CVE-2009-0628 in IOS
Summary
by MITRE
Memory leak in the SSLVPN feature in Cisco IOS 12.3 through 12.4 allows remote attackers to cause a denial of service (memory consumption and device crash) by disconnecting an SSL session in an abnormal manner, leading to a Transmission Control Block (TCB) leak.
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Analysis
by VulDB Data Team • 08/31/2019
The vulnerability identified as CVE-2009-0628 represents a critical memory management flaw within Cisco IOS software versions 12.3 through 12.4, specifically affecting the Secure Socket Layer Virtual Private Network implementation. This issue manifests as a memory leak condition that occurs when SSL VPN sessions are terminated abruptly or in an abnormal manner, creating a persistent degradation of system resources. The vulnerability resides in the handling of Transmission Control Block structures, which are fundamental data structures used to manage TCP connections within the network stack. When an SSL session is disconnected improperly, the system fails to properly release the associated TCB memory resources, leading to progressive memory exhaustion over time.
The technical exploitation of this vulnerability requires remote attackers to establish an SSL VPN session and then deliberately terminate it in a manner that bypasses normal session cleanup procedures. This abnormal disconnection pattern causes the system to maintain references to memory blocks that should have been freed, resulting in a gradual accumulation of unreleased memory segments. The flaw specifically impacts the TCP connection management subsystem within the IOS kernel, where TCB structures are allocated to track connection state information including sequence numbers, window sizes, and other critical TCP parameters. As these structures accumulate without proper cleanup, they consume valuable system memory that could otherwise be utilized for legitimate network operations.
The operational impact of this vulnerability extends beyond simple resource exhaustion to potentially cause complete system instability and service disruption. When memory consumption reaches critical levels, the affected Cisco IOS device may experience significant performance degradation, application timeouts, or complete system crashes. Network administrators may observe symptoms including increased CPU utilization, reduced available memory, and intermittent connectivity issues that can affect multiple network services. The vulnerability is particularly dangerous in enterprise environments where SSL VPN services are heavily utilized, as sustained exploitation can lead to extended outages and service interruptions that impact business continuity. This type of denial of service condition directly violates the availability principles of the CIA security triad and can result in substantial operational disruption.
Mitigation strategies for CVE-2009-0628 should focus on both immediate remediation and long-term architectural improvements to prevent similar memory management issues. Cisco recommends applying the appropriate software patches and updates that address the specific memory leak in the SSL VPN implementation, which typically involve modifications to the TCP connection cleanup routines and improved memory deallocation procedures. Network administrators should implement monitoring solutions to detect unusual memory consumption patterns and establish automated alerting mechanisms when memory usage exceeds predefined thresholds. Additionally, implementing connection rate limiting and session timeout configurations can help reduce the likelihood of exploitation by limiting the number of concurrent sessions that can be established. The vulnerability aligns with CWE-401, which describes improper cleanup of memory resources, and represents a classic example of how improper resource management can lead to denial of service conditions. From an ATT&CK framework perspective, this vulnerability could be leveraged during the Execution and Resource Exhaustion phases of an attack, where adversaries seek to consume system resources to disrupt legitimate operations. Organizations should also consider implementing network segmentation strategies to isolate SSL VPN services and limit the potential impact of such vulnerabilities on critical network infrastructure.