Cosign's verify-blob-attestation reports false positive when payload parsing fails
Key facts
- Attack vector
- Network
- Privileges required
- None
- User interaction
- None
- Attack complexity
- Low
- Impact type
- —
- Confidentiality · integrity · availability
- None · Low · None
- Fix status
- Partial Red Hat: 7 without a fix
Attack profile from CVSS 3.1 · NVD. Fix status from CNA, GitHub and Red Hat.
Summary
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.
Why it matters now
SSVC decision points
CISA ADP · SSVC 2.0.3
- Exploitation
- None
- Automatable
- No
- Technical impact
- Partial
The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| sigstore | cosign | 3.0.0 to before 3.0.6; before 2.6.3 | 3.0.6, 2.6.3 | Patch available | CNA |
| — | github.com/sigstore/cosign (Go) | 3.0.0 to before 3.0.6 | 3.0.6 | Patch available | GHSA-w6c6-c85g-mmv6 |
| — | github.com/sigstore/cosign (Go) | before 2.6.3 | 2.6.3 | Patch available | GHSA-w6c6-c85g-mmv6 |
- cosign Vendorsigstore Affected 3.0.0 to before 3.0.6; before 2.6.3 Fixed in 3.0.6, 2.6.3 Patch available CNA
- github.com/sigstore/cosign (Go) Vendor— Affected 3.0.0 to before 3.0.6 Fixed in 3.0.6 Patch available GHSA-w6c6-c85g-mmv6
- github.com/sigstore/cosign (Go) Vendor— Affected before 2.6.3 Fixed in 2.6.3 Patch available GHSA-w6c6-c85g-mmv6
Remediation
- Fix · CNA cosign (sigstore) Fixed in 3.0.6, 2.6.3
- Fix · GHSA-w6c6-c85g-mmv6 github.com/sigstore/cosign (Go) Fixed in 3.0.6 Advisory →
- Fix · GHSA-w6c6-c85g-mmv6 github.com/sigstore/cosign (Go) Fixed in 2.6.3 Advisory →
Vendor assessments
Red Hat
Red Hat rating: Moderate. Red Hat's page for this CVE →
| Product | Status | Plan or fix |
|---|---|---|
| OpenShift Pipelines | Affected | No fix yet: Fix deferred |
| OpenShift Serverless | Affected | No fix yet: Fix deferred |
| Red Hat Advanced Cluster Security 4 | Affected | No fix yet: Fix deferred |
| Red Hat Trusted Artifact Signer | Affected | No fix yet: Fix deferred |
| Security Profiles Operator | Affected | No fix yet: Fix deferred |
| Zero Trust Workload Identity Manager | Affected | No fix yet: Fix deferred |
| Zero Trust Workload Identity Manager - Tech Preview | Affected | No fix yet: Fix deferred |
Timeline
- 2026-10-02 Threatist record created from CVE-2026-39395
- 2026-10-03 Alias added: GHSA-w6c6-c85g-mmv6
References
More sigstore Cosign vulnerabilities
- TI-2022-16356 False positive signature verification in cosign CVSS 3.1CRITICAL 9.8
- TI-2024-19670 Cosign vulnerable to machine-wide denial of service via malicious artifacts CVSS 3.1HIGH 7.5
- TI-2024-19669 Cosign vulnerable to system-wide denial of service via malicious attachments CVSS 3.1MEDIUM 5.9
- TI-2022-16479 Vulnerabilities with blob verification in sigstore cosign CVSS 3.1MEDIUM 5.5
- TI-2023-25220 Possible endless data attack from attacker-controlled registry in cosign CVSS 3.1MEDIUM 5.3
- TI-2026-18230 Cosign verification accepts any valid Rekor entry under certain conditions CVSS 3.1MEDIUM 5.5
Sources
- CVE-2026-39395 · CVE Program
- CVE-2026-39395 · NVD
- FIRST EPSS
- GHSA-w6c6-c85g-mmv6 · GitHub Advisory Database · CC BY 4.0
- CVE-2026-39395 · Red Hat security data · CC BY 4.0
This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences