A vulnerability in the Clientless SSL VPN code could allow an unauthenticated, remote attacker to cause the reload of the affected system.
The vulnerability is due to improper handling of crafted HTTPS requests against the Cisco ASA Software configured for Clientless SSL VPN. An attacker could exploit this vulnerability by sending crafted HTTPS requests targeting the TCP port open for the Clientless SSL VPN feature.
Cisco has confirmed the vulnerability in a security advisory and released software updates.
Indicators of Compromise
Cisco Adaptive Security Appliance Software versions prior to 8.2(5.44), 8.3(2.39), 8.4(5.7), 8.6(1.12), 9.0(2.6), and 9.1(1.7) are vulnerable.
The vulnerability is due to improper handling of HTTPS requests that are processed as part of SSL VPN connections.
An unauthenticated, remote attacker could exploit this vulnerability by sending malicious HTTPS requests to the targeted device. The processing of the malicious requests could cause the device to reload, resulting in a DoS condition.
Attackers must send malicious HTTPS requests directly to the targeted device. Depending on device configuration, the attacker may require access to trusted networks or devices, limiting the potential for exploitation.
Administrators are advised to apply the appropriate updates.
Administrators may consider using IP-based access control lists (ACLs) to allow only trusted systems to access the affected systems.
Administrators are advised to monitor affected systems.
Cisco customers with active contracts can obtain updates through the Software Center at the following link: Cisco. Cisco customers without contracts can obtain upgrades by contacting the Cisco Technical Assistance Center at 1-800-553-2447 or 1-408-526-7209 or via email at firstname.lastname@example.org.
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Cisco Multivendor Vulnerability Alerts respond to vulnerabilities identified in third-party vendors' products. These alerts contain information compiled from diverse sources and provide comprehensive technical descriptions, objective analytical assessments, workarounds and practical safeguards, and links to vendor advisories and patches.