CVE-2013-7098 in OpenConnect
Summary
by MITRE
OpenConnect VPN client with GnuTLS before 5.02 contains a heap overflow if MTU is increased on reconnection.
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Analysis
by VulDB Data Team • 04/22/2023
The vulnerability CVE-2013-7098 represents a critical heap overflow condition affecting the OpenConnect VPN client when utilizing GnuTLS versions prior to 5.02. This flaw manifests specifically during reconnection scenarios where the Maximum Transmission Unit (MTU) is increased, creating a dangerous memory corruption state that can be exploited by remote attackers. The issue stems from inadequate input validation and memory management within the client's reconnection handling logic, where the system fails to properly bounds-check data when processing MTU adjustments. This vulnerability falls under the CWE-121 heap-based buffer overflow category, which is classified as a serious memory safety issue that can lead to arbitrary code execution or system compromise. The OpenConnect client, widely deployed for secure remote access solutions, becomes susceptible to this attack vector when operating in environments where reconnection with modified MTU values occurs.
The technical implementation of this vulnerability involves the client's handling of network packet sizes during reconnection sequences. When the MTU value is increased during reconnection, the application allocates memory buffers based on the new size without proper validation of the input parameters. The GnuTLS library's interaction with the OpenConnect client creates a scenario where memory corruption occurs in the heap allocation region, potentially allowing attackers to overwrite adjacent memory locations. This flaw operates at the intersection of network protocol handling and memory management, making it particularly dangerous as it can be triggered through normal network operations. The vulnerability demonstrates poor adherence to secure coding practices, specifically the lack of proper bounds checking and memory allocation validation that should be enforced during dynamic network parameter adjustments. Attackers can exploit this by crafting malicious network responses that trigger the reconnection sequence with manipulated MTU values, leading to controlled heap corruption.
The operational impact of CVE-2013-7098 extends beyond simple denial of service scenarios, as the heap overflow condition can potentially enable remote code execution on affected systems. Organizations utilizing OpenConnect VPN clients in their infrastructure face significant risk when operating with GnuTLS versions below 5.02, particularly in environments where network reconnections occur frequently or where MTU adjustments are common. The vulnerability affects enterprise networks, government agencies, and any organization relying on OpenConnect for secure remote access, as it can compromise the integrity of the entire VPN session. Systems that do not properly patch this vulnerability become potential entry points for attackers seeking to establish persistent access to corporate networks, making this issue particularly concerning from an attacker's perspective. The exploitability of this vulnerability is enhanced by the fact that it requires minimal user interaction, as the trigger occurs automatically during normal reconnection processes, making it a stealthy threat that can go undetected for extended periods.
Mitigation strategies for CVE-2013-7098 primarily focus on immediate software updates and configuration adjustments. Organizations should prioritize upgrading their OpenConnect client installations to versions that include GnuTLS 5.02 or later, which contain the necessary patches to address the heap overflow condition. System administrators should also implement network monitoring to detect unusual MTU adjustments that might indicate exploitation attempts. The ATT&CK framework categorizes this vulnerability under the technique of "Exploitation for Privilege Escalation" and "Command and Control" when exploited for persistent access. Additional defensive measures include implementing network segmentation to limit the impact of successful exploitation and establishing robust patch management processes that ensure timely updates of all VPN client software components. Security teams should also consider deploying intrusion detection systems capable of identifying anomalous reconnection patterns that could signal exploitation attempts, as well as conducting regular vulnerability assessments to identify other potential heap-based vulnerabilities within the network infrastructure.