RUSTSEC-2020-0059

MutexGuard::map can cause a data race in safe code

Reported

October 22, 2020

Issued

October 30, 2020 (last modified: October 19, 2021)

Package

futures-util (crates.io)

Type

Vulnerability

Categories

thread-safety

Keywords

#concurrency #memory-corruption #memory-management

Aliases

CVE-2020-35905

Details

https://github.com/rust-lang/futures-rs/issues/2239

CVSS Score

4.7 MEDIUM

CVSS Details

Attack vector: Local
Attack complexity: High
Privileges required: Low
User interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: None
Availability: High

CVSS Vector

CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H

Patched

>=0.3.7

Unaffected

<0.3.2

Affected Functions

Version

futures_util::lock::MutexGuard::map

>=0.3.2

Description

Affected versions of the crate had a Send/Sync implementation for MappedMutexGuard that only considered variance on T, while MappedMutexGuard dereferenced to U.

This could of led to data races in safe Rust code when a closure used in MutexGuard::map() returns U that is unrelated to T.

The issue was fixed by fixing Send and Sync implementations, and by adding a PhantomData<&'a mut U> marker to the MappedMutexGuard type to tell the compiler that the guard is over U too.