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medium —

GHSA-chgr-c6px-7xpp json

PyO3 has a missing `Sync` bound on `PyCFunction::new_closure` closures

published 5mo ago modified 2mo ago also RUSTSEC-2026-0177

cvss
—
not scored
cisa kev
Not listed
not in CISA's catalog
epss
—
no score, EPSS covers CVEs only
public exploits
0
none known

Summary

`PyCFunction::new_closure` (and the temporary `new_closure_bound` complement in the 0.21–0.22 series) required the supplied closure to be `Send + 'static` but not `Sync`. The resulting `PyCFunction` is a Python callable that can be invoked from any Python thread, which means the closure may be called concurrently from multiple threads, and needs a `Sync` bound to prevent possible data races.

The problem exists under all Python versions but is particularly vulnerable under the newer free-threaded Python variant, which do not have serial execution imposed by the Global Interpreter Lock. Under releases protected by the GIL, the ability to "detach" from the Python interpreter temporarily inside the closure (e.g. by `Python::detach`) makes it possible for interleaved and/or concurrent execution of various portions of the closure.

PyO3 0.29.0 added a `Sync` bound to close this thread-safety bug.

Patch / fix

  • crates.io pyo3 0.29.0

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Affected packages

ecosystem package affected fixed in
crates.io pyo3
<0.29.0
>=0.0.0-0, <0.29.0
0.29.0

Classification

Weakness
  • CWE-362 Concurrent Execution using Shared Resource with Improper Synchronization

References

Sources

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