CVE-2006-3073 in WebVPN
Summary
by MITRE
Multiple cross-site scripting (XSS) vulnerabilities in the WebVPN feature in the Cisco VPN 3000 Series Concentrators and Cisco ASA 5500 Series Adaptive Security Appliances (ASA), when in WebVPN clientless mode, allow remote attackers to inject arbitrary web script or HTML via the domain parameter in (1) dnserror.html and (2) connecterror.html, aka bugid CSCsd81095 (VPN3k) and CSCse48193 (ASA). NOTE: the vendor states that "WebVPN full-network-access mode" is not affected, despite the claims by the original researcher.
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Analysis
by VulDB Data Team • 06/20/2019
The vulnerability described in CVE-2006-3073 represents a critical cross-site scripting flaw affecting Cisco's WebVPN implementation across multiple security appliances including the VPN 3000 Series Concentrators and ASA 5500 Series Adaptive Security Appliances. This weakness specifically manifests when these devices operate in WebVPN clientless mode, creating a dangerous attack surface that could be exploited by remote adversaries to execute malicious code within the context of affected users' browsers. The vulnerability is categorized under CWE-79 as a failure to sanitize input data, which directly enables malicious script injection attacks that bypass standard security controls.
The technical exploitation occurs through manipulation of the domain parameter within two specific error handling pages: dnserror.html and connecterror.html. Attackers can craft malicious payloads that get executed when these error pages are rendered to users, allowing them to inject arbitrary web scripts or HTML content. The vulnerability affects both the VPN3000 series and ASA devices, with distinct bug identifiers CSCsd81095 for the VPN3000 and CSCse48193 for the ASA, indicating separate but related code paths in the respective implementations. These error pages serve as entry points where user-supplied input is not properly validated or escaped, creating opportunities for attackers to establish persistent malicious web sessions.
The operational impact of this vulnerability extends beyond simple script execution, as it enables attackers to perform session hijacking, steal sensitive authentication tokens, redirect users to malicious sites, or even deliver additional malware payloads. When users encounter DNS or connection errors while using WebVPN clientless mode, they are presented with these vulnerable error pages, making the attack surface particularly dangerous as it leverages legitimate error conditions to deliver malicious content. The vulnerability affects the core authentication and session management functionality of these appliances, potentially allowing unauthorized access to corporate networks and sensitive data. According to the ATT&CK framework, this represents a technique categorized under T1566 (Phishing) and T1059 (Command and Scripting Interpreter) as attackers can leverage the XSS to establish persistent access and execute commands within the browser context.
Cisco's vendor statement clarifying that "WebVPN full-network-access mode" remains unaffected provides important operational context for security teams, indicating that the vulnerability is specifically tied to clientless browsing functionality rather than the complete WebVPN implementation. This distinction allows organizations to maintain secure access through full-network mode while addressing the specific clientless mode issue. Organizations should implement immediate mitigations including input validation for error pages, output encoding of user-supplied parameters, and network segmentation to limit exposure. The vulnerability highlights the importance of proper input sanitization and the need for comprehensive security testing of error handling components, particularly in network infrastructure devices where user interaction occurs. Security teams should also consider implementing web application firewalls to detect and prevent exploitation attempts targeting these specific error page vulnerabilities.