CVE-2011-3188 in Linux
Summary
by MITRE
The (1) IPv4 and (2) IPv6 implementations in the Linux kernel before 3.1 use a modified MD4 algorithm to generate sequence numbers and Fragment Identification values, which makes it easier for remote attackers to cause a denial of service (disrupted networking) or hijack network sessions by predicting these values and sending crafted packets.
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Analysis
by VulDB Data Team • 12/02/2021
The vulnerability described in CVE-2011-3188 represents a critical weakness in the Linux kernel's network stack implementation that affects both IPv4 and IPv6 protocols. This flaw stems from the use of a modified MD4 algorithm for generating sequence numbers and fragment identification values, which fundamentally undermines the security and reliability of network communications. The vulnerability exists in Linux kernel versions prior to 3.1, making it a widespread issue affecting numerous systems and deployments. The implementation of such a weak cryptographic primitive in core network functionality creates a significant attack surface that adversaries can exploit to disrupt normal network operations.
The technical flaw lies in the cryptographic weakness of the modified MD4 algorithm used for generating network sequence numbers and fragment identification values. Sequence numbers in TCP connections and fragment identification values in IP packets are critical for maintaining connection integrity and proper packet reassembly. When these values are generated using a predictable algorithm instead of a proper cryptographically secure random number generator, attackers can potentially predict future values. This prediction capability allows malicious actors to inject packets into existing connections or cause packet reordering that leads to connection disruption. The vulnerability specifically impacts the network stack's ability to maintain secure and reliable communication channels, as the predictability of these values compromises the fundamental security assumptions of transport layer protocols.
The operational impact of this vulnerability extends beyond simple denial of service conditions to include active session hijacking capabilities. Remote attackers can leverage the predictable sequence numbers and fragment identifiers to inject malicious packets into established connections, potentially taking control of network sessions. This capability enables man-in-the-middle attacks where attackers can manipulate traffic without being detected, leading to data compromise and service disruption. The vulnerability affects both IPv4 and IPv6 implementations, meaning that systems running either protocol are equally at risk, making it particularly dangerous in mixed network environments. The disruption of networking operations can result in complete service outages, data loss, and unauthorized access to network resources, with potential cascading effects throughout interconnected systems.
The vulnerability maps to CWE-327, which specifically addresses the use of weak cryptographic algorithms, and aligns with ATT&CK technique T1071.004 for application layer protocol manipulation. Organizations should immediately upgrade to Linux kernel version 3.1 or later to remediate this vulnerability. Additionally, implementing network segmentation, monitoring for unusual packet patterns, and deploying intrusion detection systems can help detect exploitation attempts. The fix involves replacing the modified MD4 algorithm with proper cryptographically secure random number generation mechanisms. Regular security assessments and kernel updates should be part of standard operational procedures to prevent similar vulnerabilities from being introduced into network infrastructure. This vulnerability highlights the critical importance of using well-vetted cryptographic implementations in security-critical system components and demonstrates how seemingly minor implementation details can have major security implications.