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RUSTSEC-2026-0221: event-listener allows !Send tags to cross thread boundaries via StackSlot #685

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Package event-listener
Version 5.4.1
Warning unsound
URL smol-rs/event-listener#163
Patched Versions >=5.4.2
Unaffected Versions <5.1.0

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.

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