Fedify has an incomplete SSRF mitigation after GHSA-p9cg-vqcc-grcx: validatePublicUrl allows special-use IPv4 ranges
CVE-2026-50131
What is CVE-2026-50131?
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.
Affected Version(s)
fedify >= 0.11.2, < 1.9.12 < 0.11.2, 1.9.12
fedify >= 1.10.0, < 1.10.11 < 1.10.0, 1.10.11
fedify >= 2.0.0, < 2.0.19 < 2.0.0, 2.0.19