CVE-2026-42180

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

6.3CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:L

EPSS

0.2% chance of exploitation in the next 30 days; higher than 7% of CVEs (scores of 2026-10-26)

CWE

CWE-918

Published

2026-05-08

Modified

2026-10-26

Record from

the NVD, synced 2026-10-26

Packages (OSV)

References

• https://github.com/LemmyNet/lemmy/releases/tag/0.19.18
• https://github.com/LemmyNet/lemmy/security/advisories/GHSA-3jvj-v6w2-h948
• https://github.com/LemmyNet/lemmy/security/advisories/GHSA-3jvj-v6w2-h948

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