GHSA-36HH-V3QG-5JQ4

Vulnerability from github – Published: 2026-06-12 19:32 – Updated: 2026-06-12 19:32
VLAI
Summary
PyO3 has an Out-of-bounds Read in `nth` / `nth_back` for `PyList` and `PyTuple` iterators
Details

PyO3 0.24.0 added optimized implementations of Iterator::nth and DoubleEndedIterator::nth_back for the BoundListIterator and BoundTupleIterator types. These implementations computed the target index using unchecked usize addition (index + n) before bounds-checking against the sequence length, then read the element via get_item_unchecked.

In nth methods, a sufficiently large n (combined with a non-zero internal index) could cause the addition to overflow and wrap around, producing a small "target index" that passed the bounds check and enabling reads at the front of the list or tuple of elements previously yielded by the iterator.

In nth_back methods, a sufficiently large n could cause underflow in a similar fashion, however would instead allow reads of arbitrary memory past the end of the list or tuple storage.

Severity
8.7 (High)
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N
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{
  "affected": [
    {
      "package": {
        "ecosystem": "crates.io",
        "name": "pyo3"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "0.29.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [],
  "database_specific": {
    "cwe_ids": [
      "CWE-125"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-06-12T19:32:47Z",
    "nvd_published_at": null,
    "severity": "HIGH"
  },
  "details": "PyO3 0.24.0 added optimized implementations of `Iterator::nth` and `DoubleEndedIterator::nth_back` for the `BoundListIterator` and `BoundTupleIterator` types. These implementations computed the target index using unchecked `usize` addition (`index + n`) before bounds-checking against the sequence length, then read the element via `get_item_unchecked`.\n\nIn `nth` methods, a sufficiently large `n` (combined with a non-zero internal index) could cause the addition to overflow and wrap around, producing a small \"target index\" that passed the bounds check and enabling reads at the front of the `list` or `tuple` of elements previously yielded by the iterator.\n\nIn `nth_back` methods, a sufficiently large `n` could cause underflow in a similar fashion, however would instead allow reads of arbitrary memory past the end of the `list` or `tuple` storage.",
  "id": "GHSA-36hh-v3qg-5jq4",
  "modified": "2026-06-12T19:32:47Z",
  "published": "2026-06-12T19:32:47Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/PyO3/pyo3/pull/6086"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/PyO3/pyo3"
    },
    {
      "type": "WEB",
      "url": "https://rustsec.org/advisories/RUSTSEC-2026-0176.html"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "PyO3 has an Out-of-bounds Read in `nth` / `nth_back` for `PyList` and `PyTuple` iterators"
}


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