Bug 2457004 (CVE-2026-34945)

Summary: CVE-2026-34945 wasmtime: winch: Wasmtime Winch compiler: Information disclosure via incorrect table.size instruction translation
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
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Priority: medium    
Version: unspecifiedKeywords: Security
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OS: Linux   
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A flaw was found in Wasmtime's Winch compiler. This vulnerability, present in versions from 25.0.0 to before 36.0.7, 42.0.2, and 43.0.1, arises from an incorrect translation of the `table.size` instruction for 64-bit WebAssembly tables. An attacker, by crafting a malicious WebAssembly guest, could exploit this flaw to read sensitive data from the host's stack. This information disclosure could expose data related to other host operations that should not be accessible to guests.
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Bug Depends On: 2457173    
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Description OSIDB Bzimport 2026-04-09 19:02:32 UTC 
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.