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

What is CVE-2026-47261?

CVE-2026-47261 is a high-severity vulnerability in bytecodealliance wasmtime, published on 15 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

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.

Weakness: CWE-284

Which versions are affected by CVE-2026-47261?

7 open source packages ship an affected version, including wasmtime-wasi. It affects 1 product.

Products include Bytecodealliance Wasmtime.

How do I fix CVE-2026-47261?

Upgrade wasmtime-wasi to a fixed version for your release line: 24.0.9, 36.0.10, 44.0.2 or 45.0.0.

Is CVE-2026-47261 being exploited?

There is no known exploitation of CVE-2026-47261 in the wild and no public exploit code.

Other vulnerabilities in bytecodealliance wasmtime

• CVE-2026-34971 Wasmtime miscompiled guest heap access enables sandbox escape on aarch64 Cranelift Critical 9.0
• CVE-2026-34987 Wasmtime with Winch compiler backend on aarch64 may allow a sandbox-escaping memory access Critical 9.0
• CVE-2022-39393 Wasmtime vulnerable to data leakage between instances in the pooling allocator High 8.6
• CVE-2022-24791 Use after free in Wasmtime High 8.1
• CVE-2026-34941 Wasmtime has a Heap OOB read in component model UTF-16 to latin1+utf16 string transcoding Medium 6.9

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as DEBIAN-CVE-2026-47261, GHSA-2r75-cxrj-cmph, JLSEC-2026-1366, RUSTSEC-2026-0149, UBUNTU-CVE-2026-47261.