RUSTSEC-2020-0061: futures_task::noop_waker_ref can segfault due to dereferencing a NULL pointer

What to do

1. See which version you have: cargo tree -i futures-task (it also shows which of your dependencies pulls it in).
2. Update within your version requirement: cargo update -p futures-task. If the fix is a newer major or minor than your requirement allows, raise it in Cargo.toml (for example futures-task = "0.3.5") or update the dependency that pulls it in.
3. Check again with cargo audit, or paste your Cargo.lock into our Cargo.toml checker.

Details from the advisory

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.

References

• Package: crates.io/crates/futures-task
• Advisory: rustsec.org/advisories/RUSTSEC-2020-0061.html
• Report: github.com/rust-lang/futures-rs/issues/2091

From the RustSec Advisory Database (CC0-1.0) via the OSV export, downloaded Oct 24, 2026. Severity score computed from the published CVSS vector.

Other advisories for futures-task

• Vulnerability HighRUSTSEC-2020-0060 · 2020-09-04futures_task::waker may cause a use-after-free if used on a type that isn't 'static

Full security history of futures-task