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CVE-2026-34942— Wasmtime panics when transcoding misaligned utf-16 strings

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 24.0.7之前版本、36.0.7之前版本、42.0.2之前版本和43.0.1之前版本存在输入验证错误漏洞，该漏洞源于将字符串转码到组件模型的utf16或latin1+utf16编码时，未正确验证重新分配字符串的对齐方式，可能导致传递未对齐指针给主机进行转码，从而触发主机恐慌，构成拒绝服务向量。

AI Predicted 5.9 Difficulty: Moderate EPSS 0.35% · P28
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I. Basic Information for CVE-2026-34942

Vulnerability Information
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Vulnerability Title
Wasmtime panics when transcoding misaligned utf-16 strings
Source: CVE Program / CVE List V5
Vulnerability Description
Wasmtime is a runtime for WebAssembly. Prior to 24.0.7, 36.0.7, 42.0.2, and 43.0.1, Wasmtime's implementation of transcoding strings into the Component Model's utf16 or latin1+utf16 encodings improperly verified the alignment of reallocated strings. This meant that unaligned pointers could be passed to the host for transcoding which would trigger a host panic. This panic is possible to trigger from malicious guests which transfer very specific strings across components with specific addresses. Host panics are considered a DoS vector in Wasmtime as the panic conditions are controlled by the guest in this situation. This vulnerability is fixed in 24.0.7, 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:L
Source: CVE Program / CVE List V5
Vulnerability Type
对数组索引的验证不恰当
Source: CVE Program / CVE List V5
Vulnerability Title
wasmtime 输入验证错误漏洞
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 24.0.7之前版本、36.0.7之前版本、42.0.2之前版本和43.0.1之前版本存在输入验证错误漏洞，该漏洞源于将字符串转码到组件模型的utf16或latin1+utf16编码时，未正确验证重新分配字符串的对齐方式，可能导致传递未对齐指针给主机进行转码，从而触发主机恐慌，构成拒绝服务向量。
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 < 24.0.7 -

II. Public POCs for CVE-2026-34942

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III. Intelligence Information for CVE-2026-34942

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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-2026-34988 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-2026-34945 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-129

V. Comments for CVE-2026-34942

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