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CVE-2026-34946— Wasmtime's host panics when Winch compiler executes `table.fill`

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，该漏洞源于编译table.fill指令可能导致主机恐慌，构成拒绝服务漏洞，具体问题源于历史重构更改了编译代码在table.*指令中引用表的方式，但未更新相关的Winch代码路径，导致Winch使用了错误的索引方案。

AI Predicted 7.5 Difficulty: Moderate EPSS 0.42% · P34
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I. Basic Information for CVE-2026-34946

Vulnerability Information
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Vulnerability Title
Wasmtime's host panics when Winch compiler executes `table.fill`
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 vulnerability where the compilation of the table.fill instruction can result in a host panic. This means that a valid guest can be compiled with Winch, on any architecture, and cause the host to panic. This represents a denial-of-service vulnerability in Wasmtime due to guests being able to trigger a panic. The specific issue is that a historical refactoring changed how compiled code referenced tables within the table.* instructions. This refactoring forgot to update the Winch code paths associated as well, meaning that Winch was using the wrong indexing scheme. Due to the feature support of Winch the only problem that can result is tables being mixed up or nonexistent tables being used, meaning that the guest is limited to panicking the host (using a nonexistent table), or executing spec-incorrect behavior and modifying the wrong table. 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:P/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
Source: CVE Program / CVE List V5
Vulnerability Type
控制流实现总是不正确
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，该漏洞源于编译table.fill指令可能导致主机恐慌，构成拒绝服务漏洞，具体问题源于历史重构更改了编译代码在table.*指令中引用表的方式，但未更新相关的Winch代码路径，导致Winch使用了错误的索引方案。
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-2026-34946

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III. Intelligence Information for CVE-2026-34946

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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-2026-34944 Wasmtime segfault or unused out-of-sandbox load with `f64x2.splat` operator on x86-64
CVE-2026-34945 Wasmtime leaks host data with 64-bit tables and Winch
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-670

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