CVE-2026-66794
Description
A flaw was found in the cluster-proxy-addon component of Multicluster Engine for Kubernetes. This vulnerability allows an unauthenticated attacker, who can access the user-facing route, to bypass authentication and authorization checks. By manipulating URL path segments, the attacker can proxy requests to arbitrary services across any managed cluster. This enables unauthorized access to internal services that would otherwise be protected, potentially leading to information disclosure or further compromise of the cluster environment.
Statement
This Critical vulnerability in the cluster-proxy-addon for Multicluster Engine for Kubernetes allows an unauthenticated attacker to perform Server-Side Request Forgery (SSRF). By exploiting the user-facing Route, which lacks proper authentication and authorization, an attacker can proxy requests to arbitrary services across any managed cluster, including internal services that are not otherwise exposed.
Mitigation
To mitigate this issue, restrict network access to the user-facing Route of the `cluster-proxy-addon` to trusted networks only. Implement firewall rules to limit inbound connections to the Route's exposed port, ensuring only authorized sources can reach it. This reduces the attack surface by preventing unauthenticated external access to the vulnerable proxy.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
The following CVSS metrics and score provided are preliminary and subject to review.
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 9.3 | N/A | 9.3 |
| Attack Vector | Network | N/A | Network |
| Attack Complexity | Low | N/A | Low |
| Privileges Required | None | N/A | None |
| User Interaction | None | N/A | None |
| Scope | Changed | N/A | Changed |
| Confidentiality | High | N/A | High |
| Integrity Impact | Low | N/A | Low |
| Availability Impact | None | N/A | None |
Vector
Red Hat: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:L/A:N
cve.org: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:L/A:N
Red Hat CVSS v3 Score Explanation
Revised down from AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H (10.0). Confirmed impact is unauthenticated SSRF (CWE-918) via the cluster-proxy-addon user-server route, not RCE. No demonstrated availability impact (A:N); integrity impact is speculative/target-dependent rather than confirmed (I:L). Consistent with Important-not-Critical per standing severity standard (Critical requires unauthenticated RCE) and with sibling SSRF findings in the same Glasswing audit batch.
Understanding the Weakness (CWE)
Confidentiality
Technical Impact: Read Application Data
Integrity
Technical Impact: Execute Unauthorized Code or Commands
Access Control
Technical Impact: Bypass Protection Mechanism
By providing URLs to unexpected hosts or ports, attackers can make it appear that the server is sending the request, possibly bypassing access controls such as firewalls that prevent the attackers from accessing the URLs directly. The server can be used as a proxy to conduct port scanning of hosts in internal networks, use other URLs such as that can access documents on the system (using file://), or use other protocols such as gopher:// or tftp://, which may provide greater control over the contents of requests.
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