CVE-2020-36208 in conquer-once Crate
Summary
by MITRE • 01/26/2021
An issue was discovered in the conquer-once crate before 0.3.2 for Rust. Thread crossing can occur for a non-Send but Sync type, leading to memory corruption.
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Analysis
by VulDB Data Team • 02/20/2021
The vulnerability identified as CVE-2020-36208 affects the conquer-once crate version 0.3.1 and earlier in the Rust programming ecosystem. This issue represents a critical concurrency flaw that undermines the memory safety guarantees typically provided by Rust's ownership system. The crate in question is designed to facilitate lazy initialization patterns in concurrent environments, but the implementation contains a fundamental flaw in how it handles types that are not Send but are Sync.
The technical root cause of this vulnerability lies in the improper handling of thread crossing scenarios within the conquer-once implementation. Specifically, when a type that implements Sync but not Send is used with this crate, the system fails to properly enforce the safety constraints that Rust's type system should provide. This creates a situation where data that should remain isolated to a single thread can be accessed concurrently across thread boundaries, leading to undefined behavior and potential memory corruption. The flaw manifests when the crate attempts to move a non-Send type between threads, violating Rust's fundamental safety guarantees.
From an operational perspective, this vulnerability presents a significant risk to applications that rely on the conquer-once crate for lazy initialization in multi-threaded contexts. Memory corruption resulting from this flaw can lead to application crashes, data corruption, or potentially exploitable conditions that could allow attackers to execute arbitrary code. The impact is particularly severe because the vulnerability occurs at runtime during concurrent access patterns rather than at compile time, making it difficult to detect through static analysis alone. The flaw essentially allows for a form of data race that bypasses Rust's memory safety mechanisms, creating a vector for both accidental bugs and potential malicious exploitation.
The vulnerability aligns with CWE-416, which deals with use after free conditions, and relates to broader categories of memory safety violations in concurrent systems. It also maps to ATT&CK technique T1059.007 for command and scripting interpreter, as memory corruption could potentially lead to code execution scenarios. The issue demonstrates how even well-intentioned concurrency utilities can introduce security vulnerabilities when they fail to properly respect Rust's safety guarantees. Organizations using this crate should immediately upgrade to version 0.3.2 or later, which implements proper synchronization mechanisms to prevent thread crossing for non-Send types. Additionally, developers should conduct thorough code reviews of any custom implementations that rely on similar patterns, ensuring that proper synchronization primitives are used when dealing with potentially unsafe concurrent access patterns. The fix implemented in version 0.3.2 addresses the core issue by ensuring that types that are not Send cannot be safely moved between threads, thereby maintaining Rust's memory safety guarantees in concurrent contexts.