What is CVE-2026-45063?

CVE-2026-45063 is a high-severity security vulnerability in symfony/security-http (composer), affecting versions < 5.4.52. It is fixed in 5.4.52, 6.4.40, 7.4.12, 8.0.12.

Which packages are affected by CVE-2026-45063?

symfony/security-http (composer) versions < 5.4.52; symfony/symfony (composer) versions < 5.4.52.

Is there a fix for CVE-2026-45063?

Yes. CVE-2026-45063 is fixed in 5.4.52, 6.4.40, 7.4.12, 8.0.12. Upgrade to this version or later.

Is CVE-2026-45063 exploitable, and should I be worried?

Whether CVE-2026-45063 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.

What actually determines whether CVE-2026-45063 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.

CVE-2026-45063 in symfony/security-http

Q: Which packages are affected by CVE-2026-45063?

symfony/security-http (composer) versions < 5.4.52; symfony/symfony (composer) versions < 5.4.52.

Q: Is there a fix for CVE-2026-45063?

Yes. CVE-2026-45063 is fixed in 5.4.52, 6.4.40, 7.4.12, 8.0.12. Upgrade to this version or later.

Q: Is CVE-2026-45063 exploitable, and should I be worried?

Whether CVE-2026-45063 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.

Q: What actually determines whether CVE-2026-45063 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.

Q: How do I fix CVE-2026-45063?

Upgrade: symfony/security-http to 5.4.52 or later, symfony/security-http to 6.4.40 or later, symfony/security-http to 7.4.12 or later, symfony/security-http 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.

Summary

Symfony Vulnerable to 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,[email protected]) to Symfony via $_SERVER['SSL_CLIENT_S_DN']. 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.

Impact

Affected versions

symfony/security-http (< 5.4.52) symfony/security-http (>= 6.0.0-BETA1, < 6.4.40) symfony/security-http (>= 7.0.0-BETA1, < 7.4.12) symfony/security-http (>= 8.0.0-BETA1, < 8.0.12) symfony/symfony (< 5.4.52) symfony/symfony (>= 6.0.0-BETA1, < 6.4.40) symfony/symfony (>= 7.0.0-BETA1, < 7.4.12) symfony/symfony (>= 8.0.0-BETA1, < 8.0.12)

Security releases

symfony/security-http → 5.4.52 (composer) symfony/security-http → 6.4.40 (composer) symfony/security-http → 7.4.12 (composer) symfony/security-http → 8.0.12 (composer) symfony/symfony → 5.4.52 (composer) symfony/symfony → 6.4.40 (composer) symfony/symfony → 7.4.12 (composer) symfony/symfony → 8.0.12 (composer)

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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Remediation advice

Upgrade the following packages to resolve this vulnerability:

symfony/security-http to 5.4.52 or later; symfony/security-http to 6.4.40 or later; symfony/security-http to 7.4.12 or later; symfony/security-http 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-2026-45063? CVE-2026-45063 is a high-severity security vulnerability in symfony/security-http (composer), affecting versions < 5.4.52. It is fixed in 5.4.52, 6.4.40, 7.4.12, 8.0.12.
Which packages are affected by CVE-2026-45063?
- symfony/security-http (composer) (versions < 5.4.52)
- symfony/symfony (composer) (versions < 5.4.52)
Is there a fix for CVE-2026-45063? Yes. CVE-2026-45063 is fixed in 5.4.52, 6.4.40, 7.4.12, 8.0.12. Upgrade to this version or later.
Is CVE-2026-45063 exploitable, and should I be worried? Whether CVE-2026-45063 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-2026-45063 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-2026-45063?
- Upgrade symfony/security-http to 5.4.52 or later
- Upgrade symfony/security-http to 6.4.40 or later
- Upgrade symfony/security-http to 7.4.12 or later
- Upgrade symfony/security-http to 8.0.12 or later
- Upgrade symfony/symfony to 5.4.52 or later
- Upgrade symfony/symfony to 6.4.40 or later
- Upgrade symfony/symfony to 7.4.12 or later
- Upgrade symfony/symfony to 8.0.12 or later

Other vulnerabilities in symfony/security-http

CVE-IDSeverityPackage summary

CVE-2026-48489Highsymfony/security-http: Symfony: Security Firewall Bypass via failure_forward Subrequest: Unauthenticated Access to access_control-Protected GET Routes CVE-2026-45075Highsymfony/http-kernel: Symfony's HEAD Request Bypasses methods: ['GET'] Filter in #[IsGranted] / #[IsSignatureValid] / #[IsCsrfTokenValid]CVE-2026-45074Mediumsymfony/security-http: Symfony's Cas2Handler Derives CAS service URL from Client Host Header → Cross-Service Ticket Replay CVE-2026-45069Mediumsymfony/security-http: Symfony's OidcTokenHandler Accepts JWTs Missing aud/iss/exp Claims CVE-2024-51996Highsymfony/security-http: Symfony has an Authentication Bypass via RememberMe