CVE-2026-25651

Versions 0.2.1 and 0.3.0 of client-certificate-auth contain an open redirect vulnerability. The middleware unconditionally redirects HTTP requests to HTTPS using the unvalidated Host header, allowing an attacker to redirect users to arbitrary domains.

Vulnerable Code

// lib/clientCertificateAuth.js (versions 0.2.1, 0.3.0)
if (!req.secure && req.header('x-forwarded-proto') != 'https') {
  return res.redirect('https://' + req.header('host') + req.url);
}

Attack Scenario

1. Attacker crafts a link: http://vulnerable-app.example.com/login
2. When victim clicks, attacker intercepts and injects header: Host: attacker.com
3. Server responds: 302 Found → https://attacker.com/login
4. Victim is redirected to attacker-controlled site

Exploitability

Exploitation requires that HTTP traffic reaches the Node.js application without TLS termination setting x-forwarded-proto: https. This condition is uncommon in production deployments behind modern reverse proxies or load balancers, which limits real-world exploitability.

Workarounds

If upgrading is not immediately possible:

1. Block HTTP traffic at the network/load balancer level
2. Ensure your reverse proxy always sets x-forwarded-proto: https
3. Add middleware before clientCertificateAuth to validate the Host header against an allowlist

References

• CWE-601: URL Redirection to Untrusted Site
• OWASP: Unvalidated Redirects and Forwards
• Fix Commit

• Phishing: Attackers can use trusted domain links to redirect victims to credential-harvesting pages
• OAuth/SSO Token Theft: In authentication flows, authorization codes or tokens may leak via redirect
• Referer Leakage: Sensitive URL parameters may be exposed to attacker domains via the Referer header
• Cache Poisoning: In deployments with shared caches, malicious redirects may be cached and served to other users

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.

CVE-2026-25651 has a CVSS score of 6.1 (Medium). The vector is network-reachable, no privileges required, and user interaction required. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (1.0.0); upgrading removes the vulnerable code path.

Kodem intelligence

The vulnerable redirect behavior has been completely removed in version 1.0.0.

npm install client-certificate-auth@^1.0.0

1. What is CVE-2026-25651? CVE-2026-25651 is a medium-severity open redirect vulnerability in client-certificate-auth (npm), affecting versions >= 0.2.1, < 1.0.0. It is fixed in 1.0.0. Untrusted input controls a URL used for redirection, which can forward users to attacker-controlled sites.
2. How severe is CVE-2026-25651? CVE-2026-25651 has a CVSS score of 6.1 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of client-certificate-auth are affected by CVE-2026-25651? client-certificate-auth (npm) versions >= 0.2.1, < 1.0.0 is affected.
4. Is there a fix for CVE-2026-25651? Yes. CVE-2026-25651 is fixed in 1.0.0. Upgrade to this version or later.
5. Is CVE-2026-25651 exploitable, and should I be worried? Whether CVE-2026-25651 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
6. What actually determines whether CVE-2026-25651 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.
7. How do I fix CVE-2026-25651? Upgrade client-certificate-auth to 1.0.0 or later.