Impact

Wasmtime's native implementation of WASIp1 suffers from a leak in the fdrenumber function where the file descriptor being renumbered to is not properly closed. Wasmtime's implementation erroneously only updated the table of descriptors for WASIp1 and didn't update the underlying table of descriptors used by the host. This behavior means that while fdrenumber works correctly from a guest's perspective it ends up leaking resources in the host that aren't cleaned up until the corresponding Store is destroyed. This means that guests can, in a loop, use fdrenumber to cause hosts to exhaust resources or exhaust file descriptors.

This bug only affects the native implementation of WASIp1. This means that only runtimes which load core wasm modules and expose fdrenumber are affected. Runtimes are additionally only affected if they expose the ability to acquire a file descriptor, such as opening a file. For runtimes that deny access to files they are unaffected.

Patches

Wasmtime 24.0.10, 36.0.11, 44.0.3, and 45.0.2 have been released which fix this issue.

Workarounds

There are no workarounds for this issue and hosts are recommended to update.