GHSA-CHGR-C6PX-7XPP

Vulnerability from github – Published: 2026-06-12 20:09 – Updated: 2026-06-12 20:09
VLAI
Summary
PyO3 has a missing `Sync` bound on `PyCFunction::new_closure` closures
Details

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.

Severity
6.3 (Medium)
CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:L/VI:L/VA:L/SC:N/SI:N/SA:N
Show details on source website
To clipboard 

{
  "affected": [
    {
      "package": {
        "ecosystem": "crates.io",
        "name": "pyo3"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "0.29.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [],
  "database_specific": {
    "cwe_ids": [
      "CWE-362"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-06-12T20:09:05Z",
    "nvd_published_at": null,
    "severity": "MODERATE"
  },
  "details": "`PyCFunction::new_closure` (and the temporary `new_closure_bound` complement in the 0.21\u20130.22 series) required the supplied closure to be `Send + \u0027static` 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.\n\nThe 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.\n\nPyO3 0.29.0 added a `Sync` bound to close this thread-safety bug.",
  "id": "GHSA-chgr-c6px-7xpp",
  "modified": "2026-06-12T20:09:05Z",
  "published": "2026-06-12T20:09:05Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/PyO3/pyo3/pull/6096"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/PyO3/pyo3"
    },
    {
      "type": "WEB",
      "url": "https://github.com/PyO3/pyo3/releases/tag/v0.29.0"
    },
    {
      "type": "WEB",
      "url": "https://rustsec.org/advisories/RUSTSEC-2026-0177.html"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:L/VI:L/VA:L/SC:N/SI:N/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "PyO3 has a missing `Sync` bound on `PyCFunction::new_closure` closures"
}


Log in or create an account to share your comment.




Tags
Taxonomy of the tags.





Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

Author Source Type Date Other

Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.


Detection rules are retrieved from Rulezet.