CVE-2003-0259 in VPN 30xx Concentrator
Summary
by MITRE
Cisco VPN 3000 series concentrators and Cisco VPN 3002 Hardware Client 2.x.x through 3.6.7 allows remote attackers to cause a denial of service (reload) via a malformed SSH initialization packet.
Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.
Analysis
by VulDB Data Team • 01/21/2025
The vulnerability identified as CVE-2003-0259 affects Cisco VPN 3000 series concentrators and Cisco VPN 3002 Hardware Client versions 2.x.x through 3.6.7, representing a critical denial of service weakness that can be exploited remotely. This flaw specifically targets the Secure Shell protocol implementation within these networking devices, creating a pathway for attackers to disrupt network connectivity and force system reloads. The vulnerability stems from inadequate input validation during the SSH initialization process, where malformed packets can trigger unexpected behavior in the device's processing logic.
The technical exploitation of this vulnerability occurs when an attacker crafts and transmits a specially formatted SSH initialization packet that violates the expected protocol structure. This malformed packet triggers a buffer overflow or parsing error within the SSH service implementation of the affected Cisco devices, leading to system instability and ultimately forcing the device to reboot automatically. The flaw exists at the protocol level where the system fails to properly validate incoming SSH handshake messages before processing them, creating a condition where malformed data can cause the application to crash or enter an undefined state. This type of vulnerability is classified as a CWE-121 heap-based buffer overflow or CWE-122 stack-based buffer overflow depending on the specific implementation details.
The operational impact of this vulnerability extends beyond simple service disruption, as it can severely compromise network availability and business continuity for organizations relying on these Cisco VPN concentrators. When exploited, the denial of service attack forces the device to reload its operating system, resulting in temporary loss of VPN connectivity for all users connected through that concentrator. Network administrators may experience significant downtime while the device restarts and re-establishes connections, potentially affecting remote workers and branch office connectivity. The vulnerability affects organizations using Cisco's legacy VPN solutions, which were widely deployed in enterprise environments during the early 2000s, making it particularly concerning for legacy network infrastructure that may not have been properly updated or patched.
Mitigation strategies for this vulnerability should include immediate implementation of Cisco's security patches and updates that address the SSH initialization packet validation issues. Network administrators should also implement network segmentation and access control measures to limit exposure, including restricting SSH access to only trusted management networks and implementing intrusion detection systems to monitor for suspicious SSH traffic patterns. The vulnerability aligns with ATT&CK technique T1499.004 for network denial of service and represents a classic example of how protocol-level flaws can be exploited to compromise system availability. Organizations should also consider implementing redundant VPN concentrators and failover mechanisms to minimize the impact of such attacks on overall network operations. Regular security assessments and vulnerability scanning should be conducted to identify similar weaknesses in other network components, as this vulnerability demonstrates the importance of proper input validation in network protocol implementations.