CVE-2026-55996 — MEDIUM (4.3)

Vulnerability Description

A denial-of-service vulnerability was identified in multiple TLS listeners in Rancher. Both the cattle-cluster-agent component running in downstream clusters and the Rancher server itself use the dynamiclistener library to serve TLS traffic. Without an effective CN filter configured, dynamiclistener automatically appended to each serving certificate any hostname presented via Server Name Indication (SNI) in incoming TLS requests. An unauthenticated attacker with network access within the affected cluster could send a large number of TLS requests with distinct hostnames, causing the serving certificate to accumulate an unbounded number of Subject Alternative Names (SANs). Eventually, the certificate grows large enough that TLS handshakes fail with an excessive message size error, causing a denial of service on the affected listeners.

CVSS Score

4.3

MEDIUM

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L

Attack Vector

NETWORK

Attack Complexity

LOW

Privileges Required

LOW

User Interaction

NONE

Scope

UNCHANGED

Confidentiality

NONE

Integrity

NONE

Availability

LOW

Related Weaknesses (CWE)

CWE-770

References

FAQ

What is CVE-2026-55996?

CVE-2026-55996 is a vulnerability with a CVSS score of 4.3 (MEDIUM). A denial-of-service vulnerability was identified in multiple TLS listeners in Rancher. Both the cattle-cluster-agent component running in downstream clusters and the Rancher server itself use the dyna...

How severe is CVE-2026-55996?

CVE-2026-55996 has been rated MEDIUM with a CVSS base score of 4.3/10. Review the CVSS metrics above for detailed severity breakdown.

Is there a patch for CVE-2026-55996?

Check the references section above for vendor advisories and patch information. Review vendor security bulletins for remediation guidance.