CVE-2026-33693

Summary

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 Software

Weaknesses

• CWE-918: CWE-918: Server-Side Request Forgery (SSRF)

ADP Enrichment

CISA ADP Vulnrichment

• SSVC:
• Exploitation: poc
  • Automatable: yes
  • Technical Impact: partial

References

• 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

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