Attack Chain

1. An unauthenticated attacker identifies a vulnerable SillyTavern instance running version 1.17.0 or earlier.
2. The attacker crafts an HTTP POST request to the /api/extensions/delete endpoint (or /update, /version, /branches, /switch).
3. The attacker includes a JSON payload in the request body with the extensionName parameter set to ..
4. The application receives the request and proceeds to the src/endpoints/extensions.js file.
5. The application’s validation logic incorrectly allows the . value because the check !request.body.extensionName occurs before sanitization.
6. The sanitize-filename function converts the . to an empty string “”.
7. The path.join(basePath, "") function concatenates the base extensions path with the empty string, resulting in the basePath itself.
8. The application then executes fs.promises.rm(extensionPath, { recursive: true }), effectively deleting the entire extensions directory (e.g., data\default-user\extensions\).

Impact

Successful exploitation of this path traversal vulnerability (CVE-2026-44650) leads to the complete and unrecoverable removal of all installed third-party extensions from the SillyTavern instance. The default configuration of SillyTavern does not require authentication, making the vulnerability easily exploitable. If the application is configured with global: true and admin privileges, the attacker can also delete the global extensions directory, affecting all users. The vulnerability can be combined with CVE-2025-59159 (DNS rebinding) to enable unauthenticated remote exploitation from a malicious website. The CVSS score is 9.1 (Critical).

Recommendation

• Apply the suggested fix from the advisory to the /api/extensions/delete, /api/extensions/update, /api/extensions/version, /api/extensions/branches, and /api/extensions/switch endpoints, ensuring that validation occurs after sanitization and including a path traversal guard (see “Suggested Fix” in the content).
• Deploy the Sigma rule Detect SillyTavern Path Traversal Attempt via Extension Deletion to detect attempts to exploit CVE-2026-44650 targeting the /api/extensions/delete endpoint based on the extensionName parameter value.
• Deploy the Sigma rule Detect SillyTavern Path Traversal Attempt via Other Endpoints to detect attempts to exploit CVE-2026-44650 on the /api/extensions/update, /api/extensions/version, /api/extensions/branches, and /api/extensions/switch endpoints.
• Monitor web server logs for HTTP POST requests to the extensions API endpoints with suspicious extensionName values as an indicator of potential exploitation.