{
  "affected": [
    {
      "ranges": [
        {
          "database_specific": {
            "extracted_events": [
              {
                "introduced": "0"
              },
              {
                "fixed": "0.19.18"
              }
            ],
            "source": [
              "AFFECTED_FIELD",
              "REFERENCES"
            ]
          },
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "f32dd84d04541f8a94fee29d1f47f3f8eeaec0be"
            }
          ],
          "repo": "https://github.com/lemmynet/lemmy",
          "type": "GIT"
        }
      ]
    }
  ],
  "aliases": [
    "GHSA-3jvj-v6w2-h948"
  ],
  "database_specific": {
    "cna_assigner": "GitHub_M",
    "cwe_ids": [
      "CWE-918"
    ],
    "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/42xxx/CVE-2026-42180.json"
  },
  "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.",
  "id": "CVE-2026-42180",
  "modified": "2026-08-12T03:51:20.299713350Z",
  "published": "2026-05-08T19:29:04.132Z",
  "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"
    }
  ],
  "schema_version": "1.9.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:L",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Lemmy: SSRF in /api/v3/post via Webmention dispatch"
}