medium6.5
CVE-2026-33693
Activitypub-Federation has SSRF via 0.0.0.0 bypass in activitypub-federation-rust v4_is_invalid()
Impact
Lemmy is a link aggregator and forum for the fediverse. Prior to version 0.7.0-beta.9, the `v4_is_invalid()` function in `activitypub-federation-rust` (`src/utils.rs`) does not check for `Ipv4Addr::UNSPECIFIED` (0.0.0.0). An unauthenticated attacker controlling a remote domain can point it to 0.0.0.0, bypass the SSRF protection introduced by the fix for CVE-2025-25194 (GHSA-7723-35v7-qcxw), and reach localhost services on the target server. Version 0.7.0-beta.9 patches the issue.
Affected packages
| Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|
| rust | activitypub_federation | < 0.7.0-beta.9 | 0.7.0-beta.9 |
Weakness classification
References
- NVD record
- CVE.org record
- GitHub advisory
- https://github.com/advisories/GHSA-q537-8fr5-cw35
- https://github.com/LemmyNet/lemmy/security/advisories/GHSA-q537-8fr5-cw35
- https://github.com/LemmyNet/activitypub-federation-rust/commit/4ae8532b17bc35755240b7f55d4a5b7665351599
- https://github.com/advisories/GHSA-7723-35v7-qcxw
- https://nvd.nist.gov/vuln/detail/CVE-2026-33693