Summary
PyO3 has a missing Sync bound on PyCFunction::new_closure closures
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.
Impact
Multiple concurrent operations access a shared resource without proper synchronization, producing unpredictable results depending on timing. Typical impact: TOCTOU exploits, data corruption, or privilege escalation.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Frequently Asked Questions
- What is GHSA-CHGR-C6PX-7XPP? GHSA-CHGR-C6PX-7XPP is a medium-severity race condition vulnerability in pyo3 (rust), affecting versions < 0.29.0. It is fixed in 0.29.0. Multiple concurrent operations access a shared resource without proper synchronization, producing unpredictable results depending on timing.
- Which versions of pyo3 are affected by GHSA-CHGR-C6PX-7XPP? pyo3 (rust) versions < 0.29.0 is affected.
- Is there a fix for GHSA-CHGR-C6PX-7XPP? Yes. GHSA-CHGR-C6PX-7XPP is fixed in 0.29.0. Upgrade to this version or later.
- Is GHSA-CHGR-C6PX-7XPP exploitable, and should I be worried? Whether GHSA-CHGR-C6PX-7XPP is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether GHSA-CHGR-C6PX-7XPP is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix GHSA-CHGR-C6PX-7XPP? Upgrade
pyo3to 0.29.0 or later.