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

Advisory record · `GHSA-w6c6-c85g-mmv6`

- **Identifiers:** `GHSA-w6c6-c85g-mmv6` · `BIT-cosign-2026-39395` · `CVE-2026-39395` · `GO-2026-5694`
- **State:** Confirmed
- **Severity:** CVSS 4.3 Medium
- **Critical:** No
- **Weakness (CWE):** [CWE-754](https://cwe.mitre.org/data/definitions/754.html)
- **Tags:** [CWE-754](https://agentprime.io/advisories/tag/cwe-754.md)
- **Published:** 8 Apr 2026
- **Updated:** 10 Sept 2026
- **Reviewed by a person:** No

Published by the GitHub Advisory Database at 8 Apr 2026, 00:15 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

## Affected packages

- `github.com/sigstore/cosign` (Go): affected `>=3.0.0, <3.0.6 || <2.6.3`; fixed in `3.0.6`, `2.6.3`

## Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

## Severity and exploitation

- 4.3 Medium, CVSS 3.1: `CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N`, from CNA (GitHub_M)

- **CISA KEV:** Not listed.
- **EPSS:** 0.0025, the 16th percentile, on 6 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

## Timeline

- 31 Oct 2026, 14:13 UTC: First seen by agentprime
- 31 Oct 2026, 14:13 UTC: [Confirmed by OSV](https://osv.dev/vulnerability/GHSA-w6c6-c85g-mmv6)

## Sources

- [GitHub Advisory Database: GHSA-w6c6-c85g-mmv6](https://github.com/advisories/GHSA-w6c6-c85g-mmv6)
- [OSV: GHSA-w6c6-c85g-mmv6](https://osv.dev/vulnerability/GHSA-w6c6-c85g-mmv6)
- <https://github.com/sigstore/cosign/security/advisories/GHSA-w6c6-c85g-mmv6>
- <https://nvd.nist.gov/vuln/detail/CVE-2026-39395>
- <https://github.com/sigstore/cosign>

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.

## Check whether this affects you

A Match means an installed version is in the affected range above. Most don’t affect the app; agentprime hasn’t analysed this one yet.

- With the agentprime MCP server (<https://api.agentprime.io/mcp>), ask your agent to check the project: `check_lockfile` sends a lockfile, `check_packages` a list of installed packages, and both return the Matches and the upgrades that clear them. `get_advisory` returns this record. Setup: <https://agentprime.io/mcp.md>
- In a browser: <https://agentprime.io/check/> reads your lockfile in the browser, never uploading it.
- Whether it touches your code, with file and line: the Claude Code plugin, <https://agentprime.io/plugin.md>
- As JSON: <https://api.agentprime.io/v1/advisories/GHSA-w6c6-c85g-mmv6>, or `POST https://api.agentprime.io/v1/match` with your packages (<https://agentprime.io/api.md>)

---

The web page: <https://agentprime.io/advisories/GHSA-w6c6-c85g-mmv6/>. Everything for agents: <https://agentprime.io/llms.txt>.