfonyto a version that resolves this vulnerability.Fixed in 8.0.12 - Upgrade
Upgrade
composer/symfony/symfonyto a version that resolves this vulnerability.Fixed in 7.4.12 - Upgrade
Upgrade
composer/symfony/symfonyto a version that resolves this vulnerability.Fixed in 6.4.40 - Upgrade
Upgrade
composer/symfony/symfonyto a version that resolves this vulnerability.Fixed in 5.4.52 - Upgrade
Upgrade
composer/symfony/security-httpto a version that resolves this vulnerability.Fixed in 8.0.12 - Upgrade
Upgrade
composer/symfony/security-httpto a version that resolves this vulnerability.Fixed in 7.4.12 - Upgrade
Upgrade
composer/symfony/security-httpto a version that resolves this vulnerability.Fixed in 6.4.40 - Upgrade
Upgrade
composer/symfony/security-httpto a version that resolves this vulnerability.Fixed in 5.4.52 - Upgrade
Upgrade
Symfony X509Authenticator (client-certificate/mTLS)to a version that resolves this vulnerability.Fixed in 5.4.52Patch ccb3f724c7ff55670a6fe3521c7bf1514cceb478 - Upgrade
Upgrade
Symfony X509Authenticator (client-certificate/mTLS)to a version that resolves this vulnerability.Fixed in 6.4.40 - Upgrade
Upgrade
Symfony X509Authenticator (client-certificate/mTLS)to a version that resolves this vulnerability.Fixed in 7.4.12 - Upgrade
Upgrade
Symfony X509Authenticator (client-certificate/mTLS)to a version that resolves this vulnerability.Fixed in 8.0.12
Event History
Frequently Asked Questions
What is the severity of CVE-2026-45063?
CVE-2026-45063 is rated with a risk score of 55, indicating a moderate severity level.
What is the primary issue associated with CVE-2026-45063?
CVE-2026-45063 relates to the implementation of client-certificate authentication in X509Authenticator, which may expose applications to certain security risks.
How do I fix CVE-2026-45063?
To mitigate CVE-2026-45063, update your Symfony components to the latest versions where the vulnerability is addressed.
Is CVE-2026-45063 exploitable remotely?
Yes, CVE-2026-45063 can potentially be exploited remotely due to its connection with client-certificate authentication.
Which Symfony versions are impacted by CVE-2026-45063?
CVE-2026-45063 affects specific versions of Symfony, particularly those that utilize the X509Authenticator for client-certificate authentication.