🛡️ CVE-2026-42180
🟡 CVSS 6.3 — Medium ✅ No Known Exploit CWE-918 NVD
6.3
CVSS Score
0 Low4 Medium7 High9 Critical10

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.

Details

Severity Medium
CVSS Score 6.3
CVSS Vector CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:L
CWE CWE-918
Public Exploit ✅ No
Source NVD
Published 2026-04-24
Updated 2026-06-02
Modified 2026-05-13
Fix URL N/A

Affected Packages

Software From version Fixed in
lemmy-api-common — —
unknown — —

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