# RUSTSEC-2026-0186: Unchecked pointer offset in crate `memmap2`

> Attackers can trigger undefined behavior and potential crashes by passing invalid offsets to memory mapping functions in the memmap2 Rust library.

- **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:** 20 Jun 2026

## What is RUSTSEC-2026-0186?

RUSTSEC-2026-0186 is a vulnerability in memmap2, published on 20 Jun 2026. 

### Official description

Affected versionf of `memmap2` did not perform enough validation on the `offset` and `len` parameters of
`Mmap::[unchecked_]advise_range()`,
`MmapMut::[unchecked_]advise_ranage()`
and `MmapMut::flush[_async]_range()`.

This can cause undefined behavior due to invalid values being passed to [`pointer::offset()`] and [`pointer::add()`]
when passing an out-of-bounds range to any of the affected functions.

The flaw was corrected in commit [`cee7cf0`] and released in version `0.9.11`.

The invalid pointer is not dereferenced,
but it is passed to the `madvise` and `msync` syscalls and their Windows equivalents.

[`pointer::offset()`]: https://doc.rust-lang.org/stable/std/primitive.pointer.html#method.offset-1
[`pointer::add()`]: https://doc.rust-lang.org/stable/std/primitive.pointer.html#method.add-1
[`cee7cf0`] https://github.com/RazrFalcon/memmap2-rs/pull/170/changes/cee7cf03a9ee095982a3c37b7aac8e3f68f1a00c

## Which versions are affected by RUSTSEC-2026-0186?

1 open source package ship an affected version, including memmap2.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `memmap2` | crates.io | From 0.0.0-0 | 0.9.11 |

## How do I fix RUSTSEC-2026-0186?

Upgrade memmap2 to 0.9.11 or later.

## Is RUSTSEC-2026-0186 being exploited?

There is no known exploitation of RUSTSEC-2026-0186 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for RUSTSEC-2026-0186 and fix it if it is affected.

What it is: RUSTSEC-2026-0186 is a vulnerability in memmap2, published on 20 Jun 2026. 
Exploitation: There is no known exploitation of RUSTSEC-2026-0186 in the wild and no public exploit code.

Affected packages and fixed versions:
- memmap2 (crates.io): affected from 0.0.0-0; fixed in 0.9.11

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/RUSTSEC-2026-0186/ (Markdown: https://insights.sbomify.com/RUSTSEC-2026-0186/index.md)
```

## Sources

- OSV: https://osv.dev/vulnerability/RUSTSEC-2026-0186

---
From sbomify Insights: https://insights.sbomify.com/RUSTSEC-2026-0186/
Summaries are generated and may contain mistakes; the official description above is the record.