CVE-2026-50131: Fedify is a TypeScript library for building federated server apps powered by ActivityPub. Fedify previously addressed SSRF/internal network access in ...

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.

Metrics

CVSS 3.1

8.6/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:L

EPSS Probability

0.27%

18.5th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

References

Timeline

Published: Jun 10, 2026
Last Modified: Jun 17, 2026
Status: Deferred

Frequently Asked Questions

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.

How severe is CVE-2026-50131?

CVE-2026-50131 has a CVSS score of 8.6/10 (HIGH severity). The EPSS model estimates a 0.27% probability of exploitation in the next 30 days.

How do I fix CVE-2026-50131?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.