CVE-2012-4565 in Linux
Summary
by MITRE
The tcp_illinois_info function in net/ipv4/tcp_illinois.c in the Linux kernel before 3.4.19, when the net.ipv4.tcp_congestion_control illinois setting is enabled, allows local users to cause a denial of service (divide-by-zero error and OOPS) by reading TCP stats.
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Analysis
by VulDB Data Team • 04/19/2021
The vulnerability identified as CVE-2012-4565 represents a critical denial of service flaw within the Linux kernel's TCP congestion control implementation. This issue specifically affects systems running Linux kernel versions prior to 3.4.19 where the illinois congestion control algorithm is enabled through the net.ipv4.tcp_congestion_control configuration parameter. The flaw manifests in the tcp_illinois_info function located in the net/ipv4/tcp_illinois.c source file, which handles the retrieval and reporting of TCP statistics for the illinois algorithm.
The technical exploitation of this vulnerability occurs when local users attempt to read TCP statistics while the illinois congestion control mechanism is active. The underlying cause stems from a divide-by-zero error that occurs within the statistical calculation routines of the illinois algorithm implementation. When the tcp_illinois_info function processes requests for congestion control information, it performs mathematical operations that fail when encountering certain statistical conditions, resulting in a kernel panic or OOPS (Oops exception) condition. This type of error directly maps to CWE-369, which encompasses divide-by-zero vulnerabilities in software systems, and represents a classic kernel-level fault that can be exploited to disrupt system operations.
The operational impact of this vulnerability extends beyond simple service disruption, as it enables local attackers to effectively crash the kernel or render network services unavailable. The OOPS condition generated by the divide-by-zero error typically results in a kernel panic, forcing system administrators to reboot affected machines and potentially causing service interruptions that could affect critical network infrastructure. This vulnerability particularly impacts systems that rely heavily on TCP congestion control mechanisms, such as servers handling high volumes of network traffic or systems implementing specific network policies through the illinois algorithm.
The security implications of CVE-2012-4565 align with ATT&CK technique T1499.004, which covers network denial of service attacks through kernel-level exploitation. Organizations running affected kernel versions face significant risk as this vulnerability can be exploited by any local user with access to the system, making it particularly dangerous in multi-tenant environments or systems where privilege escalation is possible. The vulnerability demonstrates how seemingly minor statistical calculation errors in kernel code can result in catastrophic system failures, emphasizing the critical importance of thorough testing and validation of network stack implementations.
Mitigation strategies for this vulnerability primarily involve upgrading to Linux kernel version 3.4.19 or later, where the divide-by-zero condition has been properly addressed through defensive programming techniques. System administrators should also consider disabling the illinois congestion control algorithm if it is not actively required, using the command echo "tcp_congestion_control cubic" > /proc/sys/net/ipv4/tcp_congestion_control to switch to alternative algorithms such as cubic. Additionally, implementing proper access controls and monitoring for unauthorized attempts to read TCP statistics can help detect potential exploitation attempts, though the most effective defense remains the kernel upgrade to patched versions that resolve the underlying mathematical error in the statistical processing routines.