Wasmtime is a runtime for WebAssembly. From 46.0.0 until 46.0.2 and 47.0.3, fuel and epoch preemption checks inside bulk operations including memory.copy, table.grow, and array.copy can expose invalid intermediate state when an embedder mutates a Store in Store::epoch_deadline_callback or continues using a Store after cancellation or a trap. A cancelled non-nullable table growth can leave null elements, linear-memory growth during memory.copy can invalidate retained raw pointers, and callback-triggered garbage collection during array.copy can invalidate GC pointers, resulting in a crash, invalid memory access, or GC heap corruption. Embeddings whose callbacks only access the host data in Store, and embeddings that discard a Store after timeout or epoch deadline, are not affected. This issue is fixed in versions 46.0.2 and 47.0.3.
Weakness
The product contains a concurrent code sequence that requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence operating concurrently.
Extended Description
A race condition occurs within concurrent environments, and it is effectively a property of a code sequence. Depending on the context, a code sequence may be in the form of a function call, a small number of instructions, a series of program invocations, etc. A race condition violates these properties, which are closely related:
A race condition exists when an “interfering code sequence” can still access the shared resource, violating exclusivity. The interfering code sequence could be “trusted” or “untrusted.” A trusted interfering code sequence occurs within the product; it cannot be modified by the attacker, and it can only be invoked indirectly. An untrusted interfering code sequence can be authored directly by the attacker, and typically it is external to the vulnerable product.
Potential Mitigations
- Minimize the usage of shared resources in order to remove as much complexity as possible from the control flow and to reduce the likelihood of unexpected conditions occurring.
- Additionally, this will minimize the amount of synchronization necessary and may even help to reduce the likelihood of a denial of service where an attacker may be able to repeatedly trigger a critical section (CWE-400).
Related Attack Patterns
References
- https://github.com/bytecodealliance/wasmtime/commit/3ebfbe5af4927c157d6fcaca42b8dbb6d17b73fb
- https://github.com/bytecodealliance/wasmtime/commit/99b0bc39d447317a4102c056081c83a9a84a46e0
- https://github.com/bytecodealliance/wasmtime/commit/a3eb27af01ba5a30320a90ea1405059cdfedd353
- https://github.com/bytecodealliance/wasmtime/pull/14041
- https://github.com/bytecodealliance/wasmtime/pull/14043
- https://github.com/bytecodealliance/wasmtime/pull/14045
- https://github.com/bytecodealliance/wasmtime/releases/tag/v46.0.2
- https://github.com/bytecodealliance/wasmtime/releases/tag/v47.0.3
- https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-2hw9-mc66-jc2q