Rust advisories / event-listener
UnsoundRUSTSEC-2026-0221 · event-listener
RUSTSEC-2026-0221: `event-listener` allows `!Send` tags to cross thread boundaries via `StackSlot`
Short answerevent-listener has an API that can cause undefined behaviour from safe code: `event-listener` allows `!Send` tags to cross thread boundaries via `StackSlot`. Fixed in 5.4.2.
| Crate | event-listener |
|---|---|
| Type | Unsound (memory-corruption, thread-safety) |
| Affected versions | From 5.1.0 before 5.4.2. |
| Fixed in | 5.4.2 |
| Severity | not scored |
| Published | 2026-07-13 |
| Last changed | 2026-07-31 |
| Also known as | none |
What to do
- See which version you have:
cargo tree -i event-listener(it also shows which of your dependencies pulls it in). - Update within your version requirement:
cargo update -p event-listener. If the fix is a newer major or minor than your requirement allows, raise it in Cargo.toml (for exampleevent-listener = "5.4.2") or update the dependency that pulls it in. - Check again with
cargo audit, or paste your Cargo.lock into our Cargo.toml checker.
Details from the advisory
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.
References
- Package: crates.io/crates/event-listener
- Advisory: rustsec.org/advisories/RUSTSEC-2026-0221.html
- Web: github.com/smol-rs/event-listener/pull/163
From the RustSec Advisory Database (CC0-1.0) via the OSV export, downloaded Oct 24, 2026. Severity score computed from the published CVSS vector.
Up next
Same crateevent-listener: security historyEvery advisory for this crate, and whether it is safe to use today.Read it next →Did this answer your question?