{"id":"GHSA-36hh-v3qg-5jq4","title":"PyO3 has an Out-of-bounds Read in `nth` / `nth_back` for `PyList` and `PyTuple` iterators","summary":"PyO3 has an Out-of-bounds Read in `nth` / `nth_back` for `PyList` and `PyTuple` iterators","severity":"high","cwe":["CWE-125"],"vendor":"pyo3","product":"pyo3","ecosystem":"rust","affected":["pyo3 < 0.29.0"],"patched":["pyo3 0.29.0"],"published":"2026-06-12","updated":"2026-06-12","source":"GHSA","sourceUrl":"https://github.com/advisories/GHSA-36hh-v3qg-5jq4","references":[{"url":"https://github.com/PyO3/pyo3/pull/6086"},{"url":"https://rustsec.org/advisories/RUSTSEC-2026-0176.html"},{"url":"https://github.com/advisories/GHSA-36hh-v3qg-5jq4"}],"tags":["ghsa","rust"],"ingestedAt":"2026-07-07T15:41:59.019Z","slug":"GHSA-36hh-v3qg-5jq4","body":"## Overview\n\nPyO3 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.\n\n## Affected packages\n\n- `pyo3 < 0.29.0`\n\n## Remediation\n\nUpgrade to a patched release:\n\n- `pyo3 0.29.0`","depth":"twilight","depthScore":41,"depthScoreParts":{"impact":41.3,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}