{"id":"CVE-2026-22703","aliases":["BIT-cosign-2026-22703","GHSA-whqx-f9j3-ch6m","GO-2026-4309"],"url":"https://o3.security/vulnerability/CVE-2026-22703","summary":"Cosign verification accepts any valid Rekor entry under certain conditions","details":"### Impact\n\nA Cosign bundle can be crafted to successfully verify an artifact even if the embedded Rekor entry does not reference the artifact's digest, signature or public key. When verifying a Rekor entry, Cosign verifies the Rekor entry signature, and also compares the artifact's digest, the user's public key from either a Fulcio certificate or provided by the user, and the artifact signature to the Rekor entry contents. Without these comparisons, Cosign would accept any response from Rekor as valid. A malicious actor that has compromised a user's identity or signing key could construct a valid Cosign bundle by including any arbitrary Rekor entry, thus preventing the user from being able to audit the signing event.\n\nThis vulnerability only affects users that provide a trusted root via `--trusted-root` or when fetched automatically from a TUF repository, when no trusted key material is provided via `SIGSTORE_REKOR_PUBLIC_KEY`. When using the default flag values in Cosign v3 to sign and verify (`--use-signing-config=true` and `--new-bundle-format=true` for signing, `--new-bundle-format=true` for verification), users are unaffected. Cosign v2 users are affected using the default flag values.\n\nThis issue had previously been fixed in https://github.com/sigstore/cosign/security/advisories/GHSA-8gw7-4j42-w388 but recent refactoring caused a regression. We have added testing to prevent a future regression.\n\n#### Steps to Reproduce\n\n```\necho blob > /tmp/blob\ncosign sign-blob -y --new-bundle-format=false --bundle /tmp/bundle.1 --use-signing-config=false /tmp/blob\ncosign sign-blob -y --new-bundle-format=false --bundle /tmp/bundle.2 --use-signing-config=false /tmp/blob\njq \".rekorBundle |= $(jq .rekorBundle /tmp/bundle.2)\" /tmp/bundle.1 > /tmp/bundle.3\ncosign verify-blob --bundle /tmp/bundle.3 --certificate-identity-regexp='.*' --certificate-oidc-issuer-regexp='.*' /tmp/blob\n```\n\n### Patches\n\nUpgrade to Cosign v2.6.2 or Cosign v3.0.4. This does not affect Cosign v1.\n\n### Workarounds\n\nYou can provide trusted key material via a set of flags under certain conditions. The simplest fix is to upgrade to the latest Cosign v2 or v3 release.\n\nNote that the example below works for `cosign verify`, `cosign verify-blob, `cosign verify-blob-attestation`, and `cosign verify-attestation`.\n\n```\nSIGSTORE_REKOR_PUBLIC_KEY=<path to Rekor pub key> cosign verify-blob --use-signing-config=false --new-bundle-format=false --bundle=<path to bundle> <artifact>\n```","published":"2026-01-10T06:11:09.426Z","modified":"2026-08-24T10:25:51.746398338Z","cvss":{"score":5.5,"severity":"MEDIUM","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N"},"epss":null,"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"Go","name":"github.com/sigstore/cosign/v3","fixedVersion":"3.0.4"},{"ecosystem":"Go","name":"github.com/sigstore/cosign/v2","fixedVersion":"2.6.2"}],"fix":{"url":"https://github.com/sigstore/cosign/commit/6832fba4928c1ad69400235bbc41212de5006176","label":"sigstore/cosign@6832fba"},"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/22xxx/CVE-2026-22703.json"},{"type":"ADVISORY","url":"https://github.com/sigstore/cosign/security/advisories/GHSA-whqx-f9j3-ch6m"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-22703"},{"type":"FIX","url":"https://github.com/sigstore/cosign/commit/6832fba4928c1ad69400235bbc41212de5006176"},{"type":"FIX","url":"https://github.com/sigstore/cosign/pull/4623"},{"type":"PACKAGE","url":"https://github.com/sigstore/cosign"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-24T10:25:51.746398338Z"}}