CVE-2021-45488 in NetBSD
Summary
by MITRE • 12/25/2021
In NetBSD through 9.2, there is an information leak in the TCP ISN (ISS) generation algorithm.
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Analysis
by VulDB Data Team • 12/27/2021
The vulnerability identified as CVE-2021-45488 represents a significant information disclosure issue within the NetBSD operating system's TCP implementation, specifically affecting versions through 9.2. This flaw resides in the TCP Initial Sequence Number generation algorithm which serves as a fundamental security mechanism in network communications. The TCP ISN generation algorithm is designed to produce unpredictable sequence numbers that prevent attackers from predicting future sequence numbers in TCP connections, thereby maintaining the integrity and security of network communications. When this algorithm fails to generate sufficiently random values, it creates opportunities for adversaries to exploit the predictability of sequence numbers.
The technical flaw in this vulnerability stems from weaknesses in the random number generation process used by NetBSD's TCP stack when creating Initial Sequence Numbers. The ISN generation algorithm in TCP is critical for security as it ensures that each connection begins with a unique and unpredictable sequence number that cannot be easily guessed by potential attackers. When the randomness is compromised, attackers can potentially predict future sequence numbers and execute various attacks including TCP sequence number prediction attacks, which can lead to connection hijacking and data manipulation. This vulnerability directly relates to CWE-330, which describes insufficient entropy in random number generation, and aligns with ATT&CK technique T1071.004 for application layer protocol traffic shaping and manipulation.
The operational impact of this vulnerability extends beyond simple information disclosure to encompass potential network compromise and data integrity violations. An attacker who successfully predicts TCP sequence numbers can potentially hijack active TCP connections, inject malicious data into established sessions, or perform man-in-the-middle attacks against network communications. This vulnerability is particularly concerning in environments where network security is paramount, such as enterprise networks, cloud environments, and systems handling sensitive data. The information leak aspect means that adversaries can gain insights into the system's TCP implementation characteristics, potentially aiding in the development of more sophisticated attacks against the affected system. This vulnerability also impacts the overall security posture of systems running NetBSD 9.2 or earlier, as it undermines the fundamental security assumptions that TCP connections should be resistant to prediction-based attacks.
Mitigation strategies for CVE-2021-45488 should prioritize immediate system updates to the latest NetBSD releases that contain fixes for the TCP ISN generation algorithm. System administrators should also consider implementing network-level protections such as TCP sequence number randomization techniques and monitoring for unusual network behavior that might indicate exploitation attempts. Additional defensive measures include network segmentation, intrusion detection systems, and regular security audits to identify potential exploitation of this vulnerability. The fix for this issue typically involves strengthening the random number generation algorithms used in the TCP stack to ensure that Initial Sequence Numbers are properly randomized and unpredictable. Organizations should also conduct thorough vulnerability assessments to determine if any systems are still running vulnerable versions of NetBSD and ensure proper patch management processes are in place to prevent similar issues in the future. This vulnerability highlights the critical importance of maintaining up-to-date security implementations and the need for continuous monitoring of system security mechanisms that form the foundation of network communications security.