{
  "affected": [
    {
      "ranges": [
        {
          "database_specific": {
            "cpe": [
              "cpe:2.3:a:bytecodealliance:wasmtime:*:*:*:*:*:rust:*:*",
              "cpe:2.3:a:bytecodealliance:wasmtime:43.0.0:*:*:*:*:rust:*:*"
            ],
            "extracted_events": [
              {
                "introduced": "25.0.0"
              },
              {
                "fixed": "36.0.7"
              },
              {
                "introduced": "37.0.0"
              },
              {
                "fixed": "42.0.2"
              },
              {
                "introduced": "43.0.0"
              },
              {
                "last_affected": "43.0.0"
              }
            ],
            "source": [
              "CPE_RANGE",
              "CPE_STRING"
            ]
          },
          "events": [
            {
              "introduced": "0b195ef5db76c02fb5392ec1418c58bdc5537d41"
            },
            {
              "fixed": "09539085b9b514b65d5c51e2905dc38f6eb414b9"
            },
            {
              "introduced": "7b3d6ae79e9153a2477668062f5622c10333925f"
            },
            {
              "fixed": "403f9929d4e13ed87c76471d4f4bc8d381c876eb"
            },
            {
              "introduced": "be23469ece57c0be64904f12111c8d808b0ce4ac"
            },
            {
              "last_affected": "be23469ece57c0be64904f12111c8d808b0ce4ac"
            }
          ],
          "repo": "https://github.com/bytecodealliance/wasmtime",
          "type": "GIT"
        }
      ],
      "versions": [
        "43.0.0"
      ]
    }
  ],
  "aliases": [
    "GHSA-xx5w-cvp6-jv83"
  ],
  "database_specific": {
    "cna_assigner": "GitHub_M",
    "cwe_ids": [
      "CWE-125",
      "CWE-787"
    ],
    "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/34xxx/CVE-2026-34987.json"
  },
  "details": "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.",
  "id": "CVE-2026-34987",
  "modified": "2026-07-15T01:49:01.094326058Z",
  "published": "2026-04-09T18:48:33.552Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/34xxx/CVE-2026-34987.json"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-xx5w-cvp6-jv83"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-34987"
    }
  ],
  "schema_version": "1.8.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H",
      "type": "CVSS_V4"
    }
  ],
  "summary": "Wasmtime with Winch compiler backend on aarch64 may allow a sandbox-escaping memory access"
}