CVE-2021-45484 in NetBSD
Summary
by MITRE • 12/25/2021
In NetBSD through 9.2, the IPv6 fragment ID generation algorithm employs a weak cryptographic PRNG.
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Analysis
by VulDB Data Team • 12/27/2021
The vulnerability identified as CVE-2021-45484 affects NetBSD operating systems through version 9.2 and centers on a critical weakness in the IPv6 fragment identification generation process. This flaw resides in the network stack's handling of IPv6 packet fragmentation where the system relies on a weak pseudo-random number generator for creating fragment identifiers. The issue stems from the use of a non-cryptographically secure random number generation algorithm that fails to provide adequate entropy for generating unique fragment IDs, thereby creating predictable patterns that can be exploited by malicious actors.
The technical implementation of this vulnerability involves the IPv6 fragment ID generation algorithm which is responsible for assigning unique identifiers to fragments of IPv6 packets that exceed the maximum transmission unit. When network packets are fragmented, each fragment must carry a unique identification value to ensure proper reassembly at the destination. The weakness lies in how NetBSD generates these identifiers using a PRNG that lacks cryptographic security properties, making it susceptible to prediction and manipulation. This vulnerability directly maps to CWE-330, which specifically addresses the use of insufficiently random values in cryptographic contexts, and can be categorized under the broader category of weak randomness in network protocols.
The operational impact of this vulnerability extends beyond simple network disruption to encompass potential security breaches and man-in-the-middle attack opportunities. An attacker who can predict fragment IDs can potentially inject malicious packets into ongoing IPv6 connections, manipulate packet flow, or perform fragmentation-based attacks that exploit the predictability of the identifier generation. This weakness particularly affects network security in environments where IPv6 is actively used, potentially allowing attackers to bypass certain network security controls that rely on the uniqueness of fragment identifiers for proper operation. The vulnerability can be leveraged in conjunction with other network-based attacks to create more sophisticated exploitation scenarios.
Mitigation strategies for CVE-2021-45484 require immediate system updates to patched versions of NetBSD where the PRNG implementation has been strengthened to use cryptographically secure random number generation. System administrators should prioritize updating affected NetBSD installations to versions that address this specific weakness in the IPv6 fragment ID generation algorithm. Additionally, network monitoring should be enhanced to detect unusual fragmentation patterns that might indicate exploitation attempts. The mitigation approach aligns with ATT&CK technique T1071.004 which covers application layer protocol: DNS, and emphasizes the importance of secure random number generation in network protocol implementations. Organizations should also consider implementing network segmentation and access controls to limit the potential impact of successful exploitation attempts, while maintaining continuous monitoring for any signs of fragment-based attack patterns that could indicate the presence of this vulnerability in their network infrastructure.