Wasmtime: WASI path_open(TRUNCATE) bypasses `FilePerms::WRITE` host restriction_CVE-2026-47261

7.5 / 10

HIGH

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

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.

Basic Information

ID CVE-2026-47261

Source GitHub_M

Published Jun 15, 2026 at 19:47

Affected Product

Vendor bytecodealliance

Product wasmtime

Version >= 37.0.0, < 44.0.2

Affected Versions bytecodealliance wasmtime >= 37.0.0, < 44.0.2
bytecodealliance wasmtime >= 25.0.0, < 36.0.10
bytecodealliance wasmtime < 24.0.9

CWE Classification

CWE-284

References

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    "lastseen": "",
    "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\u2013969) 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.",
    "published": "2026-06-15T19:47:40.366Z",
    "modified": "2026-06-15T19:47:40.366Z",
    "type": "cve",
    "title": "Wasmtime: WASI path_open(TRUNCATE) bypasses `FilePerms::WRITE` host restriction",
    "source": "GitHub_M",
    "references": "https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-2r75-cxrj-cmph\nhttps://github.com/bytecodealliance/wasmtime/releases/tag/v24.0.9\nhttps://github.com/bytecodealliance/wasmtime/releases/tag/v36.0.10\nhttps://github.com/bytecodealliance/wasmtime/releases/tag/v44.0.2\nhttps://github.com/bytecodealliance/wasmtime/releases/tag/v45.0.0",
    "id": "CVE-2026-47261",
    "bulletinFamily": "",
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    "sourceData": "bytecodealliance wasmtime >= 37.0.0, < 44.0.2\nbytecodealliance wasmtime >= 25.0.0, < 36.0.10\nbytecodealliance wasmtime < 24.0.9",
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    "product": "wasmtime",
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