CVE-2026-44651: Sillytavern Cross-Site Scripting Vulnerability

MODERATE
Advisory Identifier: GHSA-xc4x-2452-5gc9
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CWE-79
Published
Advisory Summary

CVE-2026-44651 is a MODERATE cross-site scripting vulnerability (CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')) affecting Sillytavern libraries in the npm ecosystem. The issue involves sillytavern has a reflected xss vulnerability in the cors proxy middleware. Remediation is available by upgrading affected packages to version 1.18.0.

CVE-2026-44651 at a Glance

CVE Identifier CVE-2026-44651
GHSA Identifier GHSA-xc4x-2452-5gc9
Severity MODERATE
CVSS v3.1 Base Score N/A
CWE Classification CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
Affected Product Sillytavern
Package Ecosystem npm
Published Date
Last Updated

How to Fix CVE-2026-44651

To remediate this vulnerability, upgrade all affected Sillytavern dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

sillytavern fixed: 1.18.0 
npm install sillytavern@1.18.0
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

npm ls sillytavern

How to Check if You Are Affected

To determine whether your Node.js application is affected by CVE-2026-44651, inspect your project dependencies using npm:

npm ls sillytavern

Analyze the terminal output to locate any version of Sillytavern in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 1.18.0), your application is affected.

Note: The npm ls sillytavern command inspects dependencies declared in your package.json and lockfile; it does not perform automated runtime dynamic scanning.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting'), where the product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users. In Sillytavern, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

## 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 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.

CVE-2026-44651 Affected Sillytavern Versions

1 component(s)
Fixed Versions:
1.18.0
Product / Package Ecosystem Affected Versions Fixed Version
sillytavern
npm/sillytavern
npm
< 1.18.0
1.18.0

References

GitHub Advisory / Wiki ADVISORY
https://github.com/SillyTavern/SillyTavern/security/advisories/GHSA-xc4x-2452-5gc9
NVD — CVE-2026-44651 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-44651
Sillytavern Source Repository REPOSITORY
https://github.com/SillyTavern/SillyTavern
Sillytavern Release RELEASE
https://github.com/SillyTavern/SillyTavern/releases/tag/1.18.0

Frequently Asked Questions

What is CVE-2026-44651?
CVE-2026-44651 is a security vulnerability in Sillytavern involving SillyTavern has a reflected XSS vulnerability in the CORS proxy middleware under CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting').
Which Sillytavern versions are affected?
Affected versions include releases prior to 1.18.0 across affected packages: sillytavern.
What version fixes CVE-2026-44651?
Upgrading to 1.18.0 (or the latest patched release for your respective branch) resolves the vulnerability.
Is sillytavern affected?
Yes, sillytavern is affected in releases prior to 1.18.0. Upgrade your dependency to 1.18.0 or later.
What CWE is associated with CVE-2026-44651?
CVE-2026-44651 is classified under CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') (The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.).
How can I check npm dependencies for CVE-2026-44651?
Run the dependency tree command: 'npm ls sillytavern'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-xc4x-2452-5gc9",
  "modified" : "2026-06-09T10:32:13Z",
  "published" : "2026-05-12T22:23:56Z",
  "aliases" : [ "CVE-2026-44651" ],
  "summary" : "SillyTavern has a reflected XSS vulnerability in the CORS proxy middleware",
  "details" : "## Resolution\n\nFixed in SillyTavern 1.18.0: a user-provided URL is no longer reflected in the HTTP response body.\n\n## Overview\n- Vulnerability Type: XSS\n- Affected Location: `src/middleware/corsProxy.js:40`\n- Trigger Scenario: reflected XSS in CORS proxy error response\n\n## Root Cause\nWhen `fetch(url)` throws, the code sends:\n`res.status(500).send('Error occurred while trying to proxy to: ' + url + ' ' + error)`.\nThe `url` value is attacker-controlled (`req.params.url`) and is not HTML-escaped before rendering.\n\n## Source-to-Sink Chain\n1. Source (user-controlled input)\n- Entry point: `GET /proxy/:url(*)`\n\n2. Data flow\n- Code analysis shows concrete propagation into this sink:\n  - vulnerability title: `Reflected XSS in CORS proxy error response`\n  - sink location reached by attacker-controlled input: `src/middleware/corsProxy.js:40`\n- The same sink behavior is confirmed by controlled execution observations.\n\n3. Sink (dangerous operation)\n- Sink location: `src/middleware/corsProxy.js:40`\n- Vulnerable behavior: reflected XSS in CORS proxy error response\n\n## Exploitation Preconditions\n1. The attacker can inject controllable content into a rendered response.\n2. The vulnerable rendering context does not apply strict output encoding/sanitization.\n3. A victim user opens the affected page or response.\n\n## Risk\nThis issue enables script execution in the victim context and can compromise session or data integrity.\n\n## Impact\nAn attacker may run arbitrary JavaScript in the victim context, steal tokens, and manipulate user-visible behavior.\n\n## Remediation\n1. Never concatenate raw user input into HTML error responses.\n2. If URL echo is required, HTML-escape it or force plain-text output.\n3. Re-enable/strengthen CSP to reduce reflected injection impact.",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "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"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "sillytavern"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "1.18.0"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 1.17.0"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/SillyTavern/SillyTavern/security/advisories/GHSA-xc4x-2452-5gc9"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-44651"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/SillyTavern/SillyTavern"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/SillyTavern/SillyTavern/releases/tag/1.18.0"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-79" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-05-12T22:23:56Z",
    "nvd_published_at" : "2026-05-29T19:16:24Z"
  }
}