A certain pseudo-random number generator (PRNG) algorithm that uses ADD with 0 random hops (aka "Algorithm A0"), as used in OpenBSD 3.5 through 4.2 and NetBSD 1.6.2 through 4.0, allows remote attackers to guess sensitive values such as (1) DNS transaction IDs or (2) IP fragmentation IDs by observing a sequence of previously generated values. NOTE: this issue can be leveraged for attacks such as DNS cache poisoning, injection into TCP packets, and OS fingerprinting.
CVSS Severity (version 2.0):
Impact Subscore: 6.4
Exploitability Subscore: 8.6
CVSS Version 2 Metrics:
Access Vector: Network exploitable; Victim must voluntarily interact with attack mechanism
Access Complexity: Medium
Authentication: Not required to exploit
Impact Type: Allows unauthorized disclosure of information; Allows unauthorized modification; Allows disruption of service
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20080206 A paper by Amit Klein (Trusteer): "OpenBSD DNS Cache Poisoning and Multiple O/S Predictable IP ID Vulnerability"