{"id":"RUSTSEC-2026-0176","summary":"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\n`DoubleEndedIterator::nth_back` for the `BoundListIterator` and\n`BoundTupleIterator` types. These implementations computed the target index\nusing unchecked `usize` addition (`index + n`) before bounds-checking against\nthe sequence length, then read the element via `get_item_unchecked`.\n\nIn `nth` methods, a sufficiently large `n` (combined with a non-zero internal\nindex) could cause the addition to overflow and wrap around, producing a small\n\"target index\" that passed the bounds check and enabling reads at the front\nof 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\nsimilar fashion, however would instead allow reads of arbitrary memory past\nthe end of the `list` or `tuple` storage.\n\nPyO3 0.29.0 has corrected these methods to use checked arithmetic at the\npositions which could be at risk of overflow.","aliases":["GHSA-36hh-v3qg-5jq4"],"modified":"2026-06-13T06:30:04.398572880Z","published":"2026-06-11T12:00:00Z","database_specific":{"license":"CC0-1.0"},"references":[{"type":"PACKAGE","url":"https://crates.io/crates/pyo3"},{"type":"ADVISORY","url":"https://rustsec.org/advisories/RUSTSEC-2026-0176.html"},{"type":"WEB","url":"https://github.com/PyO3/pyo3/pull/6086"}],"affected":[{"package":{"name":"pyo3","ecosystem":"crates.io","purl":"pkg:cargo/pyo3"},"ranges":[{"type":"SEMVER","events":[{"introduced":"0.24.0"},{"fixed":"0.29.0"}]}],"ecosystem_specific":{"affected_functions":null,"affects":{"arch":[],"os":[],"functions":["pyo3::types::list::BoundListIterator::nth","pyo3::types::list::BoundListIterator::nth_back","pyo3::types::tuple::BoundTupleIterator::nth","pyo3::types::tuple::BoundTupleIterator::nth_back"]}},"database_specific":{"categories":["memory-exposure"],"cvss":null,"informational":null,"source":"https://github.com/rustsec/advisory-db/blob/osv/crates/RUSTSEC-2026-0176.json"}}],"schema_version":"1.7.5"}