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3.7
Cosign may accept expired intermediate certificates in some cases
CVE-2026-24122
GHSA-wfqv-66vq-46rm
Summary
A bug in Cosign can cause it to accept a signature from a certificate that has expired, but is still considered valid. This could happen if a company uses a custom certificate authority that issues certificates that are valid longer than their own certificate. To fix this, update to the latest Cosign version or verify the certificate chain separately. This issue is unlikely to affect users of the public Sigstore infrastructure.
What to do
- Update github.com sigstore to version 3.0.5.
Affected software
| Vendor | Product | Affected versions | Fix available |
|---|---|---|---|
| github.com | sigstore | <= 3.0.4 | 3.0.5 |
| sigstore | cosign | <= 3.0.5 | – |
Original title
Cosign considered signatures valid with expired intermediate certificates when transparency log verification is skipped
Original description
## Summary
When verifying artifact signatures using a certificate, Cosign first verifies the certificate chain using the leaf certificate's "not before" timestamp and later checks expiry of the leaf certificate using either a signed timestamp provided by the Rekor transparency log or from a timestamp authority, or using the current time. The root and all issuing certificates are assumed to be valid during the leaf certificate's validity. An issuing certificate with a validity that expires before the leaf certificate will be considered valid during verification even if the provided timestamp would mean the issuing certificate should be considered expired.
## Impact
No impact to users of the public Sigstore infrastructure. This may affect private deployments with customized PKIs. In practice, this is unlikely to occur as CAs should not be issuing certificates that outlive the validity of the CA and its parents.
## Workarounds
Upgrade to the latest release, or verify the certificate chain out of band.
## Example to Reproduce
* Root CA certificate is valid from 12pm-2pm
* Intermediate CA certificate is valid from 12:30pm-1:30pm
* Leaf certificate is valid from 1pm-3pm - **Note that this is unlikely to happen in practice**, as a CA shouldn't issue a certificate that would be valid after the issuing CA certificate expires
* Signature generated at 2:30pm with a signed timestamp
* During verification, the leaf certificate's not before time (1pm) is used to verify the chain - 1pm is in the validity windows for the root and intermediate CA certificates
* The timestamp's time is checked to be in the validity window of only the leaf certificate - 2:30pm is in the validity window for the leaf
* Even though the root and intermediate would be expired at 2:30pm, verification succeeds
When verifying artifact signatures using a certificate, Cosign first verifies the certificate chain using the leaf certificate's "not before" timestamp and later checks expiry of the leaf certificate using either a signed timestamp provided by the Rekor transparency log or from a timestamp authority, or using the current time. The root and all issuing certificates are assumed to be valid during the leaf certificate's validity. An issuing certificate with a validity that expires before the leaf certificate will be considered valid during verification even if the provided timestamp would mean the issuing certificate should be considered expired.
## Impact
No impact to users of the public Sigstore infrastructure. This may affect private deployments with customized PKIs. In practice, this is unlikely to occur as CAs should not be issuing certificates that outlive the validity of the CA and its parents.
## Workarounds
Upgrade to the latest release, or verify the certificate chain out of band.
## Example to Reproduce
* Root CA certificate is valid from 12pm-2pm
* Intermediate CA certificate is valid from 12:30pm-1:30pm
* Leaf certificate is valid from 1pm-3pm - **Note that this is unlikely to happen in practice**, as a CA shouldn't issue a certificate that would be valid after the issuing CA certificate expires
* Signature generated at 2:30pm with a signed timestamp
* During verification, the leaf certificate's not before time (1pm) is used to verify the chain - 1pm is in the validity windows for the root and intermediate CA certificates
* The timestamp's time is checked to be in the validity window of only the leaf certificate - 2:30pm is in the validity window for the leaf
* Even though the root and intermediate would be expired at 2:30pm, verification succeeds
nvd CVSS3.1
3.7
Vulnerability type
CWE-295
Improper Certificate Validation
- https://github.com/sigstore/cosign/commit/3c9a7363f563db76d78e2de2cabd945450f378... Patch
- https://github.com/sigstore/cosign/releases/tag/v3.0.5 Product Release Notes
- https://github.com/sigstore/cosign/security/advisories/GHSA-wfqv-66vq-46rm Exploit Vendor Advisory
- https://nvd.nist.gov/vuln/detail/CVE-2026-24122
- https://github.com/advisories/GHSA-wfqv-66vq-46rm
Published: 19 Feb 2026 · Updated: 11 Mar 2026 · First seen: 6 Mar 2026