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🛡️ CVE-2026-47261 — wasmtime

🟠 CVSS 8.0 — High ✅ No Known Exploit CWE-284 NVD
8.0
CVSS Score
0 Low4 Medium7 High9 Critical10

Description

wasmtime-wasi: WASI path_open(TRUNCATE) bypasses FilePerms::WRITE host restriction

Summary

In wasmtime-wasi, when a filesystem preopen is given DirPerms::all() and FilePerms::READ without FilePerms::WRITE, this wasmtime-wasi enforced access control mechanism can be bypassed by using the wasip2 descriptor.open-at or wasip1 path_open interfaces by opening a file with OpenFlags::TRUNCATE oflag only, for example:

```rust

dir_descriptor.open_at(

PathFlags::empty(),

FILENAME,

OpenFlags::TRUNCATE,

DescriptorFlags::READ,

)

```

```rust

wasip1::path_open(

dir_fd,

0,

FILENAME,

wasip1::OFLAGS_TRUNC,

wasip1::RIGHTS_FD_READ,

0,

0

)

```

The root cause is that the clause that considered OpenFlags::TRUNCATE did not set open_mode |= OpenMode::WRITE;, used later in that function for the access control check against FilePerms for whether opening that file is permitted. With the bug corrected, these calls to open-at and path_open fail with error-code.not-permitted and ERRNO_PERM respectively.

The bug in crates/wasi/src/filesystem.rs, Dir::open_at, lines 967–969:

```rust

if oflags.contains(OpenFlags::TRUNCATE) {

opts.truncate(true).write(true);

}

```

and the single line fix is:

```rust

if oflags.contains(OpenFlags::TRUNCATE) {

opts.truncate(true).write(true);

open_mode |= OpenMode::WRITE;

}

```

Only wasmtime-wasi embeddings that use a combination of DirPerms::MUTATE with FilePerms::READ are affected by this bug, e.g. those that use in the WasiCtxBuilder:

```rust

builder.preopened_dir("readonly", "readonly", DirPerms::READ | DirPerms::MUTATE, FilePerms::READ);

```

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.

How this vulnerability can be exploited

This issue can be reached over the network, attack complexity is low, an attacker needs no privileges on the target. No user interaction is required. The scope is unchanged, so the impact stays within the vulnerable component. Rated impact: confidentiality none, integrity high, availability none.

CVSS metrics in full

The score comes from this vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

  • Attack vector: Network — reachable from anywhere that can route to the service.
  • Attack complexity: Low — the attack works reliably, with no preparation.
  • Privileges required: None — an unauthenticated stranger can try it.
  • User interaction: None — nobody has to be tricked into anything.
  • Scope: Unchanged — the damage stays inside the vulnerable component.
  • Confidentiality impact: None.
  • Integrity impact: High — total loss, or loss the attacker controls.
  • Availability impact: None.

Weakness class

CVE-2026-47261 is classified as CWE-284: Improper Access Control. The software does not restrict an action to the actors that should be allowed to perform it.

Affected software

CVE-2026-47261 is recorded against 2 packages.

  • wasmtime (from 37.0.0 up to 44.0.2)
  • wasmtime-wasi

Timeline and source

Published on 15 June 2026 and last revised on 17 June 2026. No public exploit is currently recorded for this entry. Record sourced from NVD.

References

github.com
github.com
github.com
github.com
github.com

Other advisories for this package

wasmtime has other advisories on record. If you are patching this one, these are worth checking on the same host:

Same weakness in other software

These advisories are the same class of weakness (CWE-284: Improper Access Control) in other software:

Details

Severity HIGH
CVSS Score 8.0
CVSS Vector CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
CWE CWE-284
Public Exploit ✅ No
Source NVD
Published 2026-06-15
Updated 2026-08-20
Modified 2026-06-17
Fix URL N/A

Affected Packages

Software From version Fixed in
wasmtime 37.0.0 44.0.2
wasmtime-wasi — —

Similar Threats

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