Wasmtime: WASI path_open(TRUNCATE) bypasses `FilePerms::WRITE` host restriction

Summary

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.

Timeline

1. Jun 15, 2026, 7:47 PM UTCCVE published
2. Jun 16, 2026, 12:45 PM UTCCISA SSVC assessment

   Exploitation: none · Automatable: yes · Technical impact: partial

3. Jun 16, 2026, 12:46 PM UTCRecord last updated

Affected versions

• bytecodealliance wasmtime

  From 37.0.0 · fixed in 44.0.2; From 25.0.0 · fixed in 36.0.10; fixed in 24.0.9

• wasmtime-wasicrates.io

  From 37.0.0 · fixed in 44.0.2

• wasmtime-wasicrates.io

  From 25.0.0 · fixed in 36.0.10

• wasmtime-wasicrates.io

  fixed in 24.0.9

• wasmtime-wasicrates.io

  From 0.0.0-0 · fixed in 24.0.9; From 25.0.0 · fixed in 36.0.10; From 37.0.0 · fixed in 44.0.2; From 45.0.0 · fixed in 45.0.0

References 5