medium6.3
CVE-2026-42180
Lemmy is a link aggregator and forum for the fediverse.
Impact
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.
Affected packages
| Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|
| rust | lemmy_api_common | < 0.19.18 | 0.19.18 |
Weakness classification
References
- NVD record
- CVE.org record
- GitHub advisory
- https://github.com/advisories/GHSA-3jvj-v6w2-h948
- https://github.com/LemmyNet/lemmy/security/advisories/GHSA-3jvj-v6w2-h948
- https://github.com/LemmyNet/lemmy/commit/1f06693b708020c5c3a3752bd2f1c6006a75e9bc
- https://nvd.nist.gov/vuln/detail/CVE-2026-42180
- https://github.com/LemmyNet/lemmy/releases/tag/0.19.18