CVE-2026-22703

CVE-2026-22703 is a medium-severity security vulnerability in github.com/sigstore/cosign/v3 (go), affecting versions <= 3.0.3. It is fixed in 3.0.4, 2.6.2.

Summary

Steps to Reproduce

echo blob > /tmp/blob
cosign sign-blob -y --new-bundle-format=false --bundle /tmp/bundle.1 --use-signing-config=false /tmp/blob
cosign sign-blob -y --new-bundle-format=false --bundle /tmp/bundle.2 --use-signing-config=false /tmp/blob
jq ".rekorBundle |= $(jq .rekorBundle /tmp/bundle.2)" /tmp/bundle.1 > /tmp/bundle.3
cosign verify-blob --bundle /tmp/bundle.3 --certificate-identity-regexp='.*' --certificate-oidc-issuer-regexp='.*' /tmp/blob

Workarounds

You 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.

Note that the example below works for cosign verify, cosign verify-blob, cosign verify-blob-attestation, and cosign verify-attestation`.

SIGSTORE_REKOR_PUBLIC_KEY=<path to Rekor pub key> cosign verify-blob --use-signing-config=false --new-bundle-format=false --bundle=<path to bundle> <artifact>

Impact

A 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.

This 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.

This 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.

CVE-2026-22703 has a CVSS score of 5.5 (Medium). The vector is requires local access, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (3.0.4, 2.6.2); upgrading removes the vulnerable code path.

Affected versions

github.com/sigstore/cosign/v3 (<= 3.0.3) github.com/sigstore/cosign/v2 (<= 2.6.1)

Security releases

github.com/sigstore/cosign/v3 → 3.0.4 (go) github.com/sigstore/cosign/v2 → 2.6.2 (go)

Kodem intelligence

Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.

Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.

See it in your environment

Remediation advice

Upgrade to Cosign v2.6.2 or Cosign v3.0.4. This does not affect Cosign v1.

Frequently Asked Questions

  1. What is CVE-2026-22703? CVE-2026-22703 is a medium-severity security vulnerability in github.com/sigstore/cosign/v3 (go), affecting versions <= 3.0.3. It is fixed in 3.0.4, 2.6.2.
  2. How severe is CVE-2026-22703? CVE-2026-22703 has a CVSS score of 5.5 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
  3. Which packages are affected by CVE-2026-22703?
    • github.com/sigstore/cosign/v3 (go) (versions <= 3.0.3)
    • github.com/sigstore/cosign/v2 (go) (versions <= 2.6.1)
  4. Is there a fix for CVE-2026-22703? Yes. CVE-2026-22703 is fixed in 3.0.4, 2.6.2. Upgrade to this version or later.
  5. Is CVE-2026-22703 exploitable, and should I be worried? Whether CVE-2026-22703 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
  6. What actually determines whether CVE-2026-22703 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
  7. How do I fix CVE-2026-22703?
    • Upgrade github.com/sigstore/cosign/v3 to 3.0.4 or later
    • Upgrade github.com/sigstore/cosign/v2 to 2.6.2 or later

Other vulnerabilities in github.com/sigstore/cosign/v3

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