# Blocklist Bypass possible via ECDSA Signature Malleability

Advisory record · `GHSA-69x3-g4r3-p962`

- **Identifiers:** `GHSA-69x3-g4r3-p962` · `CVE-2026-25793` · `GO-2026-4458`
- **State:** Confirmed
- **Severity:** CVSS 7.6 High
- **Critical:** No
- **Weakness (CWE):** [CWE-347](https://cwe.mitre.org/data/definitions/347.html)
- **Tags:** [Weak cryptography or TLS](https://agentprime.io/advisories/tag/weak-crypto.md)
- **Published:** 6 Feb 2026
- **Updated:** 10 Sept 2026
- **Reviewed by a person:** No

Published by the GitHub Advisory Database at 6 Feb 2026, 20:05 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

## Affected packages

- `github.com/slackhq/nebula` (Go): affected `>=1.7.0, <1.10.3`; fixed in `1.10.3`

## Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

> Nebula versions 1.7.0 up to 1.10.3 (fixed in 1.10.3) are affected when P256 certificates are used. An attacker who holds the private key and certificate of a blocklisted host can use ECDSA signature malleability to produce a copy with a different fingerprint, evading the blocklist entry. Upgrade to Nebula 1.10.3. The source's workarounds are complex, so the practical alternative is rotating out CAs that signed blocklisted hosts.

Written 6 Nov 2026.

## 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

- 7.6 High, CVSS 4.0: `CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N`, from CNA (GitHub_M)

- **CISA KEV:** Not listed.
- **EPSS:** 0.0014, the 3rd percentile, on 14 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

## Timeline

- 31 Oct 2026, 14:43 UTC: First seen by agentprime
- 31 Oct 2026, 14:43 UTC: [Confirmed by OSV](https://osv.dev/vulnerability/GHSA-69x3-g4r3-p962)

## Sources

- [GitHub Advisory Database: GHSA-69x3-g4r3-p962](https://github.com/advisories/GHSA-69x3-g4r3-p962)
- [OSV: GHSA-69x3-g4r3-p962](https://osv.dev/vulnerability/GHSA-69x3-g4r3-p962)
- <https://github.com/slackhq/nebula/security/advisories/GHSA-69x3-g4r3-p962>
- <https://nvd.nist.gov/vuln/detail/CVE-2026-25793>
- <https://github.com/slackhq/nebula/commit/f573e8a26695278f9d71587390fbfe0d0933aa21>
- <https://github.com/slackhq/nebula>

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-69x3-g4r3-p962>, or `POST https://api.agentprime.io/v1/match` with your packages (<https://agentprime.io/api.md>)

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The web page: <https://agentprime.io/advisories/GHSA-69x3-g4r3-p962/>. Everything for agents: <https://agentprime.io/llms.txt>.