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GHSA-xc4x-2452-5gc9

MediumCVSS 6.9 / 10
Published May 12, 2026·Last modified May 12, 2026
Affected Components(0)

No affected components available

Description

Resolution

Fixed in SillyTavern 1.18.0: a user-provided URL is no longer reflected in the HTTP response body.

Overview

  • Vulnerability Type: XSS
  • Affected Location: src/middleware/corsProxy.js:40
  • Trigger Scenario: reflected XSS in CORS proxy error response

Root Cause

When fetch(url) throws, the code sends: res.status(500).send('Error occurred while trying to proxy to: ' + url + ' ' + error). The url value is attacker-controlled (req.params.url) and is not HTML-escaped before rendering.

Source-to-Sink Chain

  1. Source (user-controlled input)
  • Entry point: GET /proxy/:url(*)
  1. Data flow
  • Code analysis shows concrete propagation into this sink:
    • vulnerability title: Reflected XSS in CORS proxy error response
    • sink location reached by attacker-controlled input: src/middleware/corsProxy.js:40
  • The same sink behavior is confirmed by controlled execution observations.
  1. Sink (dangerous operation)
  • Sink location: src/middleware/corsProxy.js:40
  • Vulnerable behavior: reflected XSS in CORS proxy error response

Exploitation Preconditions

  1. The attacker can inject controllable content into a rendered response.
  2. The vulnerable rendering context does not apply strict output encoding/sanitization.
  3. A victim user opens the affected page or response.

Risk

This issue enables script execution in the victim context and can compromise session or data integrity.

Impact

An attacker may run arbitrary JavaScript in the victim context, steal tokens, and manipulate user-visible behavior.

Remediation

  1. Never concatenate raw user input into HTML error responses.
  2. If URL echo is required, HTML-escape it or force plain-text output.
  3. Re-enable/strengthen CSP to reduce reflected injection impact.
Risk Scores
Base Score
6.9

The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker does not need any special privileges or access rights. No user interaction is needed for the attacker to exploit this vulnerability.

Threat Intelligence
2.7

Limited exploitation activity has been observed. Close monitoring and planned remediation are recommended.

EPSS
0.32%

The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.

Exploit
Not available

We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.

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Medium severity
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