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GHSA-hc7m-r6v8-hg9q
No affected components available
Impact
Wasmtime's Rust embedder API contains an unsound interaction where a WebAssembly shared linear memory could be viewed as a type which provides safe access to the host (Rust) to the contents of the linear memory. This is not sound for shared linear memories, which could be modified in parallel, and this could lead to a data race in the host.
Wasmtime has a wasmtime::Memory type which represents linear memories in a WebAssembly module. Wasmtime also has wasmtime::SharedMemory, however, which represents shared linear memories introduced in the WebAssembly threads proposal. The API of SharedMemory does not provide accessors which return &[u8] in Rust, for example, as that's not a sound type signature when other threads could be modifying memory. The wasmtime::Memory type, however, does provide this API as it's intended to be used with non-shared memories where static knowledge is available that no concurrent or parallel reads or writes are happening. This means that it's not sound to represent a shared linear memory with wasmtime::Memory and it must instead be represented with wasmtime::SharedMemory.
There were two different, erroneous, methods of creating a wasmtime::Memory which represents a shared memory however:
- The
wasmtime::Memory::newconstructor takes aMemoryTypewhich could beshared. This function did not properly reject shared memory types and require usage ofSharedMemory::newinstead. - Capturing a core dump with WebAssembly would expose all linear memories a
wasmtime::Memory. This means that a core dump would perform an unsynchronized read of shared linear memory, possibly leading to data races.
This is a bug in Wasmtime's safe Rust API. It should not be possible to cause unsoundness with Wasmtime's embedding API if unsafe is not used. Embeddings which do not use the wasm threads proposal nor created shared memories nor actually share shared memories across threads are unaffected. Only if shared memories are created across threads might an embedding be affected.
Patches
Patch releases have been issued for all supported versions of Wasmtime, notably: 24.0.5, 36.0.3, 37.0.3, and 38.0.4. These releases reject creation of shared memories via Memory::new and shared memories are now excluded from core dumps.
Workarounds
Embeddings affected by this issue should use SharedMemory::new instead of Memory::new to create shared memories. Affected embeddings should also disable core dumps if they are unable to upgrade. Note that core dumps are disabled by default but the wasm threads proposal (and shared memory) is enabled by default. It's recommended to upgrade to a patched version of Wasmtime, however.
The vulnerability requires local access to the device to be exploited. It is difficult for an attacker to exploit this vulnerability and may require special conditions. An attacker needs high-level or administrative privileges. The attacker needs the user to perform some action, like clicking a link. The impact is confined to the system where the vulnerability exists. There is a low impact on the integrity of the data.
Limited exploitation activity has been observed. Close monitoring and planned remediation are recommended.
The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.
We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.
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