CVE-2026-64655: Github.com/cli/cli/v2 GitHub CLI Allows Attestation Verification Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-mm27-mwq9-fr5g",
  "modified" : "2026-10-15T18:08:20Z",
  "published" : "2026-10-15T18:08:20Z",
  "aliases" : [ "CVE-2026-64655" ],
  "summary" : "GitHub CLI allows attestation verification bypass through unescaped regex metacharacters",
  "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.",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "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"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/cli/cli/v2"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "2.97.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "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" : "WEB",
    "url" : "https://github.com/cli/cli/commit/55dbb4dc6b7edb10b48e3d7fc5bccd32318d1b55"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/cli/cli"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/cli/cli/releases/tag/v2.97.0"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-185" ],
    "severity" : "LOW",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-10-15T18:08:20Z",
    "nvd_published_at" : "2026-08-06T22:18:13Z"
  }
}