RUSTSEC-2020-0061

futures_task::noop_waker_ref can segfault due to dereferencing a NULL pointer

Reported

May 3, 2020

Issued

October 31, 2020 (last modified: October 19, 2021)

Package

futures-task (crates.io)

Type

Vulnerability

Categories

denial-of-service

Keywords

#NULL-pointer-dereference #memory-management

Aliases

CVE-2020-35907

Details

https://github.com/rust-lang/futures-rs/issues/2091

CVSS Score

5.5 MEDIUM

CVSS Details

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

CVSS Vector

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

Patched

>=0.3.5

Affected Functions

Version

futures_task::noop_waker_ref

>=0.3.0

Description

Affected versions of the crate used a UnsafeCell in thread-local storage to return a noop waker reference, assuming that the reference would never be returned from another thread.

This resulted in a segmentation fault crash if Waker::wake_by_ref() was called on a waker returned from another thread due to it attempting to dereference a pointer that wasn't accessible from the main thread.

Reproduction Example (from issue):

use futures_task::noop_waker_ref;
fn main() {
    let waker = std::thread::spawn(|| noop_waker_ref()).join().unwrap();
    waker.wake_by_ref();
}

The flaw was corrected by using a OnceCell::Lazy<> wrapper around the noop waker instead of thread-local storage.