Vulnerability · Published Jun 15, 2026 · Assigned by GitHub_M
CVE-2026-47261Wasmtime: WASI path_open(TRUNCATE) bypasses `FilePerms::WRITE` host restriction
High 7.5
In plain English
A high-severity improper access control in wasmtime from bytecodealliance. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 30% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:13 | rust-wasmtime | no fix listed | DEBIAN-CVE-2026-47261 |
| Debian:14 | rust-wasmtime | 36.0.11+dfsg-1 | DEBIAN-CVE-2026-47261 |
| Ubuntu:24.04:LTS | rust-wasmtime | no fix listed | UBUNTU-CVE-2026-47261 |
| Ubuntu:25.10 | rust-wasmtime | no fix listed | UBUNTU-CVE-2026-47261 |
| Ubuntu:26.04:LTS | rust-wasmtime | no fix listed | UBUNTU-CVE-2026-47261 |
| Ubuntu:26.10 | rust-wasmtime | no fix listed | UBUNTU-CVE-2026-47261 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| bytecodealliance | wasmtime | >= 37.0.0, < 44.0.2>= 25.0.0, < 36.0.10< 24.0.9 |
Weakness: CWE-284 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
References
- https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-2r75-cxrj-cmph x_refsource_CONFIRM
- https://github.com/bytecodealliance/wasmtime/releases/tag/v24.0.9 x_refsource_MISC
- https://github.com/bytecodealliance/wasmtime/releases/tag/v36.0.10 x_refsource_MISC
- https://github.com/bytecodealliance/wasmtime/releases/tag/v44.0.2 x_refsource_MISC
- https://github.com/bytecodealliance/wasmtime/releases/tag/v45.0.0 x_refsource_MISC