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CVE-2021-29945

Status: ModifiedMedium (6.5)—

The WebAssembly JIT could miscalculate the size of a return type, which could lead to a null read and result in a crash. *Note: This issue only affected x86-32 platforms. Other platforms are unaffected.*. This vulnerability affects Firefox ESR < 78.10, Thunderbird < 78.10, and Firefox < 88.

CVSS

Exploitation probability (EPSS)

EPSS (Exploit Prediction Scoring System, FIRST) estimates how likely a vulnerability is to be exploited in the wild within 30 days. It complements CVSS (impact) and CISA KEV (confirmed exploitation).

Affected technologies (3)

Mozilla — FirefoxMozilla — Firefox ESRMozilla — Thunderbird

CWEs

References

Raw JSON (NVD)

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{
  "id": "CVE-2021-29945",
  "cveTags": [],
  "metrics": {
    "cvssMetricV2": [
      {
        "type": "Primary",
        "source": "nvd@nist.gov",
        "cvssData": {
          "version": "2.0",
          "baseScore": 4.3,
          "accessVector": "NETWORK",
          "vectorString": "AV:N/AC:M/Au:N/C:N/I:N/A:P",
          "authentication": "NONE",
          "integrityImpact": "NONE",
          "accessComplexity": "MEDIUM",
          "availabilityImpact": "PARTIAL",
          "confidentialityImpact": "NONE"
        },
        "acInsufInfo": false,
        "impactScore": 2.9,
        "baseSeverity": "MEDIUM",
        "obtainAllPrivilege": false,
        "exploitabilityScore": 8.6,
        "obtainUserPrivilege": false,
        "obtainOtherPrivilege": false,
        "userInteractionRequired": true
      }
    ],
    "cvssMetricV31": [
      {
        "type": "Primary",
        "source": "nvd@nist.gov",
        "cvssData": {
          "scope": "UNCHANGED",
          "version": "3.1",
          "baseScore": 6.5,
          "attackVector": "NETWORK",
          "baseSeverity": "MEDIUM",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H",
          "integrityImpact": "NONE",
          "userInteraction": "REQUIRED",
          "attackComplexity": "LOW",
          "availabilityImpact": "HIGH",
          "privilegesRequired": "NONE",
          "confidentialityImpact": "NONE"
        },
        "impactScore": 3.6,
        "exploitabilityScore": 2.8
      }
    ]
  },
  "affected": [
    {
      "source": "security@mozilla.org",
      "affectedData": [
        {
          "vendor": "Mozilla",
          "product": "Firefox ESR",
          "versions": [
            {
              "status": "affected",
              "version": "unspecified",
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              "versionType": "custom"
            }
          ]
        },
        {
          "vendor": "Mozilla",
          "product": "Thunderbird",
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              "status": "affected",
              "version": "unspecified",
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              "versionType": "custom"
            }
          ]
        },
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          "vendor": "Mozilla",
          "product": "Firefox",
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              "version": "unspecified",
              "lessThan": "88",
              "versionType": "custom"
            }
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  ],
  "published": "2021-06-24T14:15:09.763",
  "references": [
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      "url": "https://bugzilla.mozilla.org/show_bug.cgi?id=1700690",
      "tags": [
        "Issue Tracking",
        "Permissions Required",
        "Vendor Advisory"
      ],
      "source": "security@mozilla.org"
    },
    {
      "url": "https://www.mozilla.org/security/advisories/mfsa2021-14/",
      "tags": [
        "Release Notes",
        "Vendor Advisory"
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      "source": "security@mozilla.org"
    },
    {
      "url": "https://www.mozilla.org/security/advisories/mfsa2021-15/",
      "tags": [
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        "Vendor Advisory"
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      "source": "security@mozilla.org"
    },
    {
      "url": "https://www.mozilla.org/security/advisories/mfsa2021-16/",
      "tags": [
        "Release Notes",
        "Vendor Advisory"
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      "source": "security@mozilla.org"
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      "url": "https://bugzilla.mozilla.org/show_bug.cgi?id=1700690",
      "tags": [
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      "source": "af854a3a-2127-422b-91ae-364da2661108"
    },
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      "url": "https://www.mozilla.org/security/advisories/mfsa2021-14/",
      "tags": [
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        "Vendor Advisory"
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      "source": "af854a3a-2127-422b-91ae-364da2661108"
    },
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      "url": "https://www.mozilla.org/security/advisories/mfsa2021-15/",
      "tags": [
        "Release Notes",
        "Vendor Advisory"
      ],
      "source": "af854a3a-2127-422b-91ae-364da2661108"
    },
    {
      "url": "https://www.mozilla.org/security/advisories/mfsa2021-16/",
      "tags": [
        "Release Notes",
        "Vendor Advisory"
      ],
      "source": "af854a3a-2127-422b-91ae-364da2661108"
    }
  ],
  "vulnStatus": "Modified",
  "weaknesses": [
    {
      "type": "Primary",
      "source": "nvd@nist.gov",
      "description": [
        {
          "lang": "en",
          "value": "CWE-682"
        }
      ]
    }
  ],
  "descriptions": [
    {
      "lang": "en",
      "value": "The WebAssembly JIT could miscalculate the size of a return type, which could lead to a null read and result in a crash. *Note: This issue only affected x86-32 platforms. Other platforms are unaffected.*. This vulnerability affects Firefox ESR < 78.10, Thunderbird < 78.10, and Firefox < 88."
    },
    {
      "lang": "es",
      "value": "El JIT de WebAssembly podía calcular mal el tamaño de un tipo de retorno, lo que podía conllevar a una lectura nula y resultar en un bloqueo. *Nota: Este problema sólo afectaba a las plataformas x86-32. Otras plataformas no están afectadas. Esta vulnerabilidad afecta a Firefox ESR versiones anteriores a 78.10, Thunderbird versiones anteriores a 78.10 y Firefox versiones anteriores a 88"
    }
  ],
  "lastModified": "2026-06-17T03:48:29.313",
  "configurations": [
    {
      "nodes": [
        {
          "negate": false,
          "cpeMatch": [
            {
              "criteria": "cpe:2.3:a:mozilla:firefox:*:*:*:*:*:*:x86:*",
              "vulnerable": true,
              "matchCriteriaId": "93A024F9-E2A3-4F13-83A3-879EAC032592",
              "versionEndExcluding": "88.0"
            },
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            },
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          "operator": "OR"
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  "sourceIdentifier": "security@mozilla.org"
}