CVE-2013-5173 in Mac OS X
Summary
by MITRE
The random-number generator in the kernel in Apple Mac OS X before 10.9 provides lengthy exclusive access for processing of large requests, which allows local users to cause a denial of service (temporary generator outage) via an application that requires many random numbers.
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Analysis
by VulDB Data Team • 05/31/2021
The vulnerability described in CVE-2013-5173 represents a significant weakness in the cryptographic random number generation implementation within Apple Mac OS X kernel versions prior to 10.9. This flaw stems from the kernel's handling of random number requests, specifically how it manages exclusive access to the random number generator during processing of large requests. The design allows for extended periods of exclusive access, creating a scenario where the random number generator becomes temporarily unavailable to other system processes. This issue falls under the category of weak random number generation as classified by CWE-330, which addresses the use of insufficiently random values in security-sensitive contexts. The vulnerability demonstrates a fundamental flaw in the kernel's resource management strategy for cryptographic operations.
The technical implementation of this vulnerability manifests when applications that require substantial quantities of random numbers make requests to the kernel's random number generator. During processing of these large requests, the generator maintains exclusive access for an extended duration, effectively blocking concurrent access from other legitimate system processes. This behavior creates a temporary outage condition where the random number generator cannot service additional requests, leading to a denial of service scenario. The issue is particularly concerning because random number generation is fundamental to cryptographic operations including key generation, session management, and security protocol implementation. The operational impact extends beyond simple service disruption, as it can compromise the security posture of the entire system by potentially weakening cryptographic implementations that depend on quality random numbers.
The exploitation of this vulnerability requires only local user access, making it particularly dangerous as it can be leveraged by malicious applications or compromised user accounts to disrupt system functionality. Attackers can craft applications that repeatedly request large volumes of random numbers, causing the generator to remain occupied and unavailable to other system components. This denial of service condition can affect critical system functions that rely on cryptographic random numbers, including secure network communications, file encryption, and authentication mechanisms. From an ATT&CK framework perspective, this vulnerability maps to privilege escalation and denial of service tactics, as it allows local users to disrupt system operations and potentially create conditions that could be exploited for further compromise. The vulnerability's impact is amplified by the fact that random number generation is a core system service that numerous applications depend upon.
Mitigation strategies for this vulnerability require immediate system updates to Mac OS X 10.9 or later versions where the kernel's random number generator implementation has been improved to handle concurrent access more efficiently. System administrators should also implement monitoring to detect unusual patterns of random number generation requests that might indicate exploitation attempts. The fix addresses the underlying design flaw by modifying how the kernel manages exclusive access to the random number generator, ensuring that large requests do not monopolize the resource for extended periods. Additional protective measures include implementing application whitelisting to prevent unauthorized applications from making excessive random number requests, and configuring system logging to track random number generation activity. Organizations should also consider implementing regular security assessments to identify other potential weaknesses in cryptographic implementations that could be similarly exploited. The vulnerability serves as a reminder of the critical importance of proper resource management in cryptographic system components and the potential for seemingly benign implementation details to create significant security risks.