RUSTSEC-2020-0087: 
Rust vulnerability analysis and mitigation

An issue was discovered in the try-mutex crate versions before 0.3.0 for Rust programming language. The vulnerability was identified and assigned CVE-2020-35924, with the discovery being reported on November 16, 2020. The vulnerability stems from TryMutex implementation that incorrectly allows cross-thread sending of a non-Send type, which could lead to potential security issues in Rust applications using this crate (RustSec Advisory).

The technical issue lies in the TryMutex implementation which implements Sync for all types T without proper bounds. The vulnerability occurs because TryMutex should have been bounded by T: Send, similar to the standard library's Mutex implementation. The severity of this vulnerability has been assessed with a CVSS v3.1 Base Score of 5.5 (Medium), with the vector string CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H. The vulnerability has been classified under CWE-787 (Out-of-bounds Write) (NVD Database).

The vulnerability allows for the unsafe transmission of non-Send types across thread boundaries, which can lead to data races in safe Rust code. This is particularly concerning as it bypasses Rust's core safety guarantees regarding thread safety. For example, it enables smuggling of non-Send types like Rc (Reference Counted smart pointer) across thread boundaries, which could result in memory corruption or undefined behavior (GitHub Issue).

The vulnerability can be exploited in safe Rust code without requiring unsafe blocks. A proof of concept demonstrates the ability to send an Rc (Reference Counted) type across thread boundaries, which should not be possible in safe Rust code. The exploit has been documented and demonstrated by the Rust security research group at Georgia Tech (GitHub Issue).

The vulnerability has been fixed in version 0.3.0 of the try-mutex crate. Users are advised to upgrade to this version or later to resolve the security issue. If immediate upgrade is not possible, users should audit their code for any cross-thread usage of TryMutex with non-Send types (RustSec Advisory).