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NVD description
Fedify is a TypeScript library for building federated server apps powered by ActivityPub. Fedify previously addressed SSRF/internal network access in GHSA-p9cg-vqcc-grcx by adding public URL validation before runtime document and media fetching. However, the IPv4 validation logic present starting in version 0.11.2 and prior to versions 1.9.12, 1.10.11, 2.0.19, 2.1.15, and 2.2.4 appears incomplete. The `validatePublicUrl()` protection relies on `isValidPublicIPv4Address()` to reject non-public IPv4 destinations. The function blocks common private and local ranges such as `10.0.0.0/8`, `127.0.0.0/8`, `169.254.0.0/16`, `172.16.0.0/12`, and `192.168.0.0/16`, but it still treats several special-use, reserved, multicast, benchmarking, and carrier-grade NAT IPv4 ranges as valid public destinations. Because this validation is used as an SSRF defense before outbound fetches, this appears to be an incomplete mitigation or bypass class for the previous SSRF issue. Versions 1.9.12, 1.10.11, 2.0.19, 2.1.15, and 2.2.4 contain an updated patch.
Priority
LOW
Exploitation
NONE
PoC
NONE
Patch
AVAILABLE
Momentum
NONE
🚨 HIGH: CVE-2026-50131 (CVSS 8.6) - Fedify ActivityPub library SSRF bypass. Incomplete IPv4 validation allows access to reserved/special-use ranges. Patch immediately to v1.9.12+, 1.10.11+, 2.0.19+, 2.1.15+, or 2.2.4+ #CVE #PatchNow https://t.co/MG9Rc3Y7bp
Post summary
The tweet announces an SSRF bypass vulnerability in the Fedify ActivityPub library (CVSS 8.6) and urges users to apply specified patches immediately.