CVE-2007-2453 in Linux
Summary
by MITRE
The random number feature in Linux kernel 2.6 before 2.6.20.13, and 2.6.21.x before 2.6.21.4, (1) does not properly seed pools when there is no entropy, or (2) uses an incorrect cast when extracting entropy, which might cause the random number generator to provide the same values after reboots on systems without an entropy source.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 07/20/2019
The vulnerability described in CVE-2007-2453 represents a critical weakness in the Linux kernel's cryptographic random number generation mechanism that affects versions prior to 2.6.20.13 and 2.6.21.4. This flaw resides in the kernel's handling of entropy pools and the initialization of random number generators, creating a predictable randomness issue that undermines the security of cryptographic operations relying on these values. The vulnerability specifically targets the /dev/random and /dev/urandom device interfaces that applications use to obtain cryptographically secure random numbers for key generation, session identifiers, and other security-sensitive operations.
The technical implementation of this vulnerability manifests in two distinct failure modes that compromise the entropy collection process. The first issue occurs when systems lack sufficient entropy sources, causing the kernel to fail to properly initialize or seed the entropy pools that are essential for generating unpredictable random numbers. This condition is particularly problematic on headless systems or virtualized environments where hardware entropy sources may be absent or insufficient. The second vulnerability involves incorrect casting operations during entropy extraction, which can lead to truncation or misinterpretation of entropy data, resulting in deterministic outputs that can be predicted by attackers. These flaws are categorized under CWE-330 Use of Insufficiently Random Values, which directly impacts the quality of randomness and cryptographic security.
The operational impact of this vulnerability extends far beyond simple predictability issues, as it fundamentally undermines the security of cryptographic protocols that depend on high-quality random numbers. Systems utilizing affected kernel versions may experience repeated cryptographic key generation, predictable session tokens, and compromised secure communications when the same random values are generated across reboots. This vulnerability aligns with ATT&CK technique T1083 (File and Directory Discovery) and T1583 (Acquire Access) as it enables attackers to potentially reconstruct cryptographic keys or session information, particularly in environments where entropy is limited or unavailable. The vulnerability is especially dangerous in server environments, embedded systems, and virtual machines where predictable random number generation can be exploited to break encryption, forge authentication tokens, or bypass security mechanisms that rely on unpredictable values.
Mitigation strategies for CVE-2007-2453 require immediate kernel upgrades to patched versions 2.6.20.13 or 2.6.21.4, respectively, which address both the entropy seeding issues and the casting errors in the random number generation code. Organizations should also implement entropy monitoring tools to detect insufficient entropy conditions and ensure that systems have adequate entropy sources such as hardware random number generators or entropy collection daemons. Additional protective measures include configuring applications to use alternative entropy sources, implementing entropy exhaustion detection, and ensuring that critical cryptographic operations are not performed on systems with known insufficient entropy conditions. The vulnerability demonstrates the critical importance of proper entropy management in cryptographic systems and highlights the need for robust random number generation in kernel-level security implementations.