CVE-2021-45487 in NetBSD
Summary
by MITRE • 12/25/2021
In NetBSD through 9.2, the IPv4 ID generation algorithm does not use appropriate cryptographic measures.
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Analysis
by VulDB Data Team • 12/27/2021
The vulnerability identified as CVE-2021-45487 affects NetBSD operating systems through version 9.2 and centers on the IPv4 identification field generation algorithm within the network stack. This flaw represents a significant security concern as it undermines the fundamental integrity of IP packet transmission and can be exploited to compromise network communications. The IPv4 identification field serves as a crucial component in packet fragmentation and reassembly processes, where each packet must contain a unique identifier to ensure proper reconstruction at the destination. When this identifier lacks sufficient randomness or cryptographic strength, it creates predictable patterns that adversaries can exploit to perform various malicious activities.
The technical flaw stems from the implementation of the IPv4 ID generation algorithm which fails to incorporate appropriate cryptographic measures to ensure sufficient entropy and unpredictability. This weakness allows attackers to predict future identification values that will be used in IP packets, potentially enabling them to perform spoofing attacks, packet injection, or manipulation of fragmented packets. The algorithm's lack of cryptographic strength directly violates security principles established in industry standards such as the Common Weakness Enumeration which categorizes this as a weakness related to improper randomness generation. The vulnerability specifically impacts the network layer functionality where IP packet identification values are generated, creating a window of opportunity for attackers to exploit predictable patterns in network traffic.
The operational impact of CVE-2021-45487 extends beyond simple packet manipulation to encompass broader network security implications. Attackers leveraging this vulnerability can potentially perform session hijacking, bypass network security controls, or conduct more sophisticated attacks such as TCP sequence number prediction that can lead to complete network compromise. The vulnerability affects any system running NetBSD 9.2 or earlier versions where IPv4 traffic is processed, making it particularly concerning for network infrastructure components, servers, and devices that rely on predictable IP packet handling. This weakness can be exploited across various attack vectors including man-in-the-middle scenarios, network reconnaissance, and traffic analysis attacks that depend on understanding or predicting packet identification values.
Mitigation strategies for CVE-2021-45487 primarily involve upgrading to NetBSD versions that address this vulnerability through improved cryptographic measures in the IPv4 ID generation algorithm. System administrators should prioritize patching affected systems and implementing network monitoring to detect potential exploitation attempts. The solution aligns with ATT&CK framework techniques related to privilege escalation and defense evasion by ensuring that network protocols maintain their integrity and unpredictability. Additional defensive measures include implementing network segmentation, deploying intrusion detection systems that monitor for anomalous packet identification patterns, and ensuring that network devices properly handle packet fragmentation without exposing predictable identifiers. Organizations should also consider implementing cryptographic random number generation libraries and following security best practices for entropy collection to prevent similar weaknesses in other network protocol implementations.