SSRF in Lemmynet Lemmy

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.

Vulnerability class: SSRF (Server-Side Request Forgery)

Published · last modified .

CVSS v3 metric

CVSS v3 base score 6.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:L.

EPSS exploit prediction

EPSS: 0.003 (19.8th percentile), scored .

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 20th percentile — 19.8% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS trend (30 days)EPSS over the last 30 days for CVE-2026-42180: held from 0.002 to 0.003.

EPSS over last 30 days · oldest: 0.002 · newest: 0.003 · change: +0.001

Affected products

Weakness classification (CWE)

References

Frequently asked questions

What is CVE-2026-42180?
CVE-2026-42180 is a medium-severity vulnerability in Lemmynet Lemmy, classified under Server-Side Request Forgery (SSRF). CVSS score: 6.3/10. Published 2026-05-08.
How severe is CVE-2026-42180?
Medium severity. CVSS v3 base score is 6.3 out of 10.