CVE-2002-2111 in Fwmon
Summary
by MITRE
Fwmon before 1.0.10 allows remote attackers to cause a denial of service (crash) by causing the kernel to return a large packet.
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Analysis
by VulDB Data Team • 06/11/2018
The vulnerability identified as CVE-2002-2111 affects fwmon versions prior to 1.0.10, representing a critical denial of service flaw that can be exploited remotely by attackers. This issue specifically targets the kernel packet handling mechanisms within the fwmon system, which is designed for firewall monitoring and packet inspection. The vulnerability arises from insufficient input validation and improper handling of packet data structures when the kernel processes unusually large network packets. Attackers can exploit this weakness by crafting and transmitting specially formatted packets that exceed normal size parameters, causing the fwmon application to crash or become unresponsive. The flaw demonstrates a classic buffer overflow or memory management issue where the system fails to properly validate packet sizes before processing them, leading to unpredictable behavior and system instability.
The technical implementation of this vulnerability stems from the fwmon application's failure to implement proper packet size limits and validation checks within its kernel interface. When the kernel receives a packet larger than expected, the fwmon monitoring process attempts to handle this oversized data structure without adequate safeguards, resulting in memory corruption or resource exhaustion. This type of vulnerability aligns with CWE-122, which describes buffer overflow conditions where insufficient bounds checking allows attackers to write beyond allocated memory regions. The flaw exists at the intersection of kernel-level packet processing and user-space monitoring, creating a pathway for malicious packet construction to directly impact system stability. The vulnerability's remote exploitability means that attackers do not require local access or credentials, making it particularly dangerous in networked environments where fwmon is actively monitoring traffic.
The operational impact of CVE-2002-2111 extends beyond simple system crashes, as it can result in complete service disruption for firewall monitoring capabilities. Organizations relying on fwmon for network security monitoring would experience immediate loss of visibility into their network traffic, potentially leaving critical security gaps during the system recovery period. The denial of service can be sustained through repeated attacks, effectively disabling the monitoring system for extended periods until manual intervention or system restart occurs. This vulnerability directly impacts the availability aspect of the CIA triad, compromising the system's ability to maintain continuous operation. The flaw also creates opportunities for more sophisticated attacks, as the system instability may provide cover for other exploitation attempts or allow attackers to establish persistence through system recovery processes. Network administrators may find their security monitoring tools rendered ineffective, potentially masking other malicious activities occurring within the network.
Mitigation strategies for CVE-2002-2111 primarily focus on immediate patching and implementation of network-level protections. Organizations should upgrade to fwmon version 1.0.10 or later, which includes proper packet size validation and memory management improvements. Network administrators should implement rate limiting and packet filtering rules at network boundaries to prevent oversized packets from reaching the affected systems. The solution aligns with ATT&CK technique T1499.001, which covers network denial of service attacks, by implementing defensive measures that limit the impact of such attacks. Additional protective measures include configuring firewall rules to drop packets exceeding predetermined size thresholds, implementing intrusion detection systems to monitor for suspicious packet patterns, and establishing robust monitoring procedures to detect service disruptions. System administrators should also consider implementing redundant monitoring solutions and regular system health checks to quickly identify and respond to similar vulnerabilities. The fix demonstrates proper input validation and bounds checking practices that prevent memory corruption issues, establishing a baseline for secure packet handling in network monitoring applications.