CVE-2017-5972 in Linux
Summary
by MITRE
The TCP stack in the Linux kernel 3.x does not properly implement a SYN cookie protection mechanism for the case of a fast network connection, which allows remote attackers to cause a denial of service (CPU consumption) by sending many TCP SYN packets, as demonstrated by an attack against the kernel-3.10.0 package in CentOS Linux 7.
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Analysis
by VulDB Data Team • 12/20/2024
The vulnerability identified as CVE-2017-5972 represents a critical flaw in the Linux kernel's TCP stack implementation that specifically targets the SYN cookie protection mechanism. This weakness exists in kernel versions 3.x and manifests when handling TCP SYN packets over fast network connections, creating a scenario where remote attackers can exploit the system's resource management capabilities to achieve denial of service conditions. The vulnerability is particularly concerning because it directly impacts the fundamental network communication protocols that underpin virtually all internet services and applications.
The technical flaw resides in the kernel's handling of SYN cookies, which are designed to protect against SYN flood attacks by using cryptographic techniques to encode connection information in the SYN-ACK packets. When operating over fast network connections, the kernel fails to properly implement the SYN cookie mechanism, allowing attackers to send a large volume of TCP SYN packets that consume excessive CPU resources during connection establishment attempts. This occurs because the system cannot efficiently process the massive number of connection requests that would normally be handled through proper SYN cookie generation and validation. The vulnerability specifically affects the kernel-3.10.0 package running on CentOS Linux 7 systems, though it likely impacts other 3.x kernel versions as well.
The operational impact of this vulnerability extends beyond simple service disruption, creating conditions that can severely degrade system performance and availability. Attackers can consume CPU resources at an exponential rate by sending numerous SYN packets, effectively exhausting system processing capabilities and preventing legitimate connection attempts from being processed. This type of attack can be particularly devastating in production environments where network availability is critical, as it can render systems unresponsive to legitimate users while maintaining the appearance of normal operation. The resource consumption pattern aligns with attack techniques categorized under the MITRE ATT&CK framework's Network Denial of Service tactics, specifically targeting system resources through protocol manipulation.
The vulnerability's exploitation demonstrates a fundamental flaw in kernel network stack implementation that violates standard security practices for resource management and protocol handling. According to CWE classification, this represents a weakness in the implementation of a security mechanism where the system fails to properly validate or process network protocol elements, leading to resource exhaustion conditions. Organizations running affected kernel versions should implement immediate mitigations including kernel updates, network traffic filtering, and connection rate limiting measures. The recommended approach involves upgrading to kernel versions that properly implement SYN cookie protection for fast network connections, while also implementing network-level controls such as iptables rules to limit SYN packet rates and employing TCP SYN cookies as an additional protective layer. This vulnerability highlights the importance of thorough testing of security mechanisms under various network conditions and demonstrates how seemingly minor implementation details can create significant security risks in critical system components.