CVE-2025-41355 Overview
A Reflected Cross-Site Scripting (XSS) vulnerability has been identified in Anon Proxy Server v0.104. This security flaw allows an attacker to execute arbitrary JavaScript code in a victim's browser by crafting and distributing a malicious URL. The vulnerability specifically affects the port and proxyPort parameters in the /anon.php endpoint, enabling attackers to steal sensitive user data such as session cookies or perform unauthorized actions on behalf of the authenticated user.
Critical Impact
Attackers can exploit this XSS vulnerability to hijack user sessions, steal authentication credentials, and execute malicious scripts in the context of legitimate user sessions.
Affected Products
- Anon Proxy Server v0.104
Discovery Timeline
- 2026-03-31 - CVE CVE-2025-41355 published to NVD
- 2026-04-01 - Last updated in NVD database
Technical Details for CVE-2025-41355
Vulnerability Analysis
This Reflected XSS vulnerability (CWE-79) occurs when user-supplied input through the port and proxyPort parameters is reflected back to the browser without proper sanitization or encoding. When a victim clicks on a specially crafted malicious link, the injected JavaScript payload executes within the security context of the vulnerable web application. This allows attackers to access the Document Object Model (DOM), manipulate page content, and interact with the application as if they were the legitimate user.
The network-accessible nature of this vulnerability means attackers can distribute malicious links through phishing emails, social media, or other communication channels to reach potential victims remotely.
Root Cause
The vulnerability stems from insufficient input validation and output encoding in the /anon.php endpoint. The port and proxyPort parameters do not properly sanitize or escape user-controlled input before including it in the HTTP response. This failure to implement proper input validation allows malicious script content to be injected and subsequently executed by the victim's browser.
Attack Vector
The attack requires user interaction where a victim must click on a malicious URL containing the XSS payload. An attacker constructs a URL targeting the /anon.php endpoint with JavaScript code embedded in either the port or proxyPort parameters. When the victim accesses this link, the server reflects the malicious input back in the response, and the browser executes the injected script. This can be leveraged to exfiltrate session tokens, redirect users to phishing sites, or perform actions within the application using the victim's authenticated session.
The vulnerability can be exploited by injecting script tags or JavaScript event handlers into the vulnerable parameters. For example, an attacker might craft a URL containing <script> tags or event handlers like onload or onerror that execute when the page renders. For detailed technical information, see the INCIBE Security Notice.
Detection Methods for CVE-2025-41355
Indicators of Compromise
- Suspicious HTTP requests to /anon.php containing encoded JavaScript payloads or <script> tags in URL parameters
- Unusual values in port or proxyPort parameters that contain HTML special characters such as <, >, ", or '
- Server logs showing requests with URL-encoded script content targeting the vulnerable endpoint
Detection Strategies
- Implement Web Application Firewall (WAF) rules to detect and block XSS payloads in HTTP requests
- Monitor web server access logs for requests containing common XSS patterns such as <script>, javascript:, or onerror=
- Deploy browser-based Content Security Policy (CSP) violation reporting to identify attempted XSS attacks
Monitoring Recommendations
- Enable detailed logging on web servers to capture full request URLs including query string parameters
- Configure SIEM rules to alert on multiple requests to /anon.php with unusual or encoded parameter values
- Implement real-time monitoring for CSP violations that may indicate XSS exploitation attempts
How to Mitigate CVE-2025-41355
Immediate Actions Required
- Restrict access to the Anon Proxy Server administrative interface from untrusted networks
- Implement a Content Security Policy (CSP) header to prevent execution of inline scripts
- Deploy a Web Application Firewall with XSS detection rules to filter malicious requests
- Educate users about the risks of clicking on suspicious or unfamiliar links
Patch Information
No official patch information is currently available from the vendor. Organizations should monitor the INCIBE Security Notice for updates regarding remediation options. Consider upgrading to a newer version when available or implementing compensating controls.
Workarounds
- Implement server-side input validation to reject or sanitize special characters in the port and proxyPort parameters
- Apply output encoding to ensure user-supplied data is HTML-encoded before being rendered in responses
- Configure strict Content Security Policy headers to block inline script execution
# Example Apache configuration to add Content Security Policy header
<IfModule mod_headers.c>
Header set Content-Security-Policy "default-src 'self'; script-src 'self'; style-src 'self' 'unsafe-inline'"
</IfModule>
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
