bytecodealliance wasmtime up to 24.0.8/36.0.9/44.0.1 FilePerms::READ access control

Summaryinfo

A vulnerability categorized as critical has been discovered in bytecodealliance wasmtime up to 24.0.8/36.0.9/44.0.1. This affects the function FilePerms::READ. The manipulation results in access control. This vulnerability was named CVE-2026-47261. The attack may be performed from remote. There is no available exploit. It is advisable to upgrade the affected component.

Detailsinfo

A vulnerability was found in bytecodealliance wasmtime up to 24.0.8/36.0.9/44.0.1. It has been classified as critical. Affected is the function FilePerms::READ. The manipulation with an unknown input leads to a access control vulnerability. CWE is classifying the issue as CWE-284. The product does not restrict or incorrectly restricts access to a resource from an unauthorized actor. This is going to have an impact on confidentiality, integrity, and availability. CVE summarizes:

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.

The advisory is shared for download at github.com. This vulnerability is traded as CVE-2026-47261 since 05/19/2026. The exploitability is told to be easy. It is possible to launch the attack remotely. The exploitation doesn't require any form of authentication. There are known technical details, but no exploit is available. The MITRE ATT&CK project declares the attack technique as T1068.

Upgrading to version 24.0.9, 36.0.10 or 44.0.2 eliminates this vulnerability. The upgrade is hosted for download at github.com.

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Productinfo

Vendor

• bytecodealliance

Name

• wasmtime

Version

• 24.0.0
• 24.0.1
• 24.0.2
• 24.0.3
• 24.0.4
• 24.0.5
• 24.0.6
• 24.0.7
• 24.0.8
• 36.0.0
• 36.0.1
• 36.0.2
• 36.0.3
• 36.0.4
• 36.0.5
• 36.0.6
• 36.0.7
• 36.0.8
• 36.0.9
• 44.0.0
• 44.0.1

Website

• Product: https://github.com/bytecodealliance/wasmtime/

CPE 2.3info

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