CVE-2009-3238 in Linux
Summary
by MITRE
The get_random_int function in drivers/char/random.c in the Linux kernel before 2.6.30 produces insufficiently random numbers, which allows attackers to predict the return value, and possibly defeat protection mechanisms based on randomization, via vectors that leverage the function s tendency to "return the same value over and over again for long stretches of time."
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Analysis
by VulDB Data Team • 08/22/2021
The vulnerability described in CVE-2009-3238 represents a critical weakness in the Linux kernel's random number generation mechanism that fundamentally undermines cryptographic security. This flaw exists within the get_random_int function located in drivers/char/random.c, which serves as a core component for generating random numbers across the operating system. The vulnerability manifests as a significant degradation in entropy quality, where the random number generator fails to produce sufficiently unpredictable outputs. Attackers can exploit this weakness to predict future random values based on observed patterns, effectively compromising the randomness that security systems depend upon for protection mechanisms such as session tokens, cryptographic key generation, and other randomized security features. The specific behavior of returning the same value over extended periods creates a predictable pattern that can be analyzed and leveraged by malicious actors to defeat security protections that rely on proper randomization.
The technical implementation of this vulnerability stems from inadequate seeding and state management within the kernel's random number generator. The get_random_int function does not properly maintain sufficient entropy across successive calls, leading to prolonged sequences of identical or highly correlated outputs. This issue directly relates to CWE-330, which addresses insufficient entropy in random number generators, and specifically targets the fundamental principle that cryptographic random number generators must provide unpredictable outputs. The weakness allows for a form of temporal correlation where an attacker can observe multiple outputs from the function and use this information to reconstruct the internal state or predict future values. This vulnerability particularly affects systems where security relies on proper randomization, including those implementing cryptographic protocols, network security measures, and any system components that depend on unpredictable random values for their operation.
The operational impact of CVE-2009-3238 extends far beyond simple randomness issues, as it compromises the integrity of numerous security mechanisms that depend on unpredictable random values. Systems utilizing affected kernel versions become vulnerable to attacks that can predict session identifiers, cryptographic keys, and other security-critical random values. This weakness enables attackers to bypass security controls that rely on randomization, potentially allowing for session hijacking, key recovery attacks, and other exploits that would normally be prevented by proper randomization. The vulnerability's impact is particularly severe because it affects the underlying random number generation that supports multiple security features throughout the system, creating a cascading effect where various protection mechanisms become compromised. According to ATT&CK framework, this vulnerability maps to T1083 (File and Directory Discovery) and T1566 (Phishing with Social Engineering) as attackers can use predictable random values to craft more effective social engineering attacks or to bypass security controls that depend on randomization.
Mitigation strategies for CVE-2009-3238 require immediate kernel updates to versions 2.6.30 and later, where the random number generation has been significantly improved. Organizations should implement comprehensive patch management processes to ensure all systems are updated promptly, as this vulnerability affects the core kernel functionality. Additional defensive measures include monitoring for unusual patterns in system random number usage and implementing alternative random number sources for critical security applications. Security teams should also conduct thorough assessments of systems that rely heavily on kernel random number generation for cryptographic operations, ensuring that any applications depending on this functionality are properly updated or patched. The vulnerability highlights the importance of proper entropy management in cryptographic systems and demonstrates the critical need for robust random number generation in operating system kernels, as outlined in NIST SP 800-90A guidelines for random number generation.