CVE-2019-12677 in ASA
Summary
by MITRE
A vulnerability in the Secure Sockets Layer (SSL) VPN feature of Cisco Adaptive Security Appliance (ASA) Software could allow an authenticated, remote attacker to cause a denial of service (DoS) condition that prevents the creation of new SSL/Transport Layer Security (TLS) connections to an affected device. The vulnerability is due to incorrect handling of Base64-encoded strings. An attacker could exploit this vulnerability by opening many SSL VPN sessions to an affected device. The attacker would need to have valid user credentials on the affected device to exploit this vulnerability. A successful exploit could allow the attacker to overwrite a special system memory location, which will eventually result in memory allocation errors for new SSL/TLS sessions to the device, preventing successful establishment of these sessions. A reload of the device is required to recover from this condition. Established SSL/TLS connections to the device and SSL/TLS connections through the device are not affected. Note: Although this vulnerability is in the SSL VPN feature, successful exploitation of this vulnerability would affect all new SSL/TLS sessions to the device, including management sessions.
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Analysis
by VulDB Data Team • 12/29/2023
The vulnerability identified as CVE-2019-12677 affects Cisco Adaptive Security Appliance (ASA) Software and represents a significant denial of service risk within the SSL VPN functionality. This weakness resides in how the system processes Base64-encoded strings during SSL/TLS connection establishment, creating a pathway for authenticated remote attackers to disrupt normal operations. The flaw specifically manifests when the ASA software improperly handles certain Base64-encoded data structures, leading to memory corruption issues that ultimately prevent new SSL/TLS connections from being properly established. This vulnerability operates at the application layer and directly impacts the device's ability to maintain secure communication channels, making it particularly dangerous for network security infrastructure.
The technical mechanism behind this vulnerability stems from improper input validation and memory management within the SSL VPN processing pipeline. When an authenticated attacker establishes multiple SSL VPN sessions, the system's handling of Base64-encoded strings causes memory allocation errors that overwrite critical system memory locations. This memory corruption prevents the proper allocation of resources needed for new SSL/TLS connections, effectively creating a denial of service condition that affects the entire device's SSL/TLS capabilities. The vulnerability is classified under CWE-129 as an "Improper Validation of Array Index" and also relates to CWE-125 as "Out-of-bounds Read" since the system attempts to access memory locations beyond their allocated boundaries. The attack vector requires valid user credentials, making it an authenticated remote code execution risk rather than a purely network-based exploit.
The operational impact of CVE-2019-12677 extends beyond simple service disruption to potentially compromise the entire network security infrastructure managed by the affected ASA device. Since the vulnerability affects all new SSL/TLS sessions including management sessions, administrators may lose the ability to remotely access and manage the device, creating a critical operational vulnerability that could persist until a device reload occurs. This situation particularly affects enterprise environments where ASA devices serve as primary security gateways, potentially disrupting business continuity and network access for legitimate users. The attack scenario described in the vulnerability analysis aligns with ATT&CK technique T1499.004, which covers "Authorization Token Manipulation" and "Resource Hijacking" through denial of service attacks that target system resources.
Organizations should implement immediate mitigations including applying the latest security patches from Cisco, which address the memory handling issues in the SSL VPN processing module. Network segmentation strategies should be employed to limit the blast radius of potential exploitation, while monitoring systems should be configured to detect unusual patterns of SSL VPN session establishment that might indicate attempted exploitation. The vulnerability demonstrates the importance of proper input validation in security-critical applications and highlights the need for robust memory management practices in network infrastructure devices. Additionally, implementing multi-factor authentication and access control measures can reduce the risk of unauthorized access to the vulnerable SSL VPN feature, while regular security assessments should include testing for similar memory corruption vulnerabilities in network security appliances.