Medium 6.5Published Mar 26, 2026

CVE-2026-33693Lemmy's Activitypub-Federation has SSRF via 0.0.0.0 bypass in activitypub-federation-rust v4_is_invalid()

Updated under an hour ago (Oct 26, 2026, 1:20 PM ET)

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Exploited in the last 30 days

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.

CVSS: 6.5 MEDIUM (v3.1, CNA)CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
Weakness (CWE): CWE-918
Known exploited: Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days): Not loaded for this CVE
Assigned by: GitHub_M
NVD analysis: Deferred
Record last updated: Mar 30, 2026
First seen by InfoSec Signals: Oct 9, 2026

Affected products

Affected products

LemmyNet lemmy lemmynet:lemmy (from the name)	before 0.7.0-beta.9	CNA record

References

References

https://github.com/LemmyNet/lemmy/security/advisories/GHSA-q537-8fr5-cw35	x-refsource-confirm
https://github.com/LemmyNet/activitypub-federation-rust/commit/4ae8532b17bc35755240b7f55d4a5b7665351599	x-refsource-misc
https://github.com/advisories/GHSA-7723-35v7-qcxw	x-refsource-misc

The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.