CVE-2026-34987
CVE-2026-34987 · Wasmtime with Winch compiler backend on aarch64 may allow a sandbox-escaping memory access
This page contains facts from public vulnerability sources. Check the original advisory before updating.
Wasmtime is a runtime for WebAssembly. From 25.0.0 to before 36.0.7, 42.0.2, and 43.0.1, Wasmtime with its Winch (baseline) non-default compiler backend may allow properly constructed guest Wasm to access host memory outside of its linear-memory sandbox. This vulnerability requires use of the Winch compiler (-Ccompiler=winch). By default, Wasmtime uses its Cranelift backend, not Winch. With Winch, the same incorrect assumption is present in theory on both aarch64 and x86-64. The aarch64 case has an observed-working proof of concept, while the x86-64 case is theoretical and may not be reachable in practice. This Winch compiler bug can allow the Wasm guest to access memory before or after the linear-memory region, independently of whether pre- or post-guard regions are configured. The accessible range in the initial bug proof-of-concept is up to 32KiB before the start of memory, or ~4GiB after the start of memory, independently of the size of pre- or post-guard regions or the use of explicit or guard-region-based bounds checking. However, the underlying bug assumes a 32-bit memory offset stored in a 64-bit register has its upper bits cleared when it may not, and so closely related variants of the initial proof-of-concept may be able to access truly arbitrary memory in-process. This could result in a host process segmentation fault (DoS), an arbitrary data leak from the host process, or with a write, potentially an arbitrary RCE. This vulnerability is fixed in 36.0.7, 42.0.2, and 43.0.1.
CVSS 9.0 · Critical · EPSS 0.5% · Fix available
- Published
- Updated
Stack: system
Affected products and versions
wasmtime
- Versions
- >= 25.0.0, < 36.0.7: Affected
- >= 37.0.0, < 42.0.2: Affected
- >= 43.0.0, < 44.0.1: Affected
No fix published
rust-wasmtime Debian:13
- Versions
- 26.0.1+dfsg-10
- 26.0.1+dfsg-3
- 26.0.1+dfsg-4
- 26.0.1+dfsg-5
- 26.0.1+dfsg-6
- 26.0.1+dfsg-7
- 26.0.1+dfsg-8
- 26.0.1+dfsg-9
- 27.0.0+dfsg-2
- 27.0.0+dfsg-3
- 27.0.0+dfsg-4
- 28.0.1+dfsg-1
- 28.0.1+dfsg-2
- 28.0.1+dfsg-3
- 29.0.1+dfsg-1
- 29.0.1+dfsg-2
- 29.0.1+dfsg-3
- 29.0.1+dfsg-4
- 29.0.1+dfsg-5
- 29.0.1+dfsg-6
- 29.0.1+dfsg-7
- 29.0.1+dfsg-8
- 36.0.11+dfsg-1
- 36.0.12+dfsg-1
- 36.0.12+dfsg-2
- 36.0.12+dfsg-3
- 36.0.13+dfsg-1
- 36.0.5+dfsg-1
- 36.0.5+dfsg-2
- 36.0.5+dfsg-3
- 36.0.5+dfsg-4
- 36.0.5+dfsg-5
- 36.0.6+dfsg-1
- 36.0.6+dfsg-2
- 36.0.6+dfsg-3
- 36.0.6+dfsg-4
- 36.0.6+dfsg-5
- 36.0.6+dfsg-6
- 36.0.6+dfsg-7
- 36.0.7+dfsg-1
- 36.0.8+dfsg-1
- 36.0.9+dfsg-1
- 36.0.9+dfsg-2
- Affected ranges
- ECOSYSTEM: (−∞, +∞)
No fix published
rust-wasmtime Debian:14
- Versions
- 26.0.1+dfsg-10
- 26.0.1+dfsg-3
- 26.0.1+dfsg-4
- 26.0.1+dfsg-5
- 26.0.1+dfsg-6
- 26.0.1+dfsg-7
- 26.0.1+dfsg-8
- 26.0.1+dfsg-9
- 27.0.0+dfsg-2
- 27.0.0+dfsg-3
- 27.0.0+dfsg-4
- 28.0.1+dfsg-1
- 28.0.1+dfsg-2
- 28.0.1+dfsg-3
- 29.0.1+dfsg-1
- 29.0.1+dfsg-2
- 29.0.1+dfsg-3
- 29.0.1+dfsg-4
- 29.0.1+dfsg-5
- 29.0.1+dfsg-6
- 29.0.1+dfsg-7
- 29.0.1+dfsg-8
- 36.0.5+dfsg-1
- 36.0.5+dfsg-2
- 36.0.5+dfsg-3
- 36.0.5+dfsg-4
- 36.0.5+dfsg-5
- 36.0.6+dfsg-1
- 36.0.6+dfsg-2
- 36.0.6+dfsg-3
- 36.0.6+dfsg-4
- 36.0.6+dfsg-5
- 36.0.6+dfsg-6
- 36.0.6+dfsg-7
- Affected ranges
- ECOSYSTEM: < 36.0.7+dfsg-1
Update to 36.0.7+dfsg-1
rust-wasmtime Ubuntu:24.04:LTS
- Versions
- 10.0.1+dfsg-7
- 15.0.1+dfsg-4
- 16.0.0+dfsg-2
- 16.0.0+dfsg-3
- Affected ranges
- ECOSYSTEM: (−∞, +∞)
No fix published
rust-wasmtime Ubuntu:25.10
- Versions
- 26.0.1+dfsg-3
- Affected ranges
- ECOSYSTEM: (−∞, +∞)
No fix published
rust-wasmtime Ubuntu:26.10
- Versions
- 36.0.5+dfsg-1
- 36.0.13+dfsg-1
- Affected ranges
- ECOSYSTEM: (−∞, +∞)
No fix published
rust-wasmtime Ubuntu:26.04:LTS
- Versions
- 26.0.1+dfsg-3
- 26.0.1+dfsg-4
- 28.0.1+dfsg-3
- 29.0.1+dfsg-5
- 36.0.5+dfsg-1
- Affected ranges
- ECOSYSTEM: (−∞, +∞)
No fix published