CVE-2026-42180
Lemmy: SSRF in /api/v3/post via Webmention dispatch
- State
- Published
- Severity
- 6.3 Medium
- Published
- May 8, 2026
- Updated
- May 13, 2026
- Reserved
- Apr 25, 2026
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.
Scores
| CVSS | Score | Vector | Source |
|---|---|---|---|
| 3.1 | 6.3 Medium | CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:L | GitHub_M |
Weaknesses
- CWE-918 Server-Side Request Forgery (SSRF)
Affected Products
| Product | Versions |
|---|---|
lemmyLemmyNet |
|
References
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