# SSRF protection bypass in safeurl via IPv6 addresses and unresolvable hosts

Advisory record · `EEF-CVE-2026-77866`

- **Identifiers:** `EEF-CVE-2026-77866` · `CVE-2026-77866`
- **State:** Confirmed
- **Severity:** CVSS 9.0 Critical
- **Critical:** Yes: CVSS 9+
- **Weakness (CWE):** [CWE-636](https://cwe.mitre.org/data/definitions/636.html) · [CWE-918](https://cwe.mitre.org/data/definitions/918.html)
- **Tags:** [Server-side request forgery (SSRF)](https://agentprime.io/advisories/tag/ssrf.md) · [CWE-636](https://agentprime.io/advisories/tag/cwe-636.md)
- **Published:** 15 Sept 2026
- **Updated:** 15 Sept 2026
- **Reviewed by a person:** No

Published by OSV at 15 Sept 2026, 15:38 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

## Critical

Critical, because:

- CVSS score 9.0: 9.0 or more.

How we decide what’s critical: <https://agentprime.io/advisories/critical.md>

## Affected packages

- `safeurl` (Hex): affected `>=0.1.0`; no fixed version yet

## 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

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

- **CISA KEV:** Not listed.
- **EPSS:** 0.0048, the 41st percentile, on 5 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

## Timeline

- 31 Oct 2026, 15:25 UTC: First seen by agentprime
- 31 Oct 2026, 15:25 UTC: [Confirmed by OSV](https://osv.dev/vulnerability/EEF-CVE-2026-77866)

## Sources

- [OSV: EEF-CVE-2026-77866](https://osv.dev/vulnerability/EEF-CVE-2026-77866)
- <https://cna.erlef.org/cves/CVE-2026-77866.html>
- <https://github.com/slab/safeurl-elixir/commit/feabbd0a13f83028ab24b71710526e9da9841f70>
- <https://hex.pm/packages/safeurl>

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/EEF-CVE-2026-77866>, 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/EEF-CVE-2026-77866/>. Everything for agents: <https://agentprime.io/llms.txt>.