{"id":"GHSA-36hh-v3qg-5jq4","aliases":["RUSTSEC-2026-0176"],"status":"published","title":"PyO3 has an Out-of-bounds Read in `nth` / `nth_back` for `PyList` and `PyTuple` iterators","description":"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.","severity":{"version":"4.0","score":8.7,"vector":"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","level":"high","from":"ghsa"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":true},"cwes":["CWE-125"],"published":"2026-06-11T12:00:00Z","modified":"2026-09-10T03:51:07Z","fixes":[{"ecosystem":"crates.io","package":"pyo3","fixed_in":["0.29.0"],"sources":["ghsa","osv"]}],"affected":[{"source":"ghsa","ecosystem":"crates.io","package":"pyo3","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"0.29.0"}]}]},{"source":"osv","ecosystem":"crates.io","package":"pyo3","ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"0.29.0"}]}]},{"source":"osv","ecosystem":"crates.io","package":"pyo3","ranges":[{"type":"SEMVER","events":[{"introduced":"0.24.0"},{"fixed":"0.29.0"}]}]}],"references":[{"url":"https://github.com/PyO3/pyo3/pull/6086","tags":["web"]},{"url":"https://rustsec.org/advisories/RUSTSEC-2026-0176.html","tags":["web","advisory"]},{"url":"https://github.com/advisories/GHSA-36hh-v3qg-5jq4"},{"url":"https://github.com/PyO3/pyo3","tags":["package"]},{"url":"https://crates.io/crates/pyo3","tags":["package"]}],"sources":{"ghsa":[{"id":"GHSA-36hh-v3qg-5jq4","title":"PyO3 has an Out-of-bounds Read in `nth` / `nth_back` for `PyList` and `PyTuple` iterators","description":"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.","status":"published","published":"2026-06-12T19:32:47Z","modified":"2026-06-12T19:32:49Z","cvss":[{"version":"4.0","score":8.7,"vector":"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","level":"high"}],"cwes":["CWE-125"],"updated_at":"2026-11-02T14:40:27.329706Z"}],"osv":[{"id":"GHSA-36hh-v3qg-5jq4","title":"PyO3 has an Out-of-bounds Read in `nth` / `nth_back` for `PyList` and `PyTuple` iterators","description":"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.","status":"published","published":"2026-06-12T19:32:47Z","modified":"2026-09-10T03:51:07.658803617Z","cvss":[{"version":"4.0","score":8.7,"vector":"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","level":"high"}],"cwes":["CWE-125"],"updated_at":"2026-11-02T15:46:35.406455Z"},{"id":"RUSTSEC-2026-0176","title":"Out-of-bounds read in `nth` / `nth_back` for `PyList` and `PyTuple` iterators","description":"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.","status":"published","published":"2026-06-11T12:00:00Z","modified":"2026-06-13T06:30:04.39857288Z","updated_at":"2026-11-02T15:53:40.430679Z"}]}}