CVE-2017-1082 in FreeBSD
Summary
by MITRE
In FreeBSD 11.x before 11.1-RELEASE and 10.x before 10.4-RELEASE, the qsort algorithm has a deterministic recursion pattern. Feeding a pathological input to the algorithm can lead to excessive stack usage and potential overflow. Applications that use qsort to handle large data set may crash if the input follows the pathological pattern.
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Analysis
by VulDB Data Team • 03/23/2020
The vulnerability described in CVE-2017-1082 represents a critical weakness in the FreeBSD operating system's implementation of the qsort algorithm that affects versions prior to specific release points. This issue stems from the deterministic nature of the sorting algorithm's recursive behavior, creating predictable patterns that can be exploited by malicious actors. The qsort function, which is a fundamental component of many applications and system utilities, becomes vulnerable when processing specific input patterns that cause excessive recursion depth. The problem manifests in scenarios where applications rely heavily on qsort for handling large datasets, making it particularly concerning for systems that process substantial amounts of data regularly. The deterministic recursion pattern means that attackers can potentially craft inputs that will cause the algorithm to follow a specific recursive path that consumes disproportionate amounts of stack memory.
The technical flaw resides in the implementation of the quicksort algorithm within the FreeBSD libc library, where the recursion depth becomes predictable and potentially exploitable. When the qsort function encounters data that follows a specific pathological pattern, it tends to make recursive calls that result in stack exhaustion rather than efficient sorting. This behavior violates the expected performance characteristics of a sorting algorithm and creates a potential denial of service condition. The vulnerability specifically affects systems running FreeBSD 11.x versions before 11.1-RELEASE and 10.x versions before 10.4-RELEASE, indicating that the issue was present in the standard library implementations across these major versions. The deterministic nature of the recursion means that the same input pattern will consistently produce the same recursive behavior, making this vulnerability both predictable and exploitable.
The operational impact of this vulnerability extends beyond simple denial of service scenarios, potentially affecting the stability and reliability of systems that depend on qsort for data processing. Applications that handle large datasets, including database systems, network processing utilities, and file management tools, could experience crashes or system instability when processing maliciously crafted input. The vulnerability particularly affects systems where qsort is used extensively in data handling workflows, as even a single malicious input could cause complete application failure. In server environments, this could lead to service disruption for multiple users or applications that rely on the affected sorting functionality. The potential for stack overflow also raises concerns about memory corruption and arbitrary code execution in scenarios where the overflow could be leveraged as part of a broader attack vector.
Mitigation strategies for CVE-2017-1082 focus primarily on upgrading to patched versions of FreeBSD where the qsort implementation has been corrected to prevent deterministic recursion patterns. System administrators should prioritize updating their FreeBSD installations to versions 11.1-RELEASE or later and 10.4-RELEASE or later, as these releases contain fixes that address the predictable recursion issue. Additionally, organizations should implement input validation and sanitization measures to prevent potentially malicious data from reaching applications that use qsort. The fix typically involves modifying the qsort algorithm implementation to use iterative approaches or randomized pivot selection to eliminate the deterministic recursion patterns that make exploitation possible. Security monitoring should also include detection of unusual qsort usage patterns that might indicate attempts to exploit this vulnerability, aligning with best practices from the CWE standard for sorting algorithm weaknesses and the ATT&CK framework's approach to privilege escalation through system utilities. Organizations should also consider implementing stack overflow protection mechanisms and monitoring for abnormal memory usage patterns in applications that rely heavily on sorting functions.