GitHub CLI allows attestation verification bypass through unescaped regex metacharacters

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

2.1 · 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 source

EPSS

• CVE-2026-64655: 0.34% estimated exploitation activity in the next 30 days; percentile 27.93 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary A 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. Details GitHub 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…

Published by the source

15 Oct 2026, 18:08 UTC

Last modified by the source

19 Oct 2026, 21:31 UTC

Source last checked

26 Oct 2026, 15:32 UTC

1. Revision 4 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-mm27-mwq9-fr5g

2. Revision 3 · amended · 25 Oct 2026

   Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

3. Revision 2 · amended · 24 Oct 2026

   Amended from osv record GO-2026-6767

4. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-mm27-mwq9-fr5g

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# Patch Next advisory brief: CVE-2026-64655

Advisory: GitHub CLI allows attestation verification bypass through unescaped regex metacharacters
IDs: CVE-2026-64655, GHSA-mm27-mwq9-fr5g
Record: https://patchnext.com/advisories/cve-2026-64655 (revision 4, source checked 26 Oct 2026, 15:32 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Low (CVSS 2.1)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Partial vendor fix; fixed versions by package: github.com/cli/cli/v2 2.97.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/cli/cli/v2: affected < 2.97.0; fixed in 2.97.0
- Go github.com/cli/cli: affected every version

## Suggested inspection (read-only)
- Go github.com/cli/cli/v2: check the installed version with your package manager.
- Go github.com/cli/cli: check the installed version with your package manager.

## Supported action
No complete vendor fix is recorded. Follow the primary source's mitigation guidance and check this record again before closing anything.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on github.com/cli/cli/v2, github.com/cli/cli.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GO-2026-6767 (OSV record GO-2026-6767 lists affected ranges: Go github.com/cli/cli >=0; Go github.com/cli/cli/v2 >=0 <2.97.0 (fixed))
- Verified: https://osv.dev/vulnerability/GHSA-mm27-mwq9-fr5g (OSV record GHSA-mm27-mwq9-fr5g lists affected ranges: Go github.com/cli/cli/v2 >=0 <2.97.0 (fixed))
- Verified: https://github.com/advisories/GHSA-mm27-mwq9-fr5g (GitHub-reviewed advisory GHSA-mm27-mwq9-fr5g lists affected ranges: Go github.com/cli/cli/v2 >=0 <2.97.0)

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