Cisco ASA Adaptive Security Appliance (ASA) Software and Cisco ASA Services Module (ASASM) Software contain a vulnerability that could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition.
The vulnerability is due to insufficient validation of crafted authentication, authorization, and accounting (AAA) authentication challenges-responses. An unauthenticated, remote attacker could exploit this vulnerability by sending a crafted AAA authentication challenge-response to a Cisco ASA configured for SSL VPN. A successful exploit could allow the attacker to cause the targeted device to reload. Sustained attacks could result in a DoS condition.
Cisco has confirmed the vulnerability in a security advisory and released software updates.
Indicators of Compromise
Cisco ASA Software and Cisco ASASM Software Releases prior to 8.2(5.30) and 8.3(2.34) are vulnerable.
The vulnerability exists in the implementation of the AAA code for the remote SSL VPN (Clientless and AnyConnect) feature in the affected software. The vulnerability is due to insufficient validation of crafted authentication responses when a AAA challenge-response is required to complete the authentication process.
An unauthenticated, remote attacker could exploit this vulnerability by sending a crafted AAA authentication challenge-response to an ASA configured for SSL VPN. When affected software processes the malicious authentication challenge-response, an error condition could allow the attacker to cause the targeted device to reload. Sustained attacks could result in a DoS condition.
To exploit the vulnerability, the attacker must send malicious requests to the targeted system, likely requiring the attacker to have access to trusted internal networks. This access requirement limits the likelihood of a successful exploit.
Cisco ASA Software configured as an IPsec VPN Server, IPSEC/L2TP VPN Server, or IKEv2 AnyConnect server is not affected.
Cisco indicates through the CVSS score that functional exploit code exists; however, the code is not known to be publicly available.
Administrators are advised to apply the appropriate updates.
Administrators are advised to allow only trusted users to have network access.
Administrators may consider using IP-based access control lists (ACLs) to allow only trusted systems to access the affected systems.
Administrators can help protect affected systems from external attacks by using a solid firewall strategy.
Administrators are advised to monitor critical 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 e-mail 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.