bytecodealliance wasmtime up to 36.0.6/42.0.1/44.0.0 return numeric conversion

Summaryinfo

A vulnerability was found in bytecodealliance wasmtime up to 36.0.6/42.0.1/44.0.0. It has been declared as problematic. This vulnerability affects unknown code. Executing a manipulation of the argument return can lead to numeric conversion. This vulnerability is handled as CVE-2026-34945. The attack can be executed remotely. There is not any exploit available. It is recommended to upgrade the affected component.

Detailsinfo

A vulnerability has been found in bytecodealliance wasmtime up to 36.0.6/42.0.1/44.0.0 and classified as problematic. This vulnerability affects some unknown processing. The manipulation of the argument return with an unknown input leads to a numeric conversion vulnerability. The CWE definition for the vulnerability is CWE-681. When converting from one data type to another, such as long to integer, data can be omitted or translated in a way that produces unexpected values. If the resulting values are used in a sensitive context, then dangerous behaviors may occur. As an impact it is known to affect confidentiality. CVE summarizes:

Wasmtime is a runtime for WebAssembly. From 25.0.0 to before 36.0.7, 42.0.2, and 43.0.1, Wasmtime's Winch compiler contains a bug where a 64-bit table, part of the memory64 proposal of WebAssembly, incorrectly translated the table.size instruction. This bug could lead to disclosing data on the host's stack to WebAssembly guests. The host's stack can possibly contain sensitive data related to other host-originating operations which is not intended to be disclosed to guests. This bug specifically arose from a mistake where the return value of table.size was statically typed as a 32-bit integer, as opposed to consulting the table's index type to see how large the returned register could be. When combined with details about Wnich's ABI, such as multi-value returns, this can be combined to read stack data from the host, within a guest. This vulnerability is fixed in 36.0.7, 42.0.2, and 43.0.1.

The advisory is shared for download at github.com. This vulnerability was named CVE-2026-34945 since 03/31/2026. The exploitation appears to be easy. The attack can be initiated remotely. There are known technical details, but no exploit is available.

Upgrading to version 36.0.7, 42.0.2 or 44.0.1 eliminates this vulnerability.

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Productinfo

Vendor

• bytecodealliance

Name

• wasmtime

Version

• 36.0.0
• 36.0.1
• 36.0.2
• 36.0.3
• 36.0.4
• 36.0.5
• 36.0.6
• 42.0.0
• 42.0.1
• 44.0

Website

• Product: https://github.com/bytecodealliance/wasmtime/

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