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CosignApplication · Sigstore

CVE-2026-39395

MEDIUM · 5.3 CVSS v3.1 Published 2026-04-07
Fix available
A fix is available. Upgrade to 2.6.3 / 3.0.6 or later.
See remediation →
62/100
Remediation priority · Elevated
Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
Cosign provides code signing and transparency for containers and binaries. Prior to 3.0.6 and 2.6.3, 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. This vulnerability is fixed in 3.0.6 and 2.6.3.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

Cosign's verify-blob-attestation function has a logic flaw in predicate type validation. For old-format bundles and detached signatures, error handling in the predicate type validation contains a logic flaw. For new-format bundles, the predicate type validation is bypassed entirely. This causes verification to incorrectly return 'Verified OK' for attestations with malformed payloads or mismatched predicate types.

MitigationUpgrade cosign to version 3.0.6 or 2.6.3 or later to receive the patch that corrects the predicate type validation logic.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
CosignApplication
Affected:< 2.6.3>= 3.0.0, < 3.0.6

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
Low
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Check installed cosign version
    Run `cosign version` or `cosign --version` and note the semantic version number
    Affected if The version is less than 2.6.3, or 3.0.0 and above but less than 3.0.6
  2. Identify use of verify-blob-attestation command
    Search codebase, scripts, CI pipelines, or cron jobs for the string `cosign verify-blob-attestation`
    Affected if The command is actively used in your environment
  3. Check for old-format bundles or detached signatures
    Review attestation files or configurations used with verify-blob-attestation for bundle format (old-format bundles typically have .sig or .att files)
    Affected if Attestations are provided as old-format bundles or detached signatures with this command
  4. Check for new-format bundles
    Review attestation files or configurations used with verify-blob-attestation for bundle format (new-format bundles typically have .json bundle files)
    Affected if Attestations are provided as new-format bundles with this command

You are affected if running a vulnerable cosign version (below 2.6.3 or 3.0.0-3.0.5) AND using verify-blob-attestation with any attestation bundle format.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 2.6.3 / 3.0.6 or later
Fixed in 2.6.33.0.6
Interim mitigation

Upgrade cosign to version 3.0.6 or 2.6.3 or later to receive the patch that corrects the predicate type validation logic.

Recommended fix High confidence

Cosign 2.6.3 (for 2.x users) or 3.0.6 (for 3.x users)

  1. 1. Identify your current cosign version by running `cosign version`
  2. 2. If you are using cosign 2.x (version < 2.6.3), upgrade to version 2.6.3
  3. 3. If you are using cosign 3.x (version >= 3.0.0 and < 3.0.6), upgrade to version 3.0.6
  4. 4. Download the updated cosign binary from the official releases (github.com/sigstore/cosign/releases)
  5. 5. Verify the upgrade was successful by running `cosign version` and confirming the version number matches the target fixed release
  6. 6. Re-run any `cosign verify-blob-attestation` commands that were previously used to confirm the fix is working correctly

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Cosign Scoped from the published advisory
  • Consultation1.0 h
  • Implementation1.0 h
  • Testing2.0 h
  • Review / QA1.0 h
5.0 hours of engineering $860
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-39395 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data