CVE-2007-4311 in Linux
Summary
by MITRE
The xfer_secondary_pool function in drivers/char/random.c in the Linux kernel 2.4 before 2.4.35 performs reseed operations on only the first few bytes of a buffer, which might make it easier for attackers to predict the output of the random number generator, related to incorrect use of the sizeof operator.
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Analysis
by VulDB Data Team • 07/21/2021
The vulnerability described in CVE-2007-4311 represents a critical weakness in the Linux kernel's random number generation mechanism that affects versions prior to 2.4.35. This issue resides within the xfer_secondary_pool function located in drivers/char/random.c, which is responsible for managing the entropy pool that serves as the foundation for cryptographic security operations throughout the system. The flaw manifests when the function performs reseed operations on only a portion of a buffer rather than the entire buffer, creating a predictable pattern that compromises the randomness of the generated numbers.
The technical root cause of this vulnerability stems from an incorrect application of the sizeof operator within the kernel's random number generation code. Specifically, the function fails to properly calculate the buffer size when transferring entropy data from secondary pools to the primary entropy pool. This improper handling results in only the initial bytes of the buffer being processed during reseeding operations, leaving the remainder of the buffer unmodified and predictable. The incorrect use of sizeof operator directly violates the expected behavior of entropy management systems and creates a significant security gap that adversaries can exploit to compromise the randomness properties of the kernel's cryptographic primitives.
The operational impact of this vulnerability extends far beyond simple randomness prediction, as it fundamentally undermines the security of cryptographic operations that depend on the kernel's random number generator. Systems running affected kernel versions become vulnerable to attacks that can predict future random values, potentially compromising encryption keys, session identifiers, and other security-critical random data used by network protocols, authentication mechanisms, and cryptographic libraries. This weakness aligns with CWE-330, which addresses the use of insufficiently random values in security-sensitive contexts, and represents a clear violation of the principle that cryptographic random number generators must produce unpredictable outputs to maintain security guarantees.
The attack surface for this vulnerability is particularly concerning as it affects the core kernel functionality that underpins all security operations on Linux systems. Attackers who can predict the output of the random number generator can potentially forge cryptographic signatures, break encryption schemes, and impersonate legitimate users or systems. This vulnerability directly relates to ATT&CK technique T1083, which covers the discovery of system information, as attackers can leverage the predictable randomness to gather information about system state and security parameters. The impact is exacerbated by the fact that this vulnerability affects kernel-level operations, making it extremely difficult to detect and mitigate without a proper kernel update.
Mitigation of this vulnerability requires immediate deployment of kernel updates to version 2.4.35 or later, where the buffer processing logic has been corrected to properly handle the entire buffer during reseed operations. System administrators should prioritize patching affected systems, particularly those handling sensitive cryptographic operations or serving as security infrastructure components. Additionally, organizations should implement monitoring for unusual entropy consumption patterns and consider implementing additional entropy sources to compensate for the weakened randomness during the transition period. The fix addresses the core issue by ensuring that the sizeof operator correctly calculates buffer boundaries and that all bytes within the entropy buffer are properly processed during reseed operations, thereby restoring the cryptographic strength of the kernel's random number generation capabilities.