CVE-2026-55996
Unauthenticated Denial-of-Service via TLS SAN Stuffing in Rancher and cattle-cluster-agent
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.
INFO
Published Date :
Aug. 5, 2026, 8:16 a.m.
Last Modified :
Aug. 5, 2026, 8:16 a.m.
Remotely Exploit :
Yes !
Source :
[email protected]
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS 3.1 | MEDIUM | 404e59f5-483d-4b8a-8e7a-e67604dd8afb | ||||
| CVSS 3.1 | MEDIUM | [email protected] | ||||
| CVSS 3.1 | MEDIUM | MITRE-CVE |
Solution
- Configure CN filters for dynamiclistener TLS listeners.
- Apply available patches for Rancher server and agent.
- Restart affected Rancher components.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-55996.
| URL | Resource |
|---|---|
| https://bugzilla.suse.com/show_bug.cgi?id=CVE-2026-55996 | |
| https://github.com/rancher/rancher/security/advisories/GHSA-9jxv-832x-45q9 |
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-55996 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-55996
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-55996 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-55996 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
New CVE Received by [email protected]
Aug. 05, 2026
Action Type Old Value New Value Added Affected [{'vendor': 'SUSE', 'product': 'Rancher', 'versions': [{'status': 'affected', 'version': '2.11.0', 'lessThan': '2.11.16', 'versionType': 'semver'}, {'status': 'affected', 'version': '2.12.0', 'lessThan': '2.12.12', 'versionType': 'semver'}, {'status': 'affected', 'version': '2.13.0', 'lessThan': '2.13.8', 'versionType': 'semver'}, {'status': 'affected', 'version': '2.14.0', 'lessThan': '2.14.4', 'versionType': 'semver'}], 'packageName': 'Rancher', 'defaultStatus': 'unaffected'}] Added 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. Added CVSS V3.1 AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L Added Reference https://bugzilla.suse.com/show_bug.cgi?id=CVE-2026-55996 Added Reference https://github.com/rancher/rancher/security/advisories/GHSA-9jxv-832x-45q9