multicluster engine for Kubernetes 2.1: Improper Certificate Validation
CVE-2026-4740 is a high-severity improper certificate validation vulnerability in multicluster engine for Kubernetes 2.1 from Red Hat, with a CVSS 3.1 base score of 8.2 out of 10. It can be exploited with local access to the system by an attacker with administrator privileges, without any action from a user. There is no confirmed exploitation so far. EPSS estimates a 0.15% chance of exploitation within 30 days, which is low compared with other CVEs.
High severity with no evidence of exploitation so far.
What to do
- Check which version of multicluster engine for Kubernetes 2.1 you run against the affected versions below, and install the vendor's latest release.
- Read the advisory on access.redhat.com for workarounds and exact fixed builds.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Red Hat | multicluster engine for Kubernetes 2.1 | Not specified in the record | Not stated |
| Red Hat | multicluster engine for Kubernetes 2.11 | Not specified in the record | Not stated |
| Red Hat | multicluster engine for Kubernetes 2.6 | Not specified in the record | Not stated |
| Red Hat | multicluster engine for Kubernetes 2.8 | Not specified in the record | Not stated |
| Red Hat | multicluster engine for Kubernetes 2.9 | Not specified in the record | Not stated |
| Red Hat | Multicluster Engine for Kubernetes | Not specified in the record | Not stated |
| Red Hat | Advanced Cluster Management For Kubernetes | Not specified in the record | Not stated |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- LocalThe attacker needs local access or must trick a user into running something.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- HighAdministrator-level access is required first.
- User interaction
- NoneNo action by a victim is required.
- Scope
- ChangedThe attack can reach beyond the vulnerable component into other systems.
- Confidentiality
- HighAll data handled by the component can be read.
- Integrity
- HighData or code can be modified at will.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:H. Scored by CNA (redhat.com).
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 3.1 | 8.2 | High | CNA (redhat.com) |
| CVSS 3.1 | 8.2 | High | CNA |
Official description
A flaw was found in Open Cluster Management (OCM), the technology underlying Red Hat Advanced Cluster Management (ACM). Improper validation of Kubernetes client certificate renewal allows a managed cluster administrator to forge a client certificate that can be approved by the OCM controller. This enables cross-cluster privilege escalation and may allow an attacker to gain control over other managed clusters, including the hub cluster.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Improper Certificate Validation
The product does not validate, or incorrectly validates, a certificate.
How developers prevent this class of flaw
- Certificates should be carefully managed and checked to assure that data are encrypted with the intended owner's public key.
- If certificate pinning is being used, ensure that all relevant properties of the certificate are fully validated before the certificate is pinned, including the hostname.
More Improper Certificate Validation vulnerabilities (CWE-295)
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Advisories
Technical write-ups (may include proof of concept)
- blog.arfevrier.fr/open-cluster-management-cross-cluster-escape/Exploit, Third Party Advisory
Other references
Other vulnerabilities in multicluster engine for Kubernetes 2.1
- 9.1 Critical severity
- 9.4 Critical severity
- 9.3 Critical severity
- 7.5 High severity
- 7.5 High severity
- 7.7 High severity
Recent Improper Certificate Validation vulnerabilities
- 7.5 High severity
- 7.4 High severity
- 7.5 High severity
- 10.0 Critical severity
- 9.1 Critical severity
- 8.1 High severity
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