SillyTavern has a reflected XSS vulnerability in the CORS proxy middleware

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

6.9 · CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N · score source

EPSS

• CVE-2026-44651: 0.32% estimated exploitation activity in the next 30 days; percentile 25.40 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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() 2. 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. 3. Sink (dangerous operation) - Sink location: src/middleware/corsProxy.js:40 - Vulnerable behavior: reflected XSS in…

Published by the source

12 May 2026, 22:23 UTC

Last modified by the source

9 Jun 2026, 10:45 UTC

Source last checked

26 Oct 2026, 12:53 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-xc4x-2452-5gc9

2. Revision 2 · amended · 25 Oct 2026

   Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

3. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-xc4x-2452-5gc9

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# Patch Next advisory brief: CVE-2026-44651

Advisory: SillyTavern has a reflected XSS vulnerability in the CORS proxy middleware
IDs: CVE-2026-44651, GHSA-xc4x-2452-5gc9
Record: https://patchnext.com/advisories/cve-2026-44651 (revision 3, source checked 26 Oct 2026, 12:53 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.9)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: sillytavern 1.18.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm sillytavern: affected <= 1.17.0; fixed in 1.18.0

## Suggested inspection (read-only)
- `npm ls sillytavern --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on sillytavern.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-xc4x-2452-5gc9 (OSV record GHSA-xc4x-2452-5gc9 lists affected ranges: npm sillytavern >=0 <1.18.0 (fixed))
- Verified: https://github.com/advisories/GHSA-xc4x-2452-5gc9 (GitHub-reviewed advisory GHSA-xc4x-2452-5gc9 lists affected ranges: npm sillytavern >=0 <=1.17.0)

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