CVE-2016-2070 in Linux
Summary
by MITRE • 01/25/2023
The tcp_cwnd_reduction function in net/ipv4/tcp_input.c in the Linux kernel before 4.3.5 allows remote attackers to cause a denial of service (divide-by-zero error and system crash) via crafted TCP traffic.
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Analysis
by VulDB Data Team • 01/25/2023
The vulnerability identified as CVE-2016-2070 represents a critical flaw in the Linux kernel's Transmission Control Protocol implementation that affects systems running kernel versions prior to 4.3.5. This issue resides within the tcp_cwnd_reduction function located in the net/ipv4/tcp_input.c source file, which governs how the kernel handles congestion control mechanisms in TCP connections. The flaw manifests when the kernel processes specially crafted TCP packets that trigger a divide-by-zero error during the congestion window reduction calculation, ultimately leading to system crashes and denial of service conditions. The vulnerability is particularly concerning because it can be exploited remotely through network-based attacks without requiring any local privileges or authentication.
The technical root cause of this vulnerability stems from inadequate input validation within the tcp_cwnd_reduction function where the kernel fails to properly handle cases where the congestion window value becomes zero or invalid during the reduction process. When malicious TCP packets are transmitted with specific sequence numbers and window sizing parameters, they can force the kernel's TCP stack to attempt a division operation by zero, which in turn triggers a kernel panic and system crash. This type of error falls under the CWE-369 vulnerability classification, specifically CWE-369: Divide by Zero, which is categorized as a weakness in the input validation and error handling mechanisms of software systems. The flaw demonstrates a classic example of how improper boundary condition handling in kernel space can lead to catastrophic system failures.
From an operational perspective, this vulnerability presents significant risks to network infrastructure and server availability since any system processing TCP traffic could potentially be affected. Attackers can exploit this weakness by sending carefully constructed TCP packets to target systems, causing immediate denial of service conditions that may require system rebooting to recover from. The impact extends beyond simple service disruption as the vulnerability can affect critical network services, web servers, database systems, and any infrastructure relying on TCP connectivity. Network administrators and security teams face the challenge of identifying and mitigating this issue across their entire network infrastructure, particularly in environments where untrusted network traffic flows through critical systems. The vulnerability also aligns with ATT&CK technique T1499.004, which covers Network Denial of Service attacks, demonstrating how this flaw can be leveraged to disrupt network availability and service continuity.
Mitigation strategies for CVE-2016-2070 primarily focus on kernel version upgrades to 4.3.5 or later, which contain the necessary patches to prevent the divide-by-zero condition in the tcp_cwnd_reduction function. System administrators should prioritize patching all affected systems and implementing network monitoring to detect potentially malicious TCP traffic patterns that could indicate exploitation attempts. Additional defensive measures include implementing TCP stack hardening configurations, deploying intrusion detection systems to monitor for suspicious traffic patterns, and establishing network segmentation to limit the potential impact of successful attacks. Organizations should also consider implementing rate limiting and connection tracking mechanisms to reduce the effectiveness of potential exploitation attempts while maintaining legitimate network operations. The vulnerability underscores the importance of maintaining up-to-date kernel versions and proper security patch management processes to protect against known exploits that could compromise system availability and stability.