CVE-2013-6691 in ASA
Summary
by MITRE
The WebVPN CIFS implementation in Cisco Adaptive Security Appliance (ASA) Software 9.0(.4.1) and earlier allows remote CIFS servers to cause a denial of service (device reload) via a long share list, aka Bug ID CSCuj83344.
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Analysis
by VulDB Data Team • 02/08/2022
The vulnerability identified as CVE-2013-6691 affects Cisco Adaptive Security Appliance (ASA) software versions 9.0.4.1 and earlier, specifically within the WebVPN CIFS implementation. This flaw represents a critical denial of service condition that can be exploited by remote attackers to cause complete device reloads. The vulnerability manifests when remote CIFS servers provide excessively long share lists to the affected ASA devices, triggering an exploitable buffer condition that ultimately leads to system instability and complete restart of the security appliance.
The technical root cause of this vulnerability lies in insufficient input validation within the WebVPN CIFS functionality of the ASA software. When the device receives a CIFS share list that exceeds predetermined buffer limits, the system fails to properly handle the oversized data structure, resulting in memory corruption and subsequent device crash. This behavior aligns with CWE-121, which describes heap-based buffer overflow conditions, and CWE-122, which covers stack-based buffer overflows that can lead to arbitrary code execution or system crashes. The vulnerability is particularly concerning because it operates at the network level and can be triggered without authentication, making it accessible to remote attackers who can manipulate the CIFS share list parameters.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise network security infrastructure. When an ASA device experiences a reload due to this vulnerability, it creates a window of exposure where network traffic is not properly filtered or monitored, potentially allowing malicious actors to bypass security controls during the device restart period. The attack vector is particularly dangerous because it requires no credentials or prior access to the network, as the vulnerability can be exploited through remote CIFS server interactions. This makes the vulnerability particularly attractive to threat actors seeking to disrupt network operations or create cover for other attacks. The vulnerability's presence in WebVPN functionality also means that any organization relying on ASA devices for remote access services faces potential exposure, as the attack could be initiated through legitimate remote access sessions.
Organizations should implement immediate mitigations including applying the latest security patches from Cisco that address the buffer overflow condition in the WebVPN CIFS implementation. Network administrators should also consider disabling WebVPN CIFS functionality if it is not essential for business operations, as this provides an effective workaround while patches are deployed. Monitoring for unusual network traffic patterns or repeated connection attempts to CIFS shares that might indicate exploitation attempts should be implemented. The vulnerability's classification under the ATT&CK framework as a denial of service attack (T1499) highlights the need for organizations to maintain robust incident response procedures that can quickly identify and isolate affected systems. Additionally, implementing network segmentation and access controls can limit the potential impact of successful exploitation attempts by reducing the attack surface available to remote adversaries.