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

Quick assessment

Affected
bytecodealliance wasmtime
Exploitation
Public or AI PoC available; prioritize validation
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

bytecodealliance Wasmtime是bytecodealliance组织开源的一个WebAssembly与WASI运行时。 Bytecode Alliance wasmtime 24.0.9之前版本、36.0.10之前版本和44.0.2之前版本存在权限许可和访问控制问题漏洞，该漏洞源于访问控制机制可被绕过，当文件系统预打开指定DirPerms::all()和FilePerms::READ而没有FilePerms::WRITE时，通过wasip2 descriptor.open-at或was

CVSS 7.5 · High EPSS 0.50% · P41

Affected Version Matrix 3

VendorProduct Version RangeStatus
bytecodealliance wasmtime >= 37.0.0, < 44.0.2 affected
>= 25.0.0, < 36.0.10 affected
< 24.0.9 affected
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I. Basic Information for CVE-2026-47261

Vulnerability Information
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Vulnerability Title
Wasmtime: WASI path_open(TRUNCATE) bypasses `FilePerms::WRITE` host restriction
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
访问控制不恰当
Source: CVE Program / CVE List V5
Vulnerability Title
Bytecode Alliance wasmtime 权限许可和访问控制问题漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
bytecodealliance Wasmtime是bytecodealliance组织开源的一个WebAssembly与WASI运行时。 Bytecode Alliance wasmtime 24.0.9之前版本、36.0.10之前版本和44.0.2之前版本存在权限许可和访问控制问题漏洞，该漏洞源于访问控制机制可被绕过，当文件系统预打开指定DirPerms::all()和FilePerms::READ而没有FilePerms::WRITE时，通过wasip2 descriptor.open-at或was
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
bytecodealliance wasmtime >= 37.0.0, < 44.0.2 -

II. Public POCs for CVE-2026-47261

# POC Description Source Link Shenlong Link
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Qwen3.6-35B-A3B · 11377 chars
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III. Intelligence Information for CVE-2026-47261

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Vendor Advisories for CVE-2026-47261 (1)

Vendor Pages for CVE-2026-47261 (3)

Other References for CVE-2026-47261 (1)

IV. Related Vulnerabilities

Same product: wasmtime
Same vendor: bytecodealliance
Same weakness: CWE-284

V. Comments for CVE-2026-47261

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