CVE-2026-35186 (GCVE-0-2026-35186)

Vulnerability from cvelistv5 – Published: 2026-04-09 18:54 – Updated: 2026-04-09 18:54
VLAI?
Title
Wasmtime has an improperly masked return value from `table.grow` with Winch compiler backend
Summary
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 backend contains a bug where translating the table.grow operator causes the result to be incorrectly typed. For 32-bit tables this means that the result of the operator, internally in Winch, is tagged as a 64-bit value instead of a 32-bit value. This invalid internal representation of Winch's compiler state compounds into further issues depending on how the value is consumed. The primary consequence of this bug is that bytes in the host's address space can be stored/read from. This is only applicable to the 16 bytes before linear memory, however, as the only significant return value of table.grow that can be misinterpreted is -1. The bytes before linear memory are, by default, unmapped memory. Wasmtime will detect this fault and abort the process, however, because wasm should not be able to access these bytes. Overall this this bug in Winch represents a DoS vector by crashing the host process, a correctness issue within Winch, and a possible leak of up to 16-bytes before linear memory. Wasmtime's default compiler is Cranelift, not Winch, and Wasmtime's default settings are to place guard pages before linear memory. This means that Wasmtime's default configuration is not affected by this issue, and when explicitly choosing Winch Wasmtime's otherwise default configuration leads to a DoS. Disabling guard pages before linear memory is required to possibly leak up to 16-bytes of host data. This vulnerability is fixed in 36.0.7, 42.0.2, and 43.0.1.
CWE
  • CWE-789 - Memory Allocation with Excessive Size Value
Assigner
References
Impacted products
Vendor Product Version
bytecodealliance wasmtime Affected: >= 25.0.0, < 36.0.7
Affected: >= 37.0.0, < 42.0.2
Affected: >= 43.0.0, < 44.0.1
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{
  "containers": {
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      "affected": [
        {
          "product": "wasmtime",
          "vendor": "bytecodealliance",
          "versions": [
            {
              "status": "affected",
              "version": "\u003e= 25.0.0, \u003c 36.0.7"
            },
            {
              "status": "affected",
              "version": "\u003e= 37.0.0, \u003c 42.0.2"
            },
            {
              "status": "affected",
              "version": "\u003e= 43.0.0, \u003c 44.0.1"
            }
          ]
        }
      ],
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          "value": "Wasmtime is a runtime for WebAssembly. From 25.0.0 to before 36.0.7, 42.0.2, and 43.0.1, Wasmtime\u0027s Winch compiler backend contains a bug where translating the table.grow operator causes the result to be incorrectly typed. For 32-bit tables this means that the result of the operator, internally in Winch, is tagged as a 64-bit value instead of a 32-bit value. This invalid internal representation of Winch\u0027s compiler state compounds into further issues depending on how the value is consumed. The primary consequence of this bug is that bytes in the host\u0027s address space can be stored/read from. This is only applicable to the 16 bytes before linear memory, however, as the only significant return value of table.grow that can be misinterpreted is -1. The bytes before linear memory are, by default, unmapped memory. Wasmtime will detect this fault and abort the process, however, because wasm should not be able to access these bytes. Overall this this bug in Winch represents a DoS vector by crashing the host process, a correctness issue within Winch, and a possible leak of up to 16-bytes before linear memory. Wasmtime\u0027s default compiler is Cranelift, not Winch, and Wasmtime\u0027s default settings are to place guard pages before linear memory. This means that Wasmtime\u0027s default configuration is not affected by this issue, and when explicitly choosing Winch Wasmtime\u0027s otherwise default configuration leads to a DoS. Disabling guard pages before linear memory is required to possibly leak up to 16-bytes of host data. This vulnerability is fixed in 36.0.7, 42.0.2, and 43.0.1."
        }
      ],
      "metrics": [
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            "attackComplexity": "HIGH",
            "attackRequirements": "PRESENT",
            "attackVector": "NETWORK",
            "baseScore": 6.1,
            "baseSeverity": "MEDIUM",
            "privilegesRequired": "LOW",
            "subAvailabilityImpact": "NONE",
            "subConfidentialityImpact": "NONE",
            "subIntegrityImpact": "NONE",
            "userInteraction": "NONE",
            "vectorString": "CVSS:4.0/AV:N/AC:H/AT:P/PR:L/UI:N/VC:L/VI:L/VA:H/SC:N/SI:N/SA:N",
            "version": "4.0",
            "vulnAvailabilityImpact": "HIGH",
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        "dateUpdated": "2026-04-09T18:54:48.760Z",
        "orgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
        "shortName": "GitHub_M"
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          "tags": [
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          "url": "https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-f984-pcp8-v2p7"
        }
      ],
      "source": {
        "advisory": "GHSA-f984-pcp8-v2p7",
        "discovery": "UNKNOWN"
      },
      "title": "Wasmtime has an improperly masked return value from `table.grow` with Winch compiler backend"
    }
  },
  "cveMetadata": {
    "assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
    "assignerShortName": "GitHub_M",
    "cveId": "CVE-2026-35186",
    "datePublished": "2026-04-09T18:54:48.760Z",
    "dateReserved": "2026-04-01T17:26:21.134Z",
    "dateUpdated": "2026-04-09T18:54:48.760Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
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  }
}


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Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
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