CVE-2020-35889 in crayon Crate
Summary
by MITRE • 12/31/2020
An issue was discovered in the crayon crate through 2020-08-31 for Rust. A TOCTOU issue has a resultant memory safety violation via HandleLike.
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Analysis
by VulDB Data Team • 12/31/2020
The vulnerability identified in the crayon crate version through 2020-08-31 represents a classic time-of-check to time-of-use race condition that manifests as a memory safety violation through the HandleLike trait implementation. This type of vulnerability occurs when an application checks the state of a resource and then uses that resource without revalidating the check, creating a window where another thread or process can modify the resource between the check and usage phases. The specific manifestation in this crate involves the HandleLike trait which likely provides methods for managing handles to system resources such as file descriptors, memory regions, or other kernel objects.
The technical flaw stems from improper synchronization mechanisms within the crayon crate's implementation of handle management operations. When a caller performs a check operation on a resource and subsequently accesses that same resource without proper locking or validation, the system may encounter undefined behavior if the resource state has changed during the intervening period. This particular vulnerability leverages the HandleLike trait to access memory regions that are not properly protected against concurrent access patterns, leading to potential memory corruption, information disclosure, or denial of service conditions. The timing window between the check and use operations creates opportunities for malicious actors to manipulate the underlying resource state.
The operational impact of this vulnerability extends beyond simple memory safety issues as it can be exploited to bypass security controls that rely on proper resource validation. Attackers could potentially leverage this race condition to escalate privileges, access restricted resources, or cause system instability through controlled manipulation of handle states during the check-use window. The vulnerability affects any application that utilizes the crayon crate's HandleLike implementations and depends on the specific timing patterns where concurrent access can occur between validation and actual resource usage operations. This makes it particularly dangerous in multi-threaded environments or systems where multiple processes might interact with the same resource handles.
Mitigation strategies for this vulnerability should focus on implementing proper synchronization mechanisms such as mutexes, atomic operations, or other concurrency control primitives to ensure that resource checks and uses occur atomically. The recommended approach involves modifying the HandleLike trait implementations to include appropriate locking mechanisms that prevent concurrent access during critical sections where resource state validation occurs. Additionally, developers should consider using memory safety patterns that avoid the race condition entirely by eliminating the need for separate check and use operations through atomic operations or by redesigning the API to provide guaranteed safe access patterns. This vulnerability aligns with CWE-362 which describes "Concurrent Execution using Shared Resource with Improper Synchronization" and could potentially map to ATT&CK technique T1059 for privilege escalation through memory corruption exploits. The fix requires careful code review of all HandleLike implementations and thorough testing under concurrent access scenarios to ensure that the race condition window has been eliminated.