Reported

July 13, 2026

Issued

July 31, 2026

Package

event-listener (crates.io)

Type

INFO Unsound

Categories

• memory-corruption
• thread-safety

Keywords

#concurrency

References

• https://github.com/smol-rs/event-listener/pull/163

Patched

• >=5.4.2

Unaffected

• <5.1.0

Description

Affected versions of event-listener unconditionally implement Send and Sync for StackSlot<'_, T>, the stack-allocated listener type created by the listener! macro.

This allows a !Send tag type set via Event::with_tag to be moved to another thread and accessed via StackSlot::wait, causing a data race in safe code.

Advisory available under CC0-1.0 license.