HighFix available
firefox-esr, thunderbird — security advisory
When Responsive Design Mode was enabled, it used references to objects that were previously freed. We presume that with enough effort this could have been exploited to run arbitrary code. This vulnerability affects Firefox ESR < 78.10, Thunderbird < 78.10, and Firefox < 88.
- Products
- firefox-esr, thunderbird
- Affected versions
- Not specified
- Fixed versions
- 1:78.10.0-1, 78.10.0esr-1
- CVEs
- CVE-2021-23995
- Confirmed fixed CVEs
- Not specified
- Updated in this feed
- 1 Nov 2026, 00:02 UTC · Revision 1
Source evidence
When Responsive Design Mode was enabled, it used references to objects that were previously freed. We presume that with enough effort this could have been exploited to run arbitrary code. This vulnerability affects Firefox ESR < 78.10, Thunderbird < 78.10, and Firefox < 88.
osv:DEBIAN-CVE-2021-23995
firefox-esr
Fixed versions: 78.10.0esr-1
firefox-esr
Fixed versions: 78.10.0esr-1
firefox-esr
Fixed versions: 78.10.0esr-1
thunderbird
Fixed versions: 1:78.10.0-1
thunderbird
Fixed versions: 1:78.10.0-1
thunderbird
Fixed versions: 1:78.10.0-1
Complete source record
{
"id": "07769a45ca74d6885aabfe1c3e8ba4f83dab5f84754b4b81950ec852f7406a98",
"url": "https://osv.dev/vulnerability/DEBIAN-CVE-2021-23995",
"method": "structured",
"payload": {
"kind": "advisory",
"title": "DEBIAN-CVE-2021-23995",
"summary": "When Responsive Design Mode was enabled, it used references to objects that were previously freed. We presume that with enough effort this could have been exploited to run arbitrary code. This vulnerability affects Firefox ESR < 78.10, Thunderbird < 78.10, and Firefox < 88.",
"evidence": "osv:DEBIAN-CVE-2021-23995",
"products": [
{
"name": {
"value": "firefox-esr",
"evidence": "/affected/0/package/name"
},
"prerequisites": [],
"fixed_versions": [
{
"value": "78.10.0esr-1",
"evidence": "/affected/0/ranges"
}
],
"affected_versions": []
},
{
"name": {
"value": "firefox-esr",
"evidence": "/affected/1/package/name"
},
"prerequisites": [],
"fixed_versions": [
{
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}
],
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},
{
"name": {
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},
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}
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},
{
"name": {
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},
"prerequisites": [],
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{
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"evidence": "/affected/3/ranges"
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"affected_versions": []
},
{
"name": {
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}
],
"affected_versions": []
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{
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"evidence": "/affected/5/ranges"
}
],
"affected_versions": []
}
],
"severity": "high",
"structured": {
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"aliases": [
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],
"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": [
{
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"events": [
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],
"package": {
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"purl": "pkg:deb/debian/firefox-esr?arch=source&distro=bookworm",
"ecosystem": "Debian:12"
},
"database_specific": {
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},
"ecosystem_specific": {
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}
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{
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"ecosystem": "Debian:13"
},
"database_specific": {
"source": "https://storage.googleapis.com/debian-osv/debian-cve-osv/DEBIAN-CVE-2021-23995.json"
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{
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],
"package": {
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"ecosystem": "Debian:14"
},
"database_specific": {
"source": "https://storage.googleapis.com/debian-osv/debian-cve-osv/DEBIAN-CVE-2021-23995.json"
},
"ecosystem_specific": {
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{
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"package": {
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"ecosystem": "Debian:12"
},
"database_specific": {
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},
"ecosystem_specific": {
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}
},
{
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],
"package": {
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"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-2021-23995.json"
},
"ecosystem_specific": {
"urgency": "not yet assigned"
}
},
{
"ranges": [
{
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},
{
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],
"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-2021-23995.json"
},
"ecosystem_specific": {
"urgency": "not yet assigned"
}
}
],
"modified": "2026-10-23T18:02:52.223564333Z",
"provider": "osv",
"upstream": [
"CVE-2021-23995"
],
"references": [
"https://security-tracker.debian.org/tracker/CVE-2021-23995"
]
},
"related_cves": [
{
"value": "CVE-2021-23995",
"evidence": "/upstream"
}
],
"security_relevant": true,
"severity_evidence": "/severity/0/score"
},
"source_id": "core-osv",
"document_id": 419758,
"published_at": "2021-06-24T14:15:09.357+00:00"
}