# CVE-2026-47261: Wasmtime: WASI path_open(TRUNCATE) bypasses `FilePerms::WRITE` host restriction

> Attackers can bypass read-only file restrictions in Wasmtime WASI embeddings by using the TRUNCATE flag, allowing unauthorized file modification.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 15 Jun 2026
- **Updated:** 16 Jun 2026
- **Also known as:** DEBIAN-CVE-2026-47261, GHSA-2r75-cxrj-cmph, JLSEC-2026-1366, RUSTSEC-2026-0149, UBUNTU-CVE-2026-47261

## What is CVE-2026-47261?

CVE-2026-47261 is a high-severity vulnerability in bytecodealliance wasmtime, published on 15 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Wasmtime is a runtime for WebAssembly. In versions prior to 24.0.9, 36.0.10, and 44.0.2, when a filesystem preopen is given DirPerms::all() and FilePerms::READ without FilePerms::WRITE, this access control mechanism can be bypassed via the wasip2 descriptor.open-at or wasip1 path_open interfaces by opening a file with only the OpenFlags::TRUNCATE oflag. The root cause is that the clause handling OpenFlags::TRUNCATE in crates/wasi/src/filesystem.rs (Dir::open_at, lines 967–969) did not set open_mode |= OpenMode::WRITE;, which is later used for the access control check against FilePerms to determine whether opening the file is permitted; the single-line fix adds that missing assignment, after which the affected calls correctly fail with error-code.not-permitted and ERRNO_PERM respectively. Only wasmtime-wasi embeddings that combine DirPerms::MUTATE with FilePerms::READ are affected by this bug. In particular, the Wasmtime project's wasmtime-cli's use of wasmtime-wasi is not affected, because it always sets FilePerms::all() for all preopens. This issue has been fixed in versions 24.0.9, 36.0.10 and44.0.2.

Weakness: CWE-284 (Improper Access Control)

## Which versions are affected by CVE-2026-47261?

7 open source packages ship an affected version, including wasmtime-wasi. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `wasmtime-wasi` | crates.io | All versions | 24.0.9 |
| `wasmtime-wasi` | crates.io | All versions | 24.0.9 |
| `wasmtime-wasi` | crates.io | From 0.0.0-0 | 24.0.9, 36.0.10, 44.0.2, 45.0.0 |
| `wasmtime-wasi` | crates.io | From 25.0.0 | 36.0.10 |
| `wasmtime-wasi` | crates.io | From 25.0.0 | 36.0.10 |
| `wasmtime-wasi` | crates.io | From 37.0.0 | 44.0.2 |
| `wasmtime-wasi` | crates.io | From 37.0.0 | 44.0.2 |

Products: Bytecodealliance Wasmtime.

## How do I fix CVE-2026-47261?

Upgrade wasmtime-wasi to a fixed version for your release line: 24.0.9, 36.0.10, 44.0.2 or 45.0.0.

## Is CVE-2026-47261 being exploited?

There is no known exploitation of CVE-2026-47261 in the wild and no public exploit code.

## Other vulnerabilities in bytecodealliance wasmtime

- [CVE-2026-34971](https://insights.sbomify.com/CVE-2026-34971/): Wasmtime miscompiled guest heap access enables sandbox escape on aarch64 Cranelift (critical 9.0)
- [CVE-2026-34987](https://insights.sbomify.com/CVE-2026-34987/): Wasmtime with Winch compiler backend on aarch64 may allow a sandbox-escaping memory access (critical 9.0)
- [CVE-2022-39393](https://insights.sbomify.com/CVE-2022-39393/): Wasmtime vulnerable to data leakage between instances in the pooling allocator (high 8.6)
- [CVE-2022-24791](https://insights.sbomify.com/CVE-2022-24791/): Use after free in Wasmtime (high 8.1)
- [CVE-2026-34941](https://insights.sbomify.com/CVE-2026-34941/): Wasmtime has a Heap OOB read in component model UTF-16 to latin1+utf16 string transcoding (medium 6.9)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-47261 and fix it if it is affected.

What it is: CVE-2026-47261 is a high-severity vulnerability in bytecodealliance wasmtime, published on 15 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-47261 in the wild and no public exploit code.

Affected packages and fixed versions:
- wasmtime-wasi (crates.io): affected all versions; fixed in 24.0.9
- wasmtime-wasi (crates.io): affected all versions; fixed in 24.0.9
- wasmtime-wasi (crates.io): affected from 0.0.0-0; fixed in 24.0.9, 36.0.10, 44.0.2, 45.0.0
- wasmtime-wasi (crates.io): affected from 25.0.0; fixed in 36.0.10
- wasmtime-wasi (crates.io): affected from 25.0.0; fixed in 36.0.10
- wasmtime-wasi (crates.io): affected from 37.0.0; fixed in 44.0.2
- wasmtime-wasi (crates.io): affected from 37.0.0; fixed in 44.0.2

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/CVE-2026-47261/ (Markdown: https://insights.sbomify.com/CVE-2026-47261/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-47261
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-47261
- OSV: https://osv.dev/vulnerability/CVE-2026-47261

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-47261/
Summaries are generated and may contain mistakes; the official description above is the record.