{"id":"CVE-2026-64655","aliases":["GHSA-mm27-mwq9-fr5g","GO-2026-6767"],"url":"https://o3.security/vulnerability/CVE-2026-64655","summary":"GitHub CLI: Attestation Verification Bypass via Unescaped Regex Metacharacters in SAN Matching","details":"### 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  `.`  in organization, repository, and workflow path names, and  `.`  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  `--signer-repo`  and  `--signer-workflow`  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  `.` , 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  `.`  in the constructed pattern matches the  `-`  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.","published":"2026-08-06T18:41:54.628Z","modified":"2026-10-21T02:58:57.071811420Z","cvss":null,"epss":null,"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"Go","name":"github.com/cli/cli/v2","fixedVersion":"2.97.0"}],"fix":{"url":"https://github.com/cli/cli/commit/55dbb4dc6b7edb10b48e3d7fc5bccd32318d1b55","label":"cli/cli@55dbb4d"},"references":[{"type":"WEB","url":"https://github.com/cli/cli/releases/tag/v2.97.0"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/64xxx/CVE-2026-64655.json"},{"type":"ADVISORY","url":"https://github.com/cli/cli/security/advisories/GHSA-mm27-mwq9-fr5g"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-64655"},{"type":"FIX","url":"https://github.com/cli/cli/commit/55dbb4dc6b7edb10b48e3d7fc5bccd32318d1b55"},{"type":"PACKAGE","url":"https://github.com/cli/cli"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-10-21T02:58:57.071811420Z"}}