High [CVE-2026-56865] Supply chain compromise via transparency log tile verification bypass

A malicious GOPROXY was previously capable of forging up to two sumdb tiles that allow for a requested module to bypass the GOSUMDB check and persist attacker-controlled module content to a local Go module cache. This attack allows for a malicious GOPROXY to serve malicious module content that cannot be detected by evaluating the transparency log.

All tiles are now correctly verified against their parents. In order to determine if you have been affected: rm -r go.sum go.work.sum vendor/ && go mod tidy A flaw was found in golang.org/x/mod/sumdb/tlog.

This allowed the proxy to bypass integrity checks and serve malicious module content to a local Go module cache, which would then go undetected by the transparency log. This could lead to a supply chain compromise where users unknowingly incorporate compromised modules.

Exploitation of this vulnerability requires the victim to use a malicious or compromised Go module proxy (GOPROXY). The default GOPROXY (proxy.golang.org) is operated by Google.

Users of custom or third-party Go proxies are at higher risk. Red Hat severity: Important — CVSS 8.8 (CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H).

Weakness: CWE-347. Affected Red Hat products: Red Hat Advanced Cluster Security for Kubernetes 4.11; ExternalDNS Operator; OpenShift Pipelines; Red Hat OpenShift distributed tracing 3.