Description
Lemmy is a link aggregator and forum for the fediverse. Prior to version 0.19.18, Lemmy allows an authenticated low-privileged user to create a link post through POST /api/v3/post. When a post is created in a public community, the backend asynchronously sends a Webmention to the attacker-controlled link target. The submitted URL is checked for syntax and scheme, but the audited code path does not reject loopback, private, or link-local destinations before the Webmention request is issued. This lets a normal user trigger server-side HTTP requests toward internal services. This issue has been patched in version 0.19.18.
Problem types
CWE-918: Server-Side Request Forgery (SSRF)
Product status
References
github.com/.../lemmy/security/advisories/GHSA-3jvj-v6w2-h948
github.com/LemmyNet/lemmy/releases/tag/0.19.18