FKIE_CVE-2026-34971

Vulnerability from fkie_nvd - Published: 2026-04-09 19:16 - Updated: 2026-10-26 22:10
Severity
7.8 (High) - CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H
8.5 (High) - CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H
Summary
Wasmtime is a runtime for WebAssembly. From 32.0.0 to before 36.0.7, 42.0.2, and 43.0.1, Wasmtime's Cranelift compilation backend contains a bug on aarch64 when performing a certain shape of heap accesses which means that the wrong address is accessed. When combined with explicit bounds checks a guest WebAssembly module this can create a situation where there are two diverging computations for the same address: one for the address to bounds-check and one for the address to load. This difference in address being operated on means that a guest module can pass a bounds check but then load a different address. Combined together this enables an arbitrary read/write primitive for guest WebAssembly when accesssing host memory. This is a sandbox escape as guests are able to read/write arbitrary host memory. This vulnerability has a few ingredients, all of which must be met, for this situation to occur and bypass the sandbox restrictions. This miscompiled shape of load only occurs on 64-bit WebAssembly linear memories, or when Config::wasm_memory64 is enabled. 32-bit WebAssembly is not affected. Spectre mitigations or signals-based-traps must be disabled. When spectre mitigations are enabled then the offending shape of load is not generated. When signals-based-traps are disabled then spectre mitigations are also automatically disabled. The specific bug in Cranelift is a miscompile of a load of the shape load(iadd(base, ishl(index, amt))) where amt is a constant. The amt value is masked incorrectly to test if it's a certain value, and this incorrect mask means that Cranelift can pattern-match this lowering rule during instruction selection erroneously, diverging from WebAssembly's and Cranelift's semantics. This incorrect lowering would, for example, load an address much further away than intended as the correct address's computation would have wrapped around to a smaller value insetad. This vulnerability is fixed in 36.0.7, 42.0.2, and 43.0.1.
References
security-advisories@github.comhttps://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-jhxm-h53p-jm7wMitigation, Vendor Advisory
0b0ca135-0b70-47e7-9f44-1890c2a1c46chttps://access.redhat.com/security/cve/CVE-2026-34971
0b0ca135-0b70-47e7-9f44-1890c2a1c46chttps://bugzilla.redhat.com/show_bug.cgi?id=2457008
0b0ca135-0b70-47e7-9f44-1890c2a1c46chttps://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-34971.json
Impacted products
Vendor Product Version
bytecodealliance wasmtime *
bytecodealliance wasmtime *
bytecodealliance wasmtime 43.0.0
To clipboard 

{
  "affected": [
    {
      "affectedData": [
        {
          "product": "wasmtime",
          "vendor": "bytecodealliance",
          "versions": [
            {
              "status": "affected",
              "version": "\u003e= 32.0.0, \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"
            }
          ]
        }
      ],
      "source": "security-advisories@github.com"
    },
    {
      "affectedData": [
        {
          "collectionURL": "https://access.redhat.com/downloads/content/package-browser/",
          "cpes": [
            "cpe:/a:redhat:connectivity_link:1"
          ],
          "defaultStatus": "affected",
          "packageName": "redhat-user-workloads/rhcl-1-3-wasm-shim",
          "product": "Red Hat Connectivity Link 1",
          "vendor": "Red Hat"
        },
        {
          "collectionURL": "https://access.redhat.com/downloads/content/package-browser/",
          "cpes": [
            "cpe:/o:redhat:enterprise_linux:10"
          ],
          "defaultStatus": "unaffected",
          "packageName": "virt-firmware-rs",
          "product": "Red Hat Enterprise Linux 10",
          "vendor": "Red Hat"
        }
      ],
      "source": "0b0ca135-0b70-47e7-9f44-1890c2a1c46c"
    }
  ],
  "configurations": [
    {
      "nodes": [
        {
          "cpeMatch": [
            {
              "criteria": "cpe:2.3:a:bytecodealliance:wasmtime:*:*:*:*:*:rust:*:*",
              "matchCriteriaId": "8CDCBF94-C913-4A35-BF9A-B55B4422C9A2",
              "versionEndExcluding": "36.0.7",
              "versionStartIncluding": "32.0.0",
              "vulnerable": true
            },
            {
              "criteria": "cpe:2.3:a:bytecodealliance:wasmtime:*:*:*:*:*:rust:*:*",
              "matchCriteriaId": "1D7B70EB-93E3-4732-AB70-E6A531178941",
              "versionEndExcluding": "42.0.2",
              "versionStartIncluding": "37.0.0",
              "vulnerable": true
            },
            {
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              "matchCriteriaId": "9AD0150A-FE79-4EA6-995B-8CAFC7F246B5",
              "vulnerable": true
            }
          ],
          "negate": false,
          "operator": "OR"
        }
      ]
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "Wasmtime is a runtime for WebAssembly. From 32.0.0 to before 36.0.7, 42.0.2, and 43.0.1, Wasmtime\u0027s Cranelift compilation backend contains a bug on aarch64 when performing a certain shape of heap accesses which means that the wrong address is accessed. When combined with explicit bounds checks a guest WebAssembly module this can create a situation where there are two diverging computations for the same address: one for the address to bounds-check and one for the address to load. This difference in address being operated on means that a guest module can pass a bounds check but then load a different address. Combined together this enables an arbitrary read/write primitive for guest WebAssembly when accesssing host memory. This is a sandbox escape as guests are able to read/write arbitrary host memory. This vulnerability has a few ingredients, all of which must be met, for this situation to occur and bypass the sandbox restrictions. This miscompiled shape of load only occurs on 64-bit WebAssembly linear memories, or when Config::wasm_memory64 is enabled. 32-bit WebAssembly is not affected. Spectre mitigations or signals-based-traps must be disabled. When spectre mitigations are enabled then the offending shape of load is not generated. When signals-based-traps are disabled then spectre mitigations are also automatically disabled. The specific bug in Cranelift is a miscompile of a load of the shape load(iadd(base, ishl(index, amt))) where amt is a constant. The amt value is masked incorrectly to test if it\u0027s a certain value, and this incorrect mask means that Cranelift can pattern-match this lowering rule during instruction selection erroneously, diverging from WebAssembly\u0027s and Cranelift\u0027s semantics. This incorrect lowering would, for example, load an address much further away than intended as the correct address\u0027s computation would have wrapped around to a smaller value insetad. This vulnerability is fixed in 36.0.7, 42.0.2, and 43.0.1."
    },
    {
      "lang": "es",
      "value": "Wasmtime es un entorno de ejecuci\u00f3n para WebAssembly. Desde la versi\u00f3n 32.0.0 hasta antes de las versiones 36.0.7, 42.0.2 y 43.0.1, el backend de compilaci\u00f3n Cranelift de Wasmtime contiene un error en aarch64 al realizar un cierto tipo de accesos a la pila (heap), lo que significa que se accede a la direcci\u00f3n incorrecta. Cuando se combina con comprobaciones de l\u00edmites expl\u00edcitas en un m\u00f3dulo WebAssembly invitado, esto puede crear una situaci\u00f3n en la que hay dos c\u00e1lculos divergentes para la misma direcci\u00f3n: uno para la direcci\u00f3n a comprobar l\u00edmites y otro para la direcci\u00f3n a cargar. Esta diferencia en la direcci\u00f3n sobre la que se opera significa que un m\u00f3dulo invitado puede pasar una comprobaci\u00f3n de l\u00edmites pero luego cargar una direcci\u00f3n diferente. Combinado, esto habilita una primitiva de lectura/escritura arbitraria para WebAssembly invitado al acceder a la memoria del host. Esto es un escape de sandbox ya que los invitados pueden leer/escribir memoria arbitraria del host. Esta vulnerabilidad tiene varios ingredientes, todos los cuales deben cumplirse, para que esta situaci\u00f3n ocurra y se eviten las restricciones del sandbox. Esta forma de carga mal compilada solo ocurre en memorias lineales de WebAssembly de 64 bits, o cuando Config::wasm_memory64 est\u00e1 habilitado. WebAssembly de 32 bits no se ve afectado. Las mitigaciones de Spectre o las trampas basadas en se\u00f1ales deben estar deshabilitadas. Cuando las mitigaciones de Spectre est\u00e1n habilitadas, la forma de carga ofensiva no se genera. Cuando las trampas basadas en se\u00f1ales est\u00e1n deshabilitadas, las mitigaciones de Spectre tambi\u00e9n se deshabilitan autom\u00e1ticamente. El error espec\u00edfico en Cranelift es una compilaci\u00f3n incorrecta de una carga con la forma load(iadd(base, ishl(index, amt))) donde amt es una constante. El valor de amt se enmascara incorrectamente para probar si es un cierto valor, y esta m\u00e1scara incorrecta significa que Cranelift puede hacer coincidir err\u00f3neamente esta regla de reducci\u00f3n (lowering rule) durante la selecci\u00f3n de instrucciones, divergiendo de la sem\u00e1ntica de WebAssembly y Cranelift. Esta reducci\u00f3n incorrecta, por ejemplo, cargar\u00eda una direcci\u00f3n mucho m\u00e1s lejana de lo previsto, ya que el c\u00e1lculo de la direcci\u00f3n correcta habr\u00eda envuelto a un valor menor en su lugar. Esta vulnerabilidad se corrige en las versiones 36.0.7, 42.0.2 y 43.0.1."
    }
  ],
  "id": "CVE-2026-34971",
  "lastModified": "2026-10-26T22:10:00.163",
  "metrics": {
    "cvssMetricV31": [
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        "cvssData": {
          "attackComplexity": "HIGH",
          "attackVector": "LOCAL",
          "availabilityImpact": "HIGH",
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          "confidentialityImpact": "HIGH",
          "integrityImpact": "HIGH",
          "privilegesRequired": "LOW",
          "scope": "CHANGED",
          "userInteraction": "NONE",
          "vectorString": "CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H",
          "version": "3.1"
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    "cvssMetricV40": [
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        "cvssData": {
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          "Recovery": "NOT_DEFINED",
          "Safety": "NOT_DEFINED",
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          "attackRequirements": "PRESENT",
          "attackVector": "NETWORK",
          "availabilityRequirement": "NOT_DEFINED",
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          "baseSeverity": "CRITICAL",
          "confidentialityRequirement": "NOT_DEFINED",
          "exploitMaturity": "NOT_DEFINED",
          "integrityRequirement": "NOT_DEFINED",
          "modifiedAttackComplexity": "NOT_DEFINED",
          "modifiedAttackRequirements": "NOT_DEFINED",
          "modifiedAttackVector": "NOT_DEFINED",
          "modifiedPrivilegesRequired": "NOT_DEFINED",
          "modifiedSubAvailabilityImpact": "NOT_DEFINED",
          "modifiedSubConfidentialityImpact": "NOT_DEFINED",
          "modifiedSubIntegrityImpact": "NOT_DEFINED",
          "modifiedUserInteraction": "NOT_DEFINED",
          "modifiedVulnAvailabilityImpact": "NOT_DEFINED",
          "modifiedVulnConfidentialityImpact": "NOT_DEFINED",
          "modifiedVulnIntegrityImpact": "NOT_DEFINED",
          "privilegesRequired": "LOW",
          "providerUrgency": "NOT_DEFINED",
          "subAvailabilityImpact": "HIGH",
          "subConfidentialityImpact": "HIGH",
          "subIntegrityImpact": "HIGH",
          "userInteraction": "NONE",
          "valueDensity": "NOT_DEFINED",
          "vectorString": "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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X",
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          "vulnAvailabilityImpact": "HIGH",
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    "ssvcV203": [
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            {
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          "role": "CISA Coordinator",
          "timestamp": "2026-04-13T20:16:26.414291Z",
          "version": "2.0.3"
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  "references": [
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      "tags": [
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          "value": "CWE-125"
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}



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