CVE-2016-6436 in HostScan Engine
Summary
by MITRE
Cross-site scripting (XSS) vulnerability in HostScan Engine 3.0.08062 through 3.1.14018 in the Cisco Host Scan package, as used in ASA Web VPN, allows remote attackers to inject arbitrary web script or HTML via a crafted URL, aka Bug ID CSCuz14682.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 05/04/2019
The vulnerability CVE-2016-6436 represents a critical cross-site scripting flaw in Cisco Host Scan Engine versions 3.0.08062 through 3.1.14018, which are integral components of Cisco Adaptive Security Appliance Web VPN implementations. This vulnerability exists within the Host Scan functionality that is responsible for performing endpoint security checks and validation before granting network access through the ASA Web VPN service. The flaw specifically manifests when the Host Scan engine processes user-supplied input through crafted URLs, creating an avenue for malicious actors to execute arbitrary web scripts or HTML code within the context of authenticated users' browsers. The vulnerability is categorized under CWE-79 as a classic cross-site scripting weakness, where insufficient input validation and output encoding allow attacker-controlled data to be interpreted as executable code by web browsers.
The technical exploitation of this vulnerability occurs when remote attackers craft malicious URLs that contain malicious payloads designed to exploit the insufficient sanitization of input parameters within the Host Scan engine. These crafted URLs can be delivered through various attack vectors including phishing campaigns, compromised web resources, or social engineering tactics. When authenticated users navigate to these malicious URLs within the context of their Web VPN session, the malicious code executes in their browser, potentially leading to session hijacking, credential theft, or unauthorized access to network resources. The vulnerability specifically affects the processing of URL parameters that are not properly validated or escaped before being rendered in the web interface, creating a persistent XSS condition that can be leveraged for extended attack campaigns.
The operational impact of CVE-2016-6436 extends beyond simple script execution, as it compromises the fundamental security model of the Cisco ASA Web VPN implementation. Attackers can leverage this vulnerability to establish persistent access to network resources, steal user sessions, and potentially escalate privileges within the network environment. The vulnerability affects organizations that rely on Cisco ASA Web VPN for remote access, making it particularly dangerous for enterprises with distributed workforces and remote users. The flaw undermines the trust model of the Web VPN system, as authenticated users become potential vectors for lateral movement and data exfiltration. This vulnerability directly impacts the CIA triad, specifically compromising confidentiality and integrity by allowing unauthorized code execution and data manipulation within user sessions.
Organizations should implement immediate mitigations including applying the latest security patches from Cisco, which address the input validation flaws in the Host Scan engine. Network administrators should also consider implementing additional security controls such as web application firewalls that can detect and block malicious XSS payloads, enhanced monitoring of Web VPN traffic for suspicious URL patterns, and regular security assessments of the ASA Web VPN configuration. The vulnerability aligns with ATT&CK technique T1059.007 for script execution and T1566 for phishing campaigns, making it a significant concern for organizations following the MITRE ATT&CK framework. Additionally, implementing proper input validation and output encoding practices in web applications, as recommended by OWASP, can help prevent similar vulnerabilities in other systems. Organizations should also conduct thorough security awareness training for users to recognize and avoid potentially malicious URLs that could exploit this vulnerability during Web VPN sessions.