CVE-2026-64655
GitHub CLI (gh) is GitHub’s official command line tool. Prior to 2.97.0, gh attestation verify builds the certificate Subject Alternative Name matcher from the --signer-repo and --signer-workflow flag values without escaping regex metacharacters, so a user-supplied repository or workflow name is treated as a regular expression rather than a literal string. Because GitHub permits characters such as . in organization, repository, and workflow path names and . is a regex wildcard, an attacker can register a lookalike name (for example github/artifact.attestations-workflows) that satisfies a matcher intended for a different trusted signer (github/artifact-attestations-workflows), bypassing the intended Sigstore attestation verification. Exploitation requires the attacker to create a plausible lookalike repository and produce valid attestations from it, which could undermine supply chain verification for CI/CD pipelines or policy gates that pin trust to a specific signing workflow. This issue is fixed in version 2.97.0.
CSIRTS triage
- What
- Attestation verification can be bypassed via unescaped regex metacharacters in Subject Alternative Name matching.
- Who is affected
- GitHub CLI users relying on attestation verification.
- Urgency
- Severity unknown but auth-bypass is critical in nature; investigate and patch immediately.
- Action
- Upgrade GitHub CLI to the patched version addressing CVE-2026-64655.
AI-assisted analysis generated from the source advisory — verify against the original.
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Exploitation outlook
- Low exploitation risk0.32% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 25% of all EPSS-scored CVEs.
Advisory coverage (2)
External references
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