CVE-2008-1147 in Darwin
Summary
by MITRE
A certain pseudo-random number generator (PRNG) algorithm that uses XOR and 2-bit random hops (aka "Algorithm X2"), as used in OpenBSD 2.6 through 3.4, Mac OS X 10 through 10.5.1, FreeBSD 4.4 through 7.0, and DragonFlyBSD 1.0 through 1.10.1, allows remote attackers to guess sensitive values such as IP fragmentation IDs by observing a sequence of previously generated values. NOTE: this issue can be leveraged for attacks such as injection into TCP packets and OS fingerprinting.
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Analysis
by VulDB Data Team • 09/19/2018
The vulnerability described in CVE-2008-1147 represents a critical weakness in the implementation of pseudo-random number generation across multiple operating systems including OpenBSD, Mac OS X, FreeBSD, and DragonFlyBSD. This flaw specifically affects the "Algorithm X2" PRNG which employs XOR operations combined with 2-bit random hops to generate sequences of numbers. The vulnerability stems from the predictability inherent in this particular algorithm design, where attackers can reconstruct the internal state of the generator by observing only a small sequence of previously generated values.
The technical implementation of Algorithm X2 creates a deterministic pattern that can be reverse-engineered through mathematical analysis of the observed output sequences. This weakness allows attackers to predict future values generated by the PRNG, which directly compromises the security of cryptographic operations and network protocols that depend on unpredictable number generation. The vulnerability is particularly dangerous because it affects core system components that generate critical values such as IP fragmentation IDs, which are essential for proper network packet handling and security mechanisms.
The operational impact of this vulnerability extends beyond simple predictability issues and enables sophisticated attacks including TCP injection and OS fingerprinting. Attackers can leverage the predictable nature of the PRNG to inject malicious packets into existing TCP connections by correctly guessing sequence numbers and other protocol-specific values. The ability to perform OS fingerprinting through predictable random number generation allows adversaries to determine the underlying operating system and version with high accuracy, facilitating targeted attacks against specific system configurations. This vulnerability directly violates the principle of entropy and randomness required for secure cryptographic operations as outlined in industry standards such as NIST SP 800-90A.
From a cybersecurity perspective, this vulnerability aligns with several ATT&CK tactics including reconnaissance and privilege escalation, as it enables attackers to gather intelligence about target systems and potentially gain unauthorized access through predictable network behavior. The weakness demonstrates poor implementation practices in cryptographic algorithm design, specifically violating CWE-330, which addresses insufficient entropy in random number generation. Organizations affected by this vulnerability face significant risk of network-level attacks that could compromise entire network infrastructures, as the predictability of fragmentation IDs and other system-generated values creates multiple attack vectors for man-in-the-middle and packet injection attacks.
Mitigation strategies should include immediate patching of affected operating systems to implement stronger PRNG algorithms, such as those based on cryptographically secure random number generators. System administrators should also implement network monitoring to detect anomalous packet patterns that might indicate exploitation attempts. Additionally, organizations should consider implementing network segmentation and additional security controls to limit the impact of potential exploitation. The vulnerability underscores the importance of proper cryptographic implementation and the necessity of using well-vetted, industry-standard random number generators that meet current security requirements as specified in various cryptographic standards and frameworks.