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CVE-2021-29977

Status: ModifiedHigh (8.8)—

Mozilla developers reported memory safety bugs present in Firefox 89. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. This vulnerability affects Firefox < 90.

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 (1)

Mozilla — Firefox

CWEs

References

Raw JSON (NVD)

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{
  "id": "CVE-2021-29977",
  "cveTags": [],
  "metrics": {
    "cvssMetricV2": [
      {
        "type": "Primary",
        "source": "nvd@nist.gov",
        "cvssData": {
          "version": "2.0",
          "baseScore": 6.8,
          "accessVector": "NETWORK",
          "vectorString": "AV:N/AC:M/Au:N/C:P/I:P/A:P",
          "authentication": "NONE",
          "integrityImpact": "PARTIAL",
          "accessComplexity": "MEDIUM",
          "availabilityImpact": "PARTIAL",
          "confidentialityImpact": "PARTIAL"
        },
        "acInsufInfo": false,
        "impactScore": 6.4,
        "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": 8.8,
          "attackVector": "NETWORK",
          "baseSeverity": "HIGH",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H",
          "integrityImpact": "HIGH",
          "userInteraction": "REQUIRED",
          "attackComplexity": "LOW",
          "availabilityImpact": "HIGH",
          "privilegesRequired": "NONE",
          "confidentialityImpact": "HIGH"
        },
        "impactScore": 5.9,
        "exploitabilityScore": 2.8
      }
    ]
  },
  "affected": [
    {
      "source": "security@mozilla.org",
      "affectedData": [
        {
          "vendor": "Mozilla",
          "product": "Firefox",
          "versions": [
            {
              "status": "affected",
              "version": "unspecified",
              "lessThan": "90",
              "versionType": "custom"
            }
          ]
        }
      ]
    }
  ],
  "published": "2021-08-05T20:15:08.817",
  "references": [
    {
      "url": "https://bugzilla.mozilla.org/buglist.cgi?bug_id=1665836%2C1686138%2C1704316%2C1706314%2C1709931%2C1712084%2C1712357%2C1714066",
      "tags": [
        "Issue Tracking",
        "Vendor Advisory"
      ],
      "source": "security@mozilla.org"
    },
    {
      "url": "https://security.gentoo.org/glsa/202202-03",
      "tags": [
        "Third Party Advisory"
      ],
      "source": "security@mozilla.org"
    },
    {
      "url": "https://www.mozilla.org/security/advisories/mfsa2021-28/",
      "tags": [
        "Vendor Advisory"
      ],
      "source": "security@mozilla.org"
    },
    {
      "url": "https://bugzilla.mozilla.org/buglist.cgi?bug_id=1665836%2C1686138%2C1704316%2C1706314%2C1709931%2C1712084%2C1712357%2C1714066",
      "tags": [
        "Issue Tracking",
        "Vendor Advisory"
      ],
      "source": "af854a3a-2127-422b-91ae-364da2661108"
    },
    {
      "url": "https://security.gentoo.org/glsa/202202-03",
      "tags": [
        "Third Party Advisory"
      ],
      "source": "af854a3a-2127-422b-91ae-364da2661108"
    },
    {
      "url": "https://www.mozilla.org/security/advisories/mfsa2021-28/",
      "tags": [
        "Vendor Advisory"
      ],
      "source": "af854a3a-2127-422b-91ae-364da2661108"
    }
  ],
  "vulnStatus": "Modified",
  "weaknesses": [
    {
      "type": "Primary",
      "source": "nvd@nist.gov",
      "description": [
        {
          "lang": "en",
          "value": "CWE-787"
        }
      ]
    }
  ],
  "descriptions": [
    {
      "lang": "en",
      "value": "Mozilla developers reported memory safety bugs present in Firefox 89. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. This vulnerability affects Firefox < 90."
    },
    {
      "lang": "es",
      "value": "Los desarrolladores de Mozilla informaron de fallos de seguridad de memoria presentes en Firefox 89. Algunos de estos fallos mostraban evidencias de corrupción de memoria y suponemos que con suficiente esfuerzo algunos de ellos podrían haber sido explotados para ejecutar código arbitrario. Esta vulnerabilidad afecta a Firefox versiones anteriores a 90"
    }
  ],
  "lastModified": "2026-06-17T03:48:32.633",
  "configurations": [
    {
      "nodes": [
        {
          "negate": false,
          "cpeMatch": [
            {
              "criteria": "cpe:2.3:a:mozilla:firefox:*:*:*:*:*:*:*:*",
              "vulnerable": true,
              "matchCriteriaId": "FA0BA5A6-A40E-418E-A536-9A14711264B7",
              "versionEndExcluding": "90.0"
            }
          ],
          "operator": "OR"
        }
      ]
    }
  ],
  "sourceIdentifier": "security@mozilla.org"
}