# Activitypub-Federation has SSRF via 0.0.0.0 bypass in activitypub-federation-rust v4_is_invalid()

Advisory record · `GHSA-q537-8fr5-cw35`

- **Identifiers:** `GHSA-q537-8fr5-cw35` · `CVE-2026-33693`
- **State:** Confirmed
- **Severity:** CVSS 6.5 Medium
- **Critical:** No
- **Weakness (CWE):** [CWE-918](https://cwe.mitre.org/data/definitions/918.html)
- **Tags:** [Server-side request forgery (SSRF)](https://agentprime.io/advisories/tag/ssrf.md)
- **Published:** 25 Mar 2026
- **Updated:** 2 Apr 2026
- **Reviewed by a person:** No

Published by the GitHub Advisory Database at 25 Mar 2026, 20:23 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

## Affected packages

- `activitypub_federation` (crates.io): affected `<0.7.0-beta.9`; fixed in `0.7.0-beta.9`

## Machine-written summary

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

> The activitypub_federation crate before 0.7.0-beta.9 does not reject the unspecified address 0.0.0.0 (or its IPv4-mapped IPv6 form) in its SSRF protection, so requests to it are not blocked. A remote attacker who controls a domain can point that domain at 0.0.0.0 and have the library reach services listening on the target server's localhost, such as internal services. Upgrade to activitypub_federation 0.7.0-beta.9 or later. The source does not describe a workaround.

Written 8 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

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

- **CISA KEV:** Not listed.
- **EPSS:** 0.0038, the 32nd percentile, on 15 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

## Timeline

- 31 Oct 2026, 15:18 UTC: First seen by agentprime
- 31 Oct 2026, 15:18 UTC: [Confirmed by OSV](https://osv.dev/vulnerability/GHSA-q537-8fr5-cw35)

## Sources

- [GitHub Advisory Database: GHSA-q537-8fr5-cw35](https://github.com/advisories/GHSA-q537-8fr5-cw35)
- [OSV: GHSA-q537-8fr5-cw35](https://osv.dev/vulnerability/GHSA-q537-8fr5-cw35)
- <https://github.com/LemmyNet/lemmy/security/advisories/GHSA-q537-8fr5-cw35>
- <https://nvd.nist.gov/vuln/detail/CVE-2026-33693>
- <https://github.com/LemmyNet/activitypub-federation-rust/commit/4ae8532b17bc35755240b7f55d4a5b7665351599>
- <https://github.com/LemmyNet/activitypub-federation-rust>
- <https://github.com/advisories/GHSA-7723-35v7-qcxw>

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-q537-8fr5-cw35>, or `POST https://api.agentprime.io/v1/match` with your packages (<https://agentprime.io/api.md>)

---

The web page: <https://agentprime.io/advisories/GHSA-q537-8fr5-cw35/>. Everything for agents: <https://agentprime.io/llms.txt>.