CVE-2002-1095 in VPN 3002 Hardware Client
Summary
by MITRE
Cisco VPN 3000 Concentrator before 2.5.2(F), with encryption enabled, allows remote attackers to cause a denial of service (reload) via a Windows-based PPTP client with the "No Encryption" option set.
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Analysis
by VulDB Data Team • 05/16/2019
The vulnerability identified as CVE-2002-1095 affects Cisco VPN 3000 Concentrator devices running firmware versions prior to 2.5.2(F) when encryption is enabled. This issue represents a significant security weakness that can be exploited to disrupt network connectivity and force system reloads. The vulnerability specifically targets the processing of Point-to-Point Tunneling Protocol connections from Windows-based clients that have been configured with the "No Encryption" option. The attack vector leverages the interaction between the client configuration and the concentrator's encryption handling mechanisms, creating a condition that leads to system instability and forced restarts.
The technical flaw stems from inadequate input validation and state handling within the VPN concentrator's PPTP processing module. When a Windows PPTP client with the "No Encryption" setting connects to the Cisco VPN 3000 Concentrator, the system fails to properly validate the client's encryption parameters against the configured encryption settings. This mismatch creates a buffer overflow or memory corruption condition that ultimately results in the device performing an automatic system reload. The vulnerability exists because the concentrator does not adequately sanitize or validate the encryption negotiation parameters received from PPTP clients, particularly when those clients are configured to disable encryption while the server requires encryption.
From an operational impact perspective, this vulnerability poses a serious threat to network availability and business continuity. The denial of service condition can be triggered remotely without requiring authentication, making it particularly dangerous for organizations that rely on continuous VPN connectivity for remote access. Network administrators may experience unexpected service interruptions, potentially disrupting critical business operations, employee productivity, and customer access to services. The automatic reload process can also result in temporary loss of network connectivity for legitimate users and may cause the loss of active connections, requiring manual intervention to restore service. This vulnerability directly impacts the availability aspect of the CIA triad and can be classified under CWE-121 for buffer overflow conditions.
The exploitability of this vulnerability aligns with ATT&CK technique T1499.004 for network denial of service attacks, where adversaries leverage system weaknesses to disrupt availability. Security professionals should note that this vulnerability demonstrates the importance of proper protocol validation and input sanitization in network infrastructure devices. The issue highlights the need for comprehensive testing of edge devices against various client configurations and the importance of maintaining up-to-date firmware versions to protect against known vulnerabilities. Organizations should implement monitoring for unusual system reload patterns and consider network segmentation to limit the impact of such attacks. The vulnerability also underscores the importance of following security best practices such as disabling unnecessary services and implementing proper access controls to minimize the attack surface.
Mitigation strategies should focus on immediate firmware upgrades to version 2.5.2(F) or later, which contain patches addressing the specific validation issues in the PPTP processing module. Network administrators should also implement monitoring solutions that can detect unusual reload patterns or unauthorized connection attempts to the VPN concentrator. Additionally, organizations should review and enforce proper client configuration policies to prevent the use of incompatible encryption settings. The vulnerability serves as a reminder of the critical importance of maintaining current security patches and conducting regular vulnerability assessments of network infrastructure components. Organizations should also consider implementing intrusion detection systems that can identify and alert on suspicious PPTP connection patterns that may indicate exploitation attempts.