GHSA-xw9q-2mv6-9fr8 Fedify has an incomplete SSRF mitigation after GHSA-p9cg-vqcc-grcx: validatePublicUrl allows special-use IPv4 ranges

• npm @fedify/fedify: >= 0.11.2, < 1.9.12 → fixed in 1.9.12 • npm @fedify/fedify: >= 1.10.0, < 1.10.11 → fixed in 1.10.11 • npm @fedify/fedify: >= 2.0.0, < 2.0.19 → fixed in 2.0.19 • npm @fedify/fedify: >= 2.1.0, < 2.1.15 → fixed in 2.1.15 • npm @fedify/fedify: >= 2.2.0, < 2.2.4 → fixed in 2.2.4 • npm @fedify/vocab-runtime: < 2.0.19 → fixed in 2.0.19 • npm @fedify/vocab-runtime: >= 2.1.0, < 2.1.15 → fixed in 2.1.15 • npm @fedify/vocab-runtime: >= 2.2.0, < 2.2.4 → fixed in 2.2.4

Summary 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 current IPv4 validation logic 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. I tested this against the current repository code at unreleased version 2.3.0. I used `>=0.11.2, = 16 && second = 16 && second " + isValidPublicIPv4Address(ip)); } ``` Observed output: ``` 8.8.8.8 => true 127.0.0.1 => false 10.0.0.1 => false 192.168.1.1 => false 169.254.169.254 => false 100.64.0.1 => true 198.18.0.1 => true 224.0.0.1 => true 240.0.0.1 => true 192.0.0.1 => true 192.0.2.1 => true 198.51.100.1 => true 203.0.113.1 => true ``` The validator correctly blocks some common private and local ranges, but incorrectly allows multiple special-use ranges. Examples of incorrectly allowed ranges Important examples include: ``` 100.64.0.0/10 Carrier-grade NAT 198.18.0.0/15 Benchmarking / internal testing networks 224.0.0.0/4 Multicast 240.0.0.0/4 Reserved 192.0.0.0/24 IETF protocol assignments ``` Additional correctness examples: ``` 192.0.2.0/24 Documentation range 198.51.100.0/24 Documentation range 203.0.113.0/24 Documentation range ``` Security Impact Any Fedify feature that accepts or processes remote ActivityPub object, activity, document, or media URLs and relies on validatePublicUrl() as an SSRF protection boundary may incorrectly allow outbound requests to special-use IPv4 destinations that should not be treated as public internet resources. This may allow an attacker-controlled ActivityPub object or media URL to cause a Fedify server to initiate requests to non-public or special-use network ranges, depending on the deployment environment and network routing. This is best understood as an incomplete fix/bypass class for the previous SSRF/internal-network-access advisory GHSA-p9cg-vqcc-grcx. Suggested Fix Avoid using a small manual denylist for public IP validation. Instead, validate that the resolved address is globally routable/public. At minimum, IPv4 validation should reject all relevant special-use ranges, including: ``` 0.0.0.0/8 10.0.0.0/8 100.64.0.0/10 127.0.0.0/8 169.254.0.0/16 172.16.0.0/12 192.0.0.0/24 192.0.2.0/24 192.168.0.0/16 198.18.0.0/15 198.51.100.0/24 203.0.113.0/24 224.0.0.0/4 240.0.0.0/4 ``` A safer long-term fix would be to use a maintained IP address classification library that explicitly supports security-sensitive public/global IP validation. Patch Idea ```ts export function isValidPublicIPv4Address(address: string): boolean { const parts = address.split(".").map((part) => parseInt(part, 10)); if ( parts.length !== 4 || parts.some((part) => Number.isNaN(part) || part 255) ) { return false; } const [a, b] = parts; if (a === 0) return false; if (a === 10) return false; if (a === 100 && b >= 64 && b = 16 && b = 224) return false; return true; } ``` Advisory Classification Note I understand this may be classified either as a new advisory or as an update/incomplete fix for GHSA-p9cg-vqcc-grcx. Since the issue appears to affect the validation logic added after the original SSRF fix, and because the affected code is part of the current security boundary for outbound URL fetching, I wanted to report it privately for maintainer review. Disclosure Note This report does not attempt to access any real internal network service. The proof focuses on the validation decision itself: multiple non-public or special-use IPv4 ranges are accepted as public by the current SSRF protection logic. Researcher Reported by Chaitanya Garware.