CVE-2021-43538
Status: ModifiedMedium (4.3)—
By misusing a race in our notification code, an attacker could have forcefully hidden the notification for pages that had received full screen and pointer lock access, which could have been used for spoofing attacks. This vulnerability affects Thunderbird < 91.4.0, Firefox ESR < 91.4.0, and Firefox < 95.
CVSS
- Version: 3.1
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N
- Base score: 4.3
Exploitation probability (EPSS)
- Probability of exploitation in the next 30 days: 1.24%
- Percentile among all scored CVEs: 68
- Score date: 10/7/2026
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 (4)
CWEs
- CWE-362
References
- https://bugzilla.mozilla.org/show_bug.cgi?id=1739091
- https://lists.debian.org/debian-lts-announce/2021/12/msg00030.html
- https://lists.debian.org/debian-lts-announce/2022/01/msg00001.html
- https://security.gentoo.org/glsa/202202-03
- https://security.gentoo.org/glsa/202208-14
- https://www.debian.org/security/2021/dsa-5026
- https://www.debian.org/security/2022/dsa-5034
- https://www.mozilla.org/security/advisories/mfsa2021-52/
- https://www.mozilla.org/security/advisories/mfsa2021-53/
- https://www.mozilla.org/security/advisories/mfsa2021-54/
- https://bugzilla.mozilla.org/show_bug.cgi?id=1739091
- https://lists.debian.org/debian-lts-announce/2021/12/msg00030.html
- https://lists.debian.org/debian-lts-announce/2022/01/msg00001.html
- https://security.gentoo.org/glsa/202202-03
- https://security.gentoo.org/glsa/202208-14
- https://www.debian.org/security/2021/dsa-5026
- https://www.debian.org/security/2022/dsa-5034
- https://www.mozilla.org/security/advisories/mfsa2021-52/
- https://www.mozilla.org/security/advisories/mfsa2021-53/
- https://www.mozilla.org/security/advisories/mfsa2021-54/
Raw JSON (NVD)
Show
{
"id": "CVE-2021-43538",
"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:P/A:N",
"authentication": "NONE",
"integrityImpact": "PARTIAL",
"accessComplexity": "MEDIUM",
"availabilityImpact": "NONE",
"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": 4.3,
"attackVector": "NETWORK",
"baseSeverity": "MEDIUM",
"vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N",
"integrityImpact": "LOW",
"userInteraction": "REQUIRED",
"attackComplexity": "LOW",
"availabilityImpact": "NONE",
"privilegesRequired": "NONE",
"confidentialityImpact": "NONE"
},
"impactScore": 1.4,
"exploitabilityScore": 2.8
}
]
},
"affected": [
{
"source": "security@mozilla.org",
"affectedData": [
{
"vendor": "Mozilla",
"product": "Thunderbird",
"versions": [
{
"status": "affected",
"version": "unspecified",
"lessThan": "91.4.0",
"versionType": "custom"
}
]
},
{
"vendor": "Mozilla",
"product": "Firefox ESR",
"versions": [
{
"status": "affected",
"version": "unspecified",
"lessThan": "91.4.0",
"versionType": "custom"
}
]
},
{
"vendor": "Mozilla",
"product": "Firefox",
"versions": [
{
"status": "affected",
"version": "unspecified",
"lessThan": "95",
"versionType": "custom"
}
]
}
]
}
],
"published": "2021-12-08T22:15:09.677",
"references": [
{
"url": "https://bugzilla.mozilla.org/show_bug.cgi?id=1739091",
"tags": [
"Issue Tracking",
"Permissions Required",
"Vendor Advisory"
],
"source": "security@mozilla.org"
},
{
"url": "https://lists.debian.org/debian-lts-announce/2021/12/msg00030.html",
"tags": [
"Mailing List",
"Third Party Advisory"
],
"source": "security@mozilla.org"
},
{
"url": "https://lists.debian.org/debian-lts-announce/2022/01/msg00001.html",
"tags": [
"Mailing List",
"Third Party Advisory"
],
"source": "security@mozilla.org"
},
{
"url": "https://security.gentoo.org/glsa/202202-03",
"tags": [
"Third Party Advisory"
],
"source": "security@mozilla.org"
},
{
"url": "https://security.gentoo.org/glsa/202208-14",
"tags": [
"Third Party Advisory"
],
"source": "security@mozilla.org"
},
{
"url": "https://www.debian.org/security/2021/dsa-5026",
"tags": [
"Third Party Advisory"
],
"source": "security@mozilla.org"
},
{
"url": "https://www.debian.org/security/2022/dsa-5034",
"tags": [
"Third Party Advisory"
],
"source": "security@mozilla.org"
},
{
"url": "https://www.mozilla.org/security/advisories/mfsa2021-52/",
"tags": [
"Vendor Advisory"
],
"source": "security@mozilla.org"
},
{
"url": "https://www.mozilla.org/security/advisories/mfsa2021-53/",
"tags": [
"Vendor Advisory"
],
"source": "security@mozilla.org"
},
{
"url": "https://www.mozilla.org/security/advisories/mfsa2021-54/",
"tags": [
"Vendor Advisory"
],
"source": "security@mozilla.org"
},
{
"url": "https://bugzilla.mozilla.org/show_bug.cgi?id=1739091",
"tags": [
"Issue Tracking",
"Permissions Required",
"Vendor Advisory"
],
"source": "af854a3a-2127-422b-91ae-364da2661108"
},
{
"url": "https://lists.debian.org/debian-lts-announce/2021/12/msg00030.html",
"tags": [
"Mailing List",
"Third Party Advisory"
],
"source": "af854a3a-2127-422b-91ae-364da2661108"
},
{
"url": "https://lists.debian.org/debian-lts-announce/2022/01/msg00001.html",
"tags": [
"Mailing List",
"Third Party 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://security.gentoo.org/glsa/202208-14",
"tags": [
"Third Party Advisory"
],
"source": "af854a3a-2127-422b-91ae-364da2661108"
},
{
"url": "https://www.debian.org/security/2021/dsa-5026",
"tags": [
"Third Party Advisory"
],
"source": "af854a3a-2127-422b-91ae-364da2661108"
},
{
"url": "https://www.debian.org/security/2022/dsa-5034",
"tags": [
"Third Party Advisory"
],
"source": "af854a3a-2127-422b-91ae-364da2661108"
},
{
"url": "https://www.mozilla.org/security/advisories/mfsa2021-52/",
"tags": [
"Vendor Advisory"
],
"source": "af854a3a-2127-422b-91ae-364da2661108"
},
{
"url": "https://www.mozilla.org/security/advisories/mfsa2021-53/",
"tags": [
"Vendor Advisory"
],
"source": "af854a3a-2127-422b-91ae-364da2661108"
},
{
"url": "https://www.mozilla.org/security/advisories/mfsa2021-54/",
"tags": [
"Vendor Advisory"
],
"source": "af854a3a-2127-422b-91ae-364da2661108"
}
],
"vulnStatus": "Modified",
"weaknesses": [
{
"type": "Primary",
"source": "nvd@nist.gov",
"description": [
{
"lang": "en",
"value": "CWE-362"
}
]
}
],
"descriptions": [
{
"lang": "en",
"value": "By misusing a race in our notification code, an attacker could have forcefully hidden the notification for pages that had received full screen and pointer lock access, which could have been used for spoofing attacks. This vulnerability affects Thunderbird < 91.4.0, Firefox ESR < 91.4.0, and Firefox < 95."
},
{
"lang": "es",
"value": "Mediante el uso indebido de una carrera en nuestro código de notificación, un atacante podría haber ocultado a la fuerza la notificación de las páginas que habían recibido acceso a pantalla completa y bloqueo de puntero, lo que podría haber sido usado para ataques de suplantación de identidad. Esta vulnerabilidad afecta a Thunderbird versiones anteriores a 91.4.0, Firefox ESR versiones anteriores a 91.4.0 y Firefox versiones anteriores a 95"
}
],
"lastModified": "2026-06-17T04:11:05.583",
"configurations": [
{
"nodes": [
{
"negate": false,
"cpeMatch": [
{
"criteria": "cpe:2.3:a:mozilla:firefox:*:*:*:*:*:*:*:*",
"vulnerable": true,
"matchCriteriaId": "83D69E34-EB94-49ED-9FA1-F68400971726",
"versionEndExcluding": "95.0"
},
{
"criteria": "cpe:2.3:a:mozilla:firefox_esr:*:*:*:*:*:*:*:*",
"vulnerable": true,
"matchCriteriaId": "F90A171C-1670-4EBA-9DE0-E31E8F3CD0FA",
"versionEndExcluding": "91.4.0"
},
{
"criteria": "cpe:2.3:a:mozilla:thunderbird:*:*:*:*:*:*:*:*",
"vulnerable": true,
"matchCriteriaId": "6F0BE95D-5BE5-49F7-92BA-CF3A3920D447",
"versionEndExcluding": "91.4.0"
}
],
"operator": "OR"
}
]
},
{
"nodes": [
{
"negate": false,
"cpeMatch": [
{
"criteria": "cpe:2.3:o:debian:debian_linux:9.0:*:*:*:*:*:*:*",
"vulnerable": true,
"matchCriteriaId": "DEECE5FC-CACF-4496-A3E7-164736409252"
},
{
"criteria": "cpe:2.3:o:debian:debian_linux:10.0:*:*:*:*:*:*:*",
"vulnerable": true,
"matchCriteriaId": "07B237A9-69A3-4A9C-9DA0-4E06BD37AE73"
},
{
"criteria": "cpe:2.3:o:debian:debian_linux:11.0:*:*:*:*:*:*:*",
"vulnerable": true,
"matchCriteriaId": "FA6FEEC2-9F11-4643-8827-749718254FED"
}
],
"operator": "OR"
}
]
}
],
"sourceIdentifier": "security@mozilla.org"
}