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VulnerabilityPublished Updated

CVE-2026-39395: V3 · Cosign's verify-blob-attestation reports false positive when payload parsing fails

Affects github.com/sigstore/cosign/v3Source GCVE Database

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Authoritative record:CVE-2026-39395· Medium 4.3

Not known to be exploited · CVSS 4.3 Medium : upgrade to 3.0.6 when convenient.

Data as of 12 Nov 2026, 19:19 UTC

CVSS 3.1 base score
4.3Medium
How severe the flaw is on the 0–10 CVSS scale.
Patch
Available – fixed in 3.0.6, 2.6.3
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 7 Apr 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 12 Nov 2026.

What to do

Upgrade github.com/sigstore/cosign/v3 to 3.0.6; github.com/sigstore/cosign/v2 to 2.6.3.

Affected software

ProductAffectedFixed in
Gogithub.com/sigstore/cosign/v3Affected
  • >=3.0.0 <3.0.6
Fixed in
  • 3.0.6
Gogithub.com/sigstore/cosign/v2Affected
  • <2.6.3
Fixed in
  • 2.6.3
Gogithub.com/sigstore/cosignAffected
  • <=1.13.6
Fixed in–

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

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

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