CVE-2001-0991 in Proxomitron Naoko-4
Summary
by MITRE
Cross-site scripting vulnerability in Proxomitron Naoko-4 BetaFour and earlier allows remote attackers to execute arbitrary script on other clients via an incorrect URL containing the malicious script, which is printed back in an error message.
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Analysis
by VulDB Data Team • 12/23/2024
The vulnerability identified as CVE-2001-0991 represents a classic cross-site scripting flaw in the Proxomitron web proxy software, specifically affecting versions Naoko-4 BetaFour and earlier. This security weakness resides in the application's handling of malformed URL inputs within its error message generation process. The flaw occurs when the proxy encounters an incorrectly formatted URL that triggers an error response, causing the system to display the malformed input directly in the error message without proper sanitization or encoding. This behavior creates an environment where malicious actors can inject arbitrary JavaScript code into URLs that are then processed by the proxy and subsequently rendered in error messages displayed to other users.
The technical implementation of this vulnerability stems from the software's inadequate input validation and output encoding mechanisms within its proxy error handling subsystem. When a client submits a malformed URL to the Proxomitron proxy, the application fails to properly escape or sanitize the input before incorporating it into error responses. This failure directly maps to CWE-79, which describes cross-site scripting vulnerabilities resulting from insufficient output escaping. The vulnerability operates through a typical XSS attack vector where an attacker crafts a malicious URL containing embedded JavaScript code, submits it to the vulnerable proxy, and waits for another user to access the error page where the malicious script executes in their browser context. The attack requires no authentication and can be executed remotely, making it particularly dangerous in shared network environments.
The operational impact of this vulnerability extends beyond simple script execution, as it enables attackers to perform various malicious activities including session hijacking, credential theft, and data exfiltration. When victims encounter the error message containing the injected script, their browsers execute the malicious code within the context of the proxy application, potentially allowing attackers to steal session cookies, redirect users to malicious sites, or manipulate the user interface of the proxy application itself. The vulnerability affects the confidentiality, integrity, and availability of the proxy service by creating potential attack vectors that could compromise user sessions and data. Given that Proxomitron operates as a web filtering and proxy tool, the attack surface is particularly concerning as it could allow attackers to bypass security controls or manipulate the filtering behavior of the system. This vulnerability aligns with ATT&CK technique T1566, which covers social engineering through malicious links, and T1059, which encompasses command and scripting interpreters.
Mitigation strategies for this vulnerability require immediate implementation of input validation and output encoding measures within the proxy's error handling components. The most effective approach involves sanitizing all user-supplied input before it is incorporated into error messages, utilizing proper HTML entity encoding for any dynamic content that might be rendered in the user interface. System administrators should update to versions of Proxomitron that have addressed this vulnerability, as the original affected versions contain no built-in protections against such attacks. Network administrators should also implement additional monitoring for suspicious URL patterns and consider deploying web application firewalls that can detect and block known XSS attack patterns. The vulnerability demonstrates the critical importance of proper input sanitization in proxy and filtering applications, as these systems often handle untrusted user input and must ensure that all dynamic content is properly escaped to prevent execution of malicious code in client browsers. Organizations using similar proxy systems should conduct comprehensive security assessments to identify and remediate similar input validation weaknesses in their web infrastructure components.