PyO3 has an Out-of-bounds Read in nth / nth_back for PyList and PyTuple iterators

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

8.7 · 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 · score source

EPSS

No dated EPSS signal available.

As published by the source; long descriptions are shortened.

PyO3 0.24.0 added optimized implementations of Iterator::nth and DoubleEndedIterator::nthback 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 getitemunchecked. 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 nthback 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.

Published by the source

12 Jun 2026, 19:32 UTC

Last modified by the source

12 Jun 2026, 19:32 UTC

Source last checked

26 Oct 2026, 15:42 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-36hh-v3qg-5jq4

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# Patch Next advisory brief: GHSA-36hh-v3qg-5jq4

Advisory: PyO3 has an Out-of-bounds Read in `nth` / `nth_back` for `PyList` and `PyTuple` iterators
IDs: GHSA-36hh-v3qg-5jq4
Record: https://patchnext.com/advisories/ghsa-36hh-v3qg-5jq4 (revision 1, source checked 26 Oct 2026, 15:42 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.7)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: pyo3 0.29.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- crates.io pyo3: affected < 0.29.0; fixed in 0.29.0

## Suggested inspection (read-only)
- crates.io pyo3: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on pyo3.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-36hh-v3qg-5jq4 (GitHub-reviewed advisory GHSA-36hh-v3qg-5jq4 lists affected ranges: crates.io pyo3 >=0 <0.29.0)

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