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CVE-2026-34945— Wasmtime leaks host data with 64-bit tables and Winch

Quick assessment

Affected
bytecodealliance wasmtime
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

wasmtime是Bytecode Alliance开源的一个轻量级WebAssembly运行时。 Wasmtime 25.0.0至36.0.7之前版本、42.0.2之前版本和43.0.1之前版本存在安全漏洞，该漏洞源于Winch编译器错误地翻译了作为WebAssembly memory64提案一部分的64位表的table.size指令，可能导致将主机堆栈上的数据泄露给WebAssembly访客，这些数据可能包含与其他主机操作相关的敏感信息。

AI Predicted 7.5 Difficulty: Moderate EPSS 0.38% · P30

Possible ATT&CK Techniques 1 AI

T1005 · Data from Local System
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I. Basic Information for CVE-2026-34945

Vulnerability Information
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Vulnerability Title
Wasmtime leaks host data with 64-bit tables and Winch
Source: CVE Program / CVE List V5
Vulnerability Description
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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:L/VI:N/VA:N/SC:L/SI:N/SA:N
Source: CVE Program / CVE List V5
Vulnerability Type
数值类型间的不正确转换
Source: CVE Program / CVE List V5
Vulnerability Title
wasmtime 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
wasmtime是Bytecode Alliance开源的一个轻量级WebAssembly运行时。 Wasmtime 25.0.0至36.0.7之前版本、42.0.2之前版本和43.0.1之前版本存在安全漏洞，该漏洞源于Winch编译器错误地翻译了作为WebAssembly memory64提案一部分的64位表的table.size指令，可能导致将主机堆栈上的数据泄露给WebAssembly访客，这些数据可能包含与其他主机操作相关的敏感信息。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
bytecodealliance wasmtime >= 25.0.0, < 36.0.7 -

II. Public POCs for CVE-2026-34945

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III. Intelligence Information for CVE-2026-34945

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Same Patch Batch · bytecodealliance · 2026-04-09 · 12 CVEs total

CVE-2026-35195 Wasmtime has an out-of-bounds write or crash when transcoding component model strings
CVE-2026-35186 Wasmtime has an improperly masked return value from `table.grow` with Winch compiler backe
CVE-2026-34983 Wasmtime has a use-after-free bug after cloning `wasmtime::Linker`
CVE-2026-34941 Wasmtime has a Heap OOB read in component model UTF-16 to latin1+utf16 string transcoding
CVE-2026-34942 Wasmtime panics when transcoding misaligned utf-16 strings
CVE-2026-34988 Wasmtime leaks data between pooling allocator instances
CVE-2026-34971 Wasmtime miscompiled guest heap access enables sandbox escape on aarch64 Cranelift
CVE-2026-34946 Wasmtime's host panics when Winch compiler executes `table.fill`
CVE-2026-34944 Wasmtime segfault or unused out-of-sandbox load with `f64x2.splat` operator on x86-64
CVE-2026-34987 Wasmtime with Winch compiler backend on aarch64 may allow a sandbox-escaping memory access
CVE-2026-34943 Wasmtime panics when lifting `flags` component value

IV. Related Vulnerabilities

Same product: wasmtime
Same vendor: bytecodealliance
Same weakness: CWE-681

V. Comments for CVE-2026-34945

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