# Wasmtime-WASI filesystem sandbox escape with symlink rename

Source: https://junglewise.ai/threats/rustsec-2026-0352-filesystem-sandbox-escape-when-renaming-symlinks-with-86b22c86  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-10-14. Updated: 2026-10-16  
License: CC BY 4.0 with a link back

Severity: medium · CVSS 4 · Published 2026-10-14

Wasmtime-WASI is a runtime library that provides sandboxed filesystem access for WebAssembly programs. A vulnerability in symlink handling allows an attacker with authenticated access to escape the sandbox and access files outside the intended restricted directory by renaming symlinks with trailing slashes. This could lead to unauthorized data access or modification on affected macOS and FreeBSD systems.

Technologies: [Bytecode Alliance Wasmtime-Wasi](https://junglewise.ai/threats/technologies/bytecode-alliance-wasmtime-wasi), [wasmtime-wasi (crates.io)](https://junglewise.ai/threats/technologies/wasmtime-wasi). Vendors: [Bytecode Alliance](https://junglewise.ai/threats/vendors/bytecode-alliance), [crates.io](https://junglewise.ai/threats/vendors/crates-io).

## Quick answers

**Is This vulnerability exploited in the wild?** No. Junglewise Threat Intelligence has no report of This vulnerability being exploited in the wild.

**How severe is This vulnerability?** Medium severity, with a CVSS score of 4, published 14 October 2026.

**Which products and versions are affected?** Bytecode Alliance Wasmtime-Wasi before 36.0.18, 37.0.0 before 48.0.6, 49.0.0 before 49.0.3; wasmtime-wasi (crates.io) SEMVER:introduced=0.0.0-0,fixed=36.0.18,introduced=37.0.0,fixed=48.0.6,introduced=49.0.0,fixed=49.0.3.

**Is there a fix for This vulnerability?** Yes. wasmtime-wasi (crates.io): upgrade to 49.0.3 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is This vulnerability attacked?** It is attacked over the network, in a software library.

**Am I affected?** Check whether you run Bytecode Alliance Wasmtime-Wasi or wasmtime-wasi (crates.io) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- wasmtime-wasi (crates.io): upgrade to 49.0.3 or later

  ```sh
  cargo update -p wasmtime-wasi
  ```


## Technical details

The vulnerability is a filesystem sandbox escape in the wasmtime-wasi library affecting symlink rename operations on macOS and FreeBSD. An authenticated attacker using the WASI filesystem interface can bypass path restrictions by crafting a rename operation involving a symlink with a trailing slash, allowing them to access or modify files outside the sandbox boundary.

## Affected products

- Bytecode Alliance wasmtime-wasi before 36.0.18, 37.0.0 before 48.0.6, 49.0.0 before 49.0.3

## Identifiers

- GHSA-m9f7-9w4p-gv38
- RUSTSEC-2026-0352

## Timeline

- 2026-10-14: disclosed

## References

- [https://crates.io/crates/wasmtime-wasi](https://crates.io/crates/wasmtime-wasi)
- [https://rustsec.org/advisories/RUSTSEC-2026-0352.html](https://rustsec.org/advisories/RUSTSEC-2026-0352.html)

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