{"id":"CVE-2026-42180","sourceIdentifier":"security-advisories@github.com","published":"2026-05-08T20:16:31.023","lastModified":"2026-06-17T10:47:28.433","vulnStatus":"Deferred","cveTags":[],"descriptions":[{"lang":"en","value":"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."}],"affected":[{"source":"security-advisories@github.com","affectedData":[{"vendor":"LemmyNet","product":"lemmy","versions":[{"version":"< 0.19.18","status":"affected"}]}]}],"metrics":{"cvssMetricV31":[{"source":"security-advisories@github.com","type":"Secondary","cvssData":{"version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:L","baseScore":6.3,"baseSeverity":"MEDIUM","attackVector":"NETWORK","attackComplexity":"LOW","privilegesRequired":"LOW","userInteraction":"NONE","scope":"UNCHANGED","confidentialityImpact":"LOW","integrityImpact":"LOW","availabilityImpact":"LOW"},"exploitabilityScore":2.8,"impactScore":3.4}],"ssvcV203":[{"source":"134c704f-9b21-4f2e-91b3-4a467353bcc0","ssvcData":{"timestamp":"2026-05-13T17:17:59.971593Z","id":"CVE-2026-42180","options":[{"exploitation":"none"},{"automatable":"no"},{"technicalImpact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}}]},"weaknesses":[{"source":"security-advisories@github.com","type":"Secondary","description":[{"lang":"en","value":"CWE-918"}]}],"references":[{"url":"https://github.com/LemmyNet/lemmy/releases/tag/0.19.18","source":"security-advisories@github.com"},{"url":"https://github.com/LemmyNet/lemmy/security/advisories/GHSA-3jvj-v6w2-h948","source":"security-advisories@github.com"},{"url":"https://github.com/LemmyNet/lemmy/security/advisories/GHSA-3jvj-v6w2-h948","source":"134c704f-9b21-4f2e-91b3-4a467353bcc0"}]}