{"id":"GHSA-mm27-mwq9-fr5g","revision":"a19adcb8bfd2435fa172e67ed84ae894","records":[{"revision":"a19adcb8bfd2435fa172e67ed84ae894","observedAt":"2026-10-24T13:19:41.952+00:00","statement":{"source":"osv","id":"GHSA-mm27-mwq9-fr5g","aliases":["CVE-2026-64655","GO-2026-6767"],"title":"GitHub CLI allows attestation verification bypass through unescaped regex metacharacters","description":"### Summary\n\nA security vulnerability has been identified in GitHub CLI that could allow attestation verification bypass when using `gh attestation verify` with `--signer-repo` or `--signer-workflow` flags. GitHub CLI builds the certificate matcher from these flag values without escaping regex metacharacters, so a repository or workflow name is treated as a regular expression rather than a literal string. GitHub permits characters such as \u00A0`.`\u00A0 in organization, repository, and workflow path names, and \u00A0`.`\u00A0 is a regex wildcard, so a malicious actor can create a lookalike name that satisfies a matcher intended for a different, trusted signer.\n\n### Details\n\nGitHub CLI constructs a regular expression from the \u00A0`--signer-repo`\u00A0 and \u00A0`--signer-workflow`\u00A0 values and matches it against the signing certificate's SAN (Subject Alternative Name) during Sigstore attestation verification. The user-supplied value is interpolated into the pattern without escaping regex metacharacters, so any metacharacter permitted in a GitHub path is interpreted as regex syntax instead of a literal character.\n\nThe most practical case is \u00A0`.`\u00A0, which GitHub allows in org/repo names and is a regex wildcard meaning \"any single character.\" For example, an attacker-controlled repository named:\n\n`github/artifact.attestations-workflows`\n\nmatches a verifier configured for the trusted signer:\n\n`github/artifact-attestations-workflows`\n\nbecause the unescaped \u00A0`.`\u00A0 in the constructed pattern matches the \u00A0`-`\u00A0 in the attacker's name (and any other single character at that position). This affected the `--signer-repo` and `--signer-workflow` flags but did not affect the `--repo` and `--owner` flags which include an exact string comparison.\n\nIn `v2.97.0`, the GitHub CLI escapes the user-supplied signer values before they are incorporated into the SAN matcher, so they are matched as literal strings.\n\n### Impact\n\nThe practical impact is limited, exploitation requires the attacker to create a plausible lookalike repository name and produce valid Sigstore attestations from it. This could undermine supply chain verification for CI/CD pipelines or policy gates that use these flags to pin trust to a specific signing workflow. \n\n### Remediation and Mitigation\n\n1. Upgrade `gh` to `v2.97.0` or later, which escapes signer values before matching.\n2. As a workaround, use `--repo` or `--owner` flags instead of `--signer-repo` or `--signer-workflow` where applicable.\n3. Manually inspect the signing certificate SAN in attestation output to confirm the signing workflow origin.","state":0,"publishedAt":"2026-10-15T18:08:20+00:00","modifiedAt":"2026-10-19T21:41:04.7151501+00:00","affected":[{"ecosystem":"Go","name":"github.com/cli/cli/v2","ranges":[{"type":"SEMVER","events":[{"kind":"introduced","version":"0"},{"kind":"fixed","version":"2.97.0"}]}],"versions":[],"rawVersionEvidence":null}],"metrics":[{"system":"CVSS_V4","vector":"CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:A/VC:N/VI:N/VA:N/SC:N/SI:L/SA:N","score":null,"severity":null},{"system":"Publisher rating","vector":null,"score":null,"severity":"LOW"}],"references":["https://github.com/cli/cli/security/advisories/GHSA-mm27-mwq9-fr5g","https://nvd.nist.gov/vuln/detail/CVE-2026-64655","https://github.com/cli/cli/commit/55dbb4dc6b7edb10b48e3d7fc5bccd32318d1b55","https://github.com/cli/cli","https://github.com/cli/cli/releases/tag/v2.97.0"],"sourceUrl":"https://github.com/advisories/GHSA-mm27-mwq9-fr5g","license":"GitHub Advisory Database · CC-BY-4.0","key":"osv:GHSA-mm27-mwq9-fr5g","identifiers":["GHSA-mm27-mwq9-fr5g","CVE-2026-64655","GO-2026-6767"]},"retained":false,"historicalAffected":[]}],"coverage":[]}