CVE-2026-42180mediumCWE-918

CVE-2026-42180: medium-severity vulnerability in LemmyNet lemmy

Lemmy: SSRF in /api/v3/post via Webmention dispatch

Published · Updated

Follow this CVE+ Monitor lemmy+ Monitor lemmy_api_common

E-mail alert when it lands in KEV, gets a public PoC or its score goes up.

13Vexday Risk Score

No sign of exploitation. No public exploitation artifact known so far.

ssvc Trackcvss 6.3epss 0.2%
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.
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:L
Affected products
LemmyNet · lemmy
Related CVEs — LemmyNet lemmy

In the same product, most dangerous first.

CVE-2026-54739MEDIUMLemmy: Login Endpoint User Enumeration via HTTP Response Code DifferentialEPSS 0.6%CVE-2026-54738MEDIUMLemmy: Rate limit bypass via X-Forwarded-For header spoofing in actix-web ConnectionInfoEPSS 0.6%CVE-2026-54742MEDIUMLemmy: `CollectionAdd::Featured` does not check the post is in the communityEPSS 0.5%CVE-2026-54743MEDIUMLemmy: Stored XSS via markdown image alt-text in lemmy-ui html5-embedEPSS 0.5%CVE-2024-23649HIGHAny authenticated user may obtain private message details from other users on the same instanceEPSS 0.5%CVE-2026-54741MEDIUMLemmy: Blocked users can edit private messages sent before the blockEPSS 0.5%