AIKIDO-2026-561892
greenlet is vulnerable to Use After Free
20
Low Risk
This Affects:
greenletTL;DR
On free-threaded (no-GIL) builds of CPython, greenlet's saved C-stack state could become inconsistent if the garbage collector ran while a greenlet was suspended, leading to a use-after-free and interpreter crash. A related issue could deadlock the interpreter if a greenlet switch happened while a critical section lock was held.
Who does this affect?
You are affected only if you run a free-threaded (no-GIL) build of CPython 3.14 or newer and use greenlet-based libraries (such as gevent or Playwright's sync API) under garbage-collector pressure; this can cause unpredictable crashes or, less commonly, a deadlock. Standard GIL-enabled CPython builds are not affected.
Background info
greenlet is vulnerable to Use After Free in versions 3.3.0 - 3.5.3.
How to fix this
Upgrade the greenlet library to the patch version.
Are You Affected?
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