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EUVD-2026-323666

fkie_cve-2026-44649

SillyTavern is a locally installed user interface that allows users to interact with text generation large language models, image generation engines, and text-to-speech voice models. Prior to 1.18.0, 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). This vulnerability is fixed in 1.18.0.

GHSA-gxx6-h3g6-vwjh — SillyTavern has Authentication Bypass via SSO Header Injection

Affected: npm: sillytavern

## 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`:

```js 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 (…