HighFix available
firefox-esr, thunderbird — security advisory
Mozilla developers reported memory safety bugs present in code shared between Firefox and Thunderbird. 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 Thunderbird < 78.12, Firefox ESR < 78.12, and Firefox < 90.
- Products
- firefox-esr, thunderbird
- Affected versions
- Not specified
- Fixed versions
- 1:78.12.0-1, 78.12.0esr-1
- CVEs
- CVE-2021-29976
- Confirmed fixed CVEs
- Not specified
- Updated in this feed
- 1 Nov 2026, 00:33 UTC · Revision 1
Source evidence
Mozilla developers reported memory safety bugs present in code shared between Firefox and Thunderbird. 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 Thunderbird < 78.12, Firefox ESR < 78.12, and Firefox < 90.
osv:DEBIAN-CVE-2021-29976
firefox-esr
Fixed versions: 78.12.0esr-1
firefox-esr
Fixed versions: 78.12.0esr-1
firefox-esr
Fixed versions: 78.12.0esr-1
thunderbird
Fixed versions: 1:78.12.0-1
thunderbird
Fixed versions: 1:78.12.0-1
thunderbird
Fixed versions: 1:78.12.0-1
Complete source record
{
"id": "13fc7d5c2694731a5ca3184fa2c26f8835dfa9d42a5b505502a26fea6019e1cb",
"url": "https://osv.dev/vulnerability/DEBIAN-CVE-2021-29976",
"method": "structured",
"payload": {
"kind": "advisory",
"title": "DEBIAN-CVE-2021-29976",
"summary": "Mozilla developers reported memory safety bugs present in code shared between Firefox and Thunderbird. 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 Thunderbird < 78.12, Firefox ESR < 78.12, and Firefox < 90.",
"evidence": "osv:DEBIAN-CVE-2021-29976",
"products": [
{
"name": {
"value": "firefox-esr",
"evidence": "/affected/0/package/name"
},
"prerequisites": [],
"fixed_versions": [
{
"value": "78.12.0esr-1",
"evidence": "/affected/0/ranges"
}
],
"affected_versions": []
},
{
"name": {
"value": "firefox-esr",
"evidence": "/affected/1/package/name"
},
"prerequisites": [],
"fixed_versions": [
{
"value": "78.12.0esr-1",
"evidence": "/affected/1/ranges"
}
],
"affected_versions": []
},
{
"name": {
"value": "firefox-esr",
"evidence": "/affected/2/package/name"
},
"prerequisites": [],
"fixed_versions": [
{
"value": "78.12.0esr-1",
"evidence": "/affected/2/ranges"
}
],
"affected_versions": []
},
{
"name": {
"value": "thunderbird",
"evidence": "/affected/3/package/name"
},
"prerequisites": [],
"fixed_versions": [
{
"value": "1:78.12.0-1",
"evidence": "/affected/3/ranges"
}
],
"affected_versions": []
},
{
"name": {
"value": "thunderbird",
"evidence": "/affected/4/package/name"
},
"prerequisites": [],
"fixed_versions": [
{
"value": "1:78.12.0-1",
"evidence": "/affected/4/ranges"
}
],
"affected_versions": []
},
{
"name": {
"value": "thunderbird",
"evidence": "/affected/5/package/name"
},
"prerequisites": [],
"fixed_versions": [
{
"value": "1:78.12.0-1",
"evidence": "/affected/5/ranges"
}
],
"affected_versions": []
}
],
"severity": "high",
"structured": {
"id": "DEBIAN-CVE-2021-29976",
"aliases": [
"DEBIAN-CVE-2021-29976"
],
"metrics": [
{
"type": "CVSS_V3",
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H"
}
],
"affected": [
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "0"
},
{
"fixed": "78.12.0esr-1"
}
]
}
],
"package": {
"name": "firefox-esr",
"purl": "pkg:deb/debian/firefox-esr?arch=source&distro=bookworm",
"ecosystem": "Debian:12"
},
"database_specific": {
"source": "https://storage.googleapis.com/debian-osv/debian-cve-osv/DEBIAN-CVE-2021-29976.json"
},
"ecosystem_specific": {
"urgency": "not yet assigned"
}
},
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "0"
},
{
"fixed": "78.12.0esr-1"
}
]
}
],
"package": {
"name": "firefox-esr",
"purl": "pkg:deb/debian/firefox-esr?arch=source&distro=trixie",
"ecosystem": "Debian:13"
},
"database_specific": {
"source": "https://storage.googleapis.com/debian-osv/debian-cve-osv/DEBIAN-CVE-2021-29976.json"
},
"ecosystem_specific": {
"urgency": "not yet assigned"
}
},
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
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{
"fixed": "78.12.0esr-1"
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],
"package": {
"name": "firefox-esr",
"purl": "pkg:deb/debian/firefox-esr?arch=source&distro=forky",
"ecosystem": "Debian:14"
},
"database_specific": {
"source": "https://storage.googleapis.com/debian-osv/debian-cve-osv/DEBIAN-CVE-2021-29976.json"
},
"ecosystem_specific": {
"urgency": "not yet assigned"
}
},
{
"ranges": [
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"events": [
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],
"package": {
"name": "thunderbird",
"purl": "pkg:deb/debian/thunderbird?arch=source&distro=bookworm",
"ecosystem": "Debian:12"
},
"database_specific": {
"source": "https://storage.googleapis.com/debian-osv/debian-cve-osv/DEBIAN-CVE-2021-29976.json"
},
"ecosystem_specific": {
"urgency": "not yet assigned"
}
},
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "0"
},
{
"fixed": "1:78.12.0-1"
}
]
}
],
"package": {
"name": "thunderbird",
"purl": "pkg:deb/debian/thunderbird?arch=source&distro=trixie",
"ecosystem": "Debian:13"
},
"database_specific": {
"source": "https://storage.googleapis.com/debian-osv/debian-cve-osv/DEBIAN-CVE-2021-29976.json"
},
"ecosystem_specific": {
"urgency": "not yet assigned"
}
},
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "0"
},
{
"fixed": "1:78.12.0-1"
}
]
}
],
"package": {
"name": "thunderbird",
"purl": "pkg:deb/debian/thunderbird?arch=source&distro=forky",
"ecosystem": "Debian:14"
},
"database_specific": {
"source": "https://storage.googleapis.com/debian-osv/debian-cve-osv/DEBIAN-CVE-2021-29976.json"
},
"ecosystem_specific": {
"urgency": "not yet assigned"
}
}
],
"modified": "2026-10-23T18:03:26.069349635Z",
"provider": "osv",
"upstream": [
"CVE-2021-29976"
],
"references": [
"https://security-tracker.debian.org/tracker/CVE-2021-29976"
]
},
"related_cves": [
{
"value": "CVE-2021-29976",
"evidence": "/upstream"
}
],
"security_relevant": true,
"severity_evidence": "/severity/0/score"
},
"source_id": "core-osv",
"document_id": 421497,
"published_at": "2021-08-05T20:15:08.773+00:00"
}