Unauthenticated Denial-of-Service via TLS SAN Stuffing in Rancher and cattle-cluster-agent

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-55996
StatePUBLISHED
Assignersuse
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-08-05 08:16:34 UTC
Updated2026-08-05 20:17:11 UTC
DescriptionA 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.

Risk And Classification

Primary CVSS: v3.1 4.3 MEDIUM from [email protected]

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

EPSS: 0.001500000 probability, percentile 0.047130000 (date 2026-08-05)

Problem Types: CWE-770 | CWE-770 CWE-770 Allocation of Resources Without Limits or Throttling

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary4.3MEDIUMCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
3.1CNACVSS4.3MEDIUMCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
Low

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

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA SUSE Rancher affected 2.11.0 2.11.16 semver Not specified
CNA SUSE Rancher affected 2.12.0 2.12.12 semver Not specified
CNA SUSE Rancher affected 2.13.0 2.13.8 semver Not specified
CNA SUSE Rancher affected 2.14.0 2.14.4 semver Not specified

References

ReferenceSourceLinkTags
bugzilla.suse.com/show_bug.cgi [email protected] bugzilla.suse.com
github.com/rancher/rancher/security/advisories/GHSA-9jxv-832x-45q9 [email protected] github.com
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