CVE-2009-0638 in Firewall Services Module
Summary
by MITRE
The Cisco Firewall Services Module (FWSM) 2.x, 3.1 before 3.1(16), 3.2 before 3.2(13), and 4.0 before 4.0(6) for Cisco Catalyst 6500 switches and Cisco 7600 routers allows remote attackers to cause a denial of service (traffic-handling outage) via a series of malformed ICMP messages.
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Analysis
by VulDB Data Team • 11/29/2024
The Cisco Firewall Services Module FWSM vulnerability described in CVE-2009-0638 represents a critical denial of service weakness affecting multiple versions of Cisco's security infrastructure. This vulnerability specifically targets the FWSM 2.x, 3.1 before 3.1(16), 3.2 before 3.2(13), and 4.0 before 4.0(6) software versions deployed on Cisco Catalyst 6500 switches and Cisco 7600 routers. The flaw resides in the traffic-handling mechanisms of the FWSM, which processes incoming ICMP messages without proper validation of message structure and content. When malicious actors send a series of malformed ICMP packets to the affected devices, the system fails to properly handle these invalid packets, leading to complete traffic-handling outages that can disrupt network connectivity and security services.
The technical implementation of this vulnerability stems from inadequate input validation within the ICMP processing subsystem of the FWSM software. According to CWE-20 standards for Improper Input Validation, the system fails to properly validate the structure and content of incoming ICMP messages before processing them. The attack vector requires remote access to the network infrastructure, allowing malicious actors to send crafted ICMP packets that exploit buffer handling and packet parsing flaws in the FWSM's network processing engine. This particular vulnerability does not require authentication or special privileges to exploit, making it particularly dangerous as it can be leveraged by any remote attacker with network access to the affected devices.
The operational impact of this vulnerability extends beyond simple service disruption to encompass complete network security infrastructure failure. When exploited successfully, the malformed ICMP messages cause the FWSM to enter an unstable state where it cannot properly process legitimate network traffic, effectively creating a denial of service condition that affects all security services provided by the module. This includes firewall rules enforcement, intrusion prevention capabilities, and network access control functions that depend on the FWSM's proper operation. The vulnerability's potential for widespread impact is significant given that these devices are commonly deployed in enterprise and service provider networks as core security appliances, where their failure can cascade across multiple network segments and affect critical business operations.
Security practitioners should implement immediate mitigation strategies including applying the relevant Cisco security patches and updates released to address this vulnerability. Network administrators should consider implementing ICMP filtering rules at network boundaries to limit the exposure of affected devices to potentially malicious ICMP traffic. The vulnerability aligns with ATT&CK technique T1498 for Network Denial of Service, which describes methods of disrupting network services through various attack vectors. Organizations should also implement network monitoring solutions to detect unusual ICMP traffic patterns that could indicate exploitation attempts. Additionally, the vulnerability demonstrates the importance of proper input validation and robust error handling in network security appliances, as outlined in security best practices for network infrastructure devices. Regular security assessments and vulnerability management processes should be enhanced to identify and remediate similar flaws in network security equipment across the enterprise infrastructure.