# GHSA-36hh-v3qg-5jq4: Out-of-bounds read in `nth` / `nth_back` for `PyList` and `PyTuple` iterators

> Integer overflow in PyO3 iterators allows out-of-bounds memory reads, potentially exposing sensitive data or causing crashes.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Not stated
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 11 Jun 2026
- **Also known as:** RUSTSEC-2026-0176

## What is GHSA-36hh-v3qg-5jq4?

GHSA-36hh-v3qg-5jq4 is a vulnerability in pyo3, published on 11 Jun 2026. 

### Official 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`.

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.

PyO3 0.29.0 has corrected these methods to use checked arithmetic at the
positions which could be at risk of overflow.

## Which versions are affected by GHSA-36hh-v3qg-5jq4?

3 open source packages ship an affected version, including pyo3.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `pyo3` | crates.io | All versions | 0.29.0 |
| `pyo3` | crates.io | All versions | 0.29.0 |
| `pyo3` | crates.io | From 0.24.0 | 0.29.0 |

## How do I fix GHSA-36hh-v3qg-5jq4?

Upgrade pyo3 to 0.29.0 or later.

## Is GHSA-36hh-v3qg-5jq4 being exploited?

There is no known exploitation of GHSA-36hh-v3qg-5jq4 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for GHSA-36hh-v3qg-5jq4 and fix it if it is affected.

What it is: GHSA-36hh-v3qg-5jq4 is a vulnerability in pyo3, published on 11 Jun 2026. 
Exploitation: There is no known exploitation of GHSA-36hh-v3qg-5jq4 in the wild and no public exploit code.

Affected packages and fixed versions:
- pyo3 (crates.io): affected all versions; fixed in 0.29.0
- pyo3 (crates.io): affected all versions; fixed in 0.29.0
- pyo3 (crates.io): affected from 0.24.0; fixed in 0.29.0

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/GHSA-36hh-v3qg-5jq4/ (Markdown: https://insights.sbomify.com/GHSA-36hh-v3qg-5jq4/index.md)
```

## Sources

- OSV: https://osv.dev/vulnerability/GHSA-36hh-v3qg-5jq4

---
From sbomify Insights: https://insights.sbomify.com/GHSA-36hh-v3qg-5jq4/
Summaries are generated and may contain mistakes; the official description above is the record.