RUSTSEC-2026-0221 `event-listener` allows `!Send` tags to cross thread boundaries via `StackSlot`
Not scored
Published
Check this codebase for RUSTSEC-2026-0221 and fix it if it is affected.
What it is: RUSTSEC-2026-0221 is a vulnerability in event-listener, published on 13 Jul 2026.
Exploitation: There is no known exploitation of RUSTSEC-2026-0221 in the wild and no public exploit code.
Affected packages and fixed versions:
- event-listener (crates.io): affected from 5.1.0; fixed in 5.4.2
Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.
Reference: https://insights.sbomify.com/RUSTSEC-2026-0221/ (Markdown: https://insights.sbomify.com/RUSTSEC-2026-0221/index.md)
The event-listener library allows unsafe thread boundary crossings for non-Send types, causing data races in safe code.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Not stated
- Victim action needed
- Not needed
- Fix
- Available
What is RUSTSEC-2026-0221?
RUSTSEC-2026-0221 is a vulnerability in event-listener, published on 13 Jul 2026.
Official 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.
Which versions are affected by RUSTSEC-2026-0221?
1 open source package ship an affected version, including event-listener.
| Package | Affected | Fixed in |
|---|---|---|
event-listener crates.io | From 5.1.0 | 5.4.2 |
How do I fix RUSTSEC-2026-0221?
Upgrade event-listener to 5.4.2 or later.
Is RUSTSEC-2026-0221 being exploited?
There is no known exploitation of RUSTSEC-2026-0221 in the wild and no public exploit code.