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Cosign's verify-blob-attestation reports false positive when payload parsing fails

Moderate severity GitHub Reviewed Published Apr 6, 2026 in sigstore/cosign • Updated Apr 8, 2026

Package

gomod github.com/sigstore/cosign (Go)

Affected versions

>= 3.0.0, < 3.0.6
< 2.6.3

Patched versions

3.0.6
2.6.3

Description

Description

cosign verify-blob-attestation may erroneously report a "Verified OK" result for attestations with malformed payloads or mismatched predicate types. For old-format bundles and detached signatures, this was due to a logic flaw in the error handling of the predicate type validation. For new-format bundles, the predicate type validation was bypassed completely.

Impact

When cosign verify-blob-attestation is used without --check-claims set to true, an attestation that has a valid signature but a malformed or unparsable payload would be incorrectly validated. Additionally, systems relying on --type <predicate type> to reject attestations with mismatched types would be lead to trust the unexpected attestation type.

Patches

v3.0.6, v2.6.3

Workarounds

Always set --check-claims=true for attestation verification.

References

@Hayden-IO Hayden-IO published to sigstore/cosign Apr 6, 2026
Published by the National Vulnerability Database Apr 7, 2026
Published to the GitHub Advisory Database Apr 8, 2026
Reviewed Apr 8, 2026
Last updated Apr 8, 2026

Severity

Moderate

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
Required
Scope
Unchanged
Confidentiality
None
Integrity
Low
Availability
None

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N

EPSS score

Exploit Prediction Scoring System (EPSS)

This score estimates the probability of this vulnerability being exploited within the next 30 days. Data provided by FIRST.
(11th percentile)

Weaknesses

Improper Check for Unusual or Exceptional Conditions

The product does not check or incorrectly checks for unusual or exceptional conditions that are not expected to occur frequently during day to day operation of the product. Learn more on MITRE.

CVE ID

CVE-2026-39395

GHSA ID

GHSA-w6c6-c85g-mmv6

Source code

Credits

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