{"id":"CVE-2026-42180","aliases":["GHSA-3jvj-v6w2-h948"],"url":"https://o3.security/vulnerability/CVE-2026-42180","summary":"Lemmy: SSRF in /api/v3/post via Webmention dispatch","details":"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.","published":"2026-05-08T19:29:04.132Z","modified":"2026-08-07T11:51:05.308902424Z","cvss":{"score":6.3,"severity":"MEDIUM","vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:L"},"epss":null,"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"crates.io","name":"lemmy_api_common","fixedVersion":"0.19.18"}],"fix":null,"references":[{"type":"WEB","url":"https://github.com/LemmyNet/lemmy/releases/tag/0.19.18"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/42xxx/CVE-2026-42180.json"},{"type":"ADVISORY","url":"https://github.com/LemmyNet/lemmy/security/advisories/GHSA-3jvj-v6w2-h948"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-42180"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-07T11:51:05.308902424Z"}}