CVE-2015-20001 in Standard Library
Summary
by MITRE • 04/12/2021
In the standard library in Rust before 1.2.0, BinaryHeap is not panic-safe. The binary heap is left in an inconsistent state when the comparison of generic elements inside sift_up or sift_down_range panics. This bug leads to a drop of zeroed memory as an arbitrary type, which can result in a memory safety violation.
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Analysis
by VulDB Data Team • 04/15/2021
The vulnerability described in CVE-2015-20001 affects the Rust programming language's standard library implementation of BinaryHeap data structure prior to version 1.2.0. This represents a critical memory safety issue that stems from the lack of panic safety guarantees within the heap's internal operations. The BinaryHeap implementation in affected versions fails to maintain data structure integrity when comparison operations between generic elements encounter panics during heap maintenance procedures.
The technical flaw manifests in the sift_up and sift_down_range operations that are fundamental to maintaining the heap property during insertion and removal operations. When a comparison function provided by the user code panics during these operations, the heap structure becomes left in an inconsistent state. This inconsistency occurs because the heap operations do not properly handle the scenario where a panic interrupts the normal flow of heap maintenance, leaving internal data structures in a corrupted condition that violates Rust's memory safety guarantees.
The operational impact of this vulnerability is severe as it allows for the potential dropping of zeroed memory as an arbitrary type, which constitutes a memory safety violation. This behavior can lead to undefined behavior, memory corruption, and potentially exploitable conditions where malicious input could trigger the panic scenario and subsequently cause memory to be dropped as types that were never properly initialized. The vulnerability essentially allows for memory safety violations that could be leveraged to execute arbitrary code or cause system instability.
This vulnerability maps to CWE-665 Improper Initialization and CWE-476 NULL Pointer Dereference within the Common Weakness Enumeration framework, as it involves improper state management during heap operations and potential memory access violations. From an ATT&CK perspective, this corresponds to techniques involving memory corruption and privilege escalation through software vulnerabilities, particularly T1068 Valid Accounts and T1059 Command and Scripting Interpreter, as the vulnerability could be exploited to gain unauthorized access to system resources through memory corruption attacks.
The recommended mitigation strategy involves upgrading to Rust version 1.2.0 or later where the BinaryHeap implementation has been fixed to properly handle panic scenarios and maintain heap consistency even when comparison operations panic. Additionally, developers should avoid writing comparison functions that can panic, or ensure that such functions are properly wrapped to prevent panic propagation into heap maintenance operations. The fix implemented in Rust 1.2.0 ensures that heap operations are robust against panic conditions and maintain proper memory safety guarantees even in error scenarios.