CVE-2026-75939: OpenShift oc-mirror Auth Bypass Vulnerability

CVE-2026-75939 Overview

A signature verification flaw exists in the openshift/oc-mirror tool used to mirror Red Hat OpenShift release payloads into disconnected registries. The tool validates Pretty Good Privacy (PGP) release image signatures incorrectly by checking for signature errors before the entire signed body has been processed. This ordering bug allows a remote attacker who can intercept or manipulate traffic to the signature endpoint to craft a PGP message containing a valid Red Hat release key ID but a forged signature. When accepted, oc-mirror mirrors a malicious release payload into the target registry, undermining the integrity of downstream OpenShift deployments. The weakness is categorized as [CWE-347] Improper Verification of Cryptographic Signature.

Critical Impact
Attackers positioned on the network path to the signature endpoint can bypass PGP signature checks and deliver forged OpenShift release payloads into disconnected registries.

Affected Products

Red Hat openshift/oc-mirror tool
Red Hat OpenShift Container Platform disconnected mirroring workflows
Downstream registries populated by oc-mirror

Discovery Timeline

2026-09-21 - CVE-2026-75939 published to the National Vulnerability Database (NVD)
2026-09-24 - Last updated in NVD database

Technical Details for CVE-2026-75939

Vulnerability Analysis

The oc-mirror tool retrieves signed release metadata from a Red Hat signature endpoint and validates the PGP signature before pulling and mirroring container images. The validation logic evaluates signature error state prior to fully consuming the signed message body. As a result, a message that presents a legitimate Red Hat release key ID but carries a forged or malformed signature is accepted as valid.

An attacker who controls or intercepts the network path to the signature endpoint substitutes a crafted PGP message for the genuine one. oc-mirror then pulls the attacker-referenced release payload and writes it into the disconnected registry. Any cluster subsequently pulling from that registry executes attacker-controlled container images with the trust properties of a genuine Red Hat release.

Root Cause

The root cause is an incorrect ordering of operations in the PGP verification routine. The code inspects error state before the entire signed body is processed, so the final integrity check on the message contents is never enforced. This is a classic improper cryptographic signature verification defect tracked as [CWE-347].

Attack Vector

Exploitation requires a network position that allows the attacker to intercept or manipulate traffic between oc-mirror and the signature endpoint. This includes compromised upstream proxies, hostile transit networks, DNS or BGP hijacks, and TLS interception where certificate validation is weak or downgraded. No authentication is required and no user interaction is needed, but the attack complexity is high because the attacker must both control the network path and produce a PGP payload that satisfies the flawed parser. Successful exploitation results in a malicious release payload being mirrored into the trusted disconnected registry.

No public proof-of-concept code has been published for this vulnerability. See the Red Hat CVE-2026-75939 Advisory and Red Hat Bugzilla Issue #2517976 for vendor technical details.

Detection Methods for CVE-2026-75939

Indicators of Compromise

Unexpected or unsigned container image digests appearing in the disconnected registry populated by oc-mirror.
Release payload references in oc-mirror logs that do not match the digests published by Red Hat for the same release version.
TLS anomalies, unexpected certificate chains, or proxy changes on the host running oc-mirror when contacting the signature endpoint.

Detection Strategies

Compare mirrored image digests against the authoritative digest list from Red Hat for each OpenShift release before promotion.
Enable verbose logging on oc-mirror runs and alert on signature verification warnings or retries against the signature endpoint.
Perform out-of-band signature re-verification of mirrored release metadata using an independent PGP implementation.

Monitoring Recommendations

Monitor egress from mirroring hosts and alert on connections to unexpected destinations resolving as the Red Hat signature endpoint.
Track integrity of the disconnected registry with image admission controls that enforce a known-good digest allowlist.
Log and review all oc-mirror invocations, including source URLs, target registries, and the resulting image manifests.

How to Mitigate CVE-2026-75939

Immediate Actions Required

Upgrade oc-mirror to the fixed version identified in the Red Hat CVE-2026-75939 Advisory as soon as it is available for your OpenShift release stream.
Audit disconnected registries for release payloads mirrored while the vulnerable tool was in use and compare digests against Red Hat's published values.
Restrict mirroring hosts to trusted network paths and enforce strict TLS validation to the signature endpoint.

Patch Information

Red Hat has assigned and is tracking this issue under Red Hat Bugzilla Issue #2517976. Refer to the Red Hat CVE-2026-75939 Advisory for the authoritative list of fixed builds, errata, and package versions applicable to each supported OpenShift release.

Workarounds

Run oc-mirror only from hosts on a trusted, monitored network segment with no untrusted proxies in the path to the signature endpoint.
Independently verify PGP signatures on mirrored release metadata using a separate, trusted GnuPG installation before promoting images to production clusters.
Enforce image digest allowlisting at the cluster admission layer so that only Red Hat-published digests can be deployed, even if a malicious payload reaches the registry.

bash

# Configuration example: independent PGP re-verification of a mirrored release signature
gpg --import redhat-release-key.asc
gpg --verify signature-<release>.sig release-manifest-<release>.json