{
  "cveId": "CVE-2026-34987",
  "url": "https://patchblox.com/security/cve/CVE-2026-34987",
  "summary": "CVE-2026-34987 is fixed in rust-wasmtime on 1 platform by DEBIAN-CVE-2026-34987 (version 36.0.7\u002Bdfsg-1), released April 9, 2026. It is not reported as exploited. Patch Radar priority: Urgent.",
  "title": "rust-wasmtime: Wasmtime is a runtime for WebAssembly",
  "description": "Wasmtime is a runtime for WebAssembly. From 25.0.0 to before 36.0.7, 42.0.2, and 43.0.1, Wasmtime with its Winch (baseline) non-default compiler backend may allow properly constructed guest Wasm to access host memory outside of its linear-memory sandbox. This vulnerability requires use of the Winch compiler (-Ccompiler=winch). By default, Wasmtime uses its Cranelift backend, not Winch. With Winch, the same incorrect assumption is present in theory on both aarch64 and x86-64. The aarch64 case has an observed-working proof of concept, while the x86-64 case is theoretical and may not be reachable in practice. This Winch compiler bug can allow the Wasm guest to access memory before or after the linear-memory region, independently of whether pre- or post-guard regions are configured. The accessible range in the initial bug proof-of-concept is up to 32KiB before the start of memory, or ~4GiB after the start of memory, independently of the size of pre- or post-guard regions or the use of explicit or guard-region-based bounds checking. However, the underlying bug assumes a 32-bit memory offset stored in a 64-bit register has its upper bits cleared when it may not, and so closely related variants of the initial proof-of-concept may be able to access truly arbitrary memory in-process. This could result in a host process segmentation fault (DoS), an arbitrary data leak from the host process, or with a write, potentially an arbitrary RCE. This vulnerability is fixed in 36.0.7, 42.0.2, and 43.0.1.",
  "published": "2026-04-09T19:16:25Z",
  "severity": "critical",
  "cvss": 9.9,
  "cvssVector": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H",
  "epss": 0.00283,
  "epssPercentile": 0.20964,
  "priority": "Urgent",
  "priorityTier": 2,
  "exploited": false,
  "vendorExploited": false,
  "disclosed": false,
  "fixes": [
    {
      "platform": "linux",
      "product": "rust-wasmtime",
      "release": "Debian 14",
      "fixedVersion": "36.0.7\u002Bdfsg-1",
      "fix": "DEBIAN-CVE-2026-34987",
      "url": "https://patchblox.com/security/fix/linux/debian-cve-2026-34987",
      "released": "2026-04-09T19:16:25Z"
    }
  ],
  "noFixYet": [],
  "dataAsOf": "2026-11-08T13:06:02Z",
  "attribution": {
    "text": "Data: Patchblox Patch Radar",
    "url": "https://patchblox.com/security/patch-radar",
    "terms": "https://patchblox.com/security/patch-radar/use-the-data"
  }
}