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

Lemmy is a link aggregator and forum for the fediverse. Prior to version 0.7.0-beta.9, the v4isinvalid 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...