Critical severity · published Feb 24, 2026
CVE-2026-2771
Undefined behavior in the DOM: Core & HTML component
9.8
CVSS
0.8%
EPSS
No
On KEV
Description
Undefined behavior in the DOM: Core & HTML component. This vulnerability was fixed in Firefox 148, Firefox ESR 115.33, Firefox ESR 140.8, Thunderbird 148, and Thunderbird 140.8.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
High
Integrity
High
Availability
High
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.8% · higher than 55% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
FI
Firefox · Mozilla
before 115.33.0; before 148.0; 128.0 before 140.8.0 · source: NVD
TH
Thunderbird · Mozilla
before 140.8.0; before 148.0 · source: NVD
RH
Red Hat Enterprise Linux 10 · Red Hat
All versions, or not specified · source: CISA
RH
Red Hat Enterprise Linux 10.0 Extended Update Support · Red Hat
All versions, or not specified · source: CISA
RH
Red Hat Enterprise Linux 6 · Red Hat
All versions, or not specified · source: CISA
RH
Red Hat Enterprise Linux 7 · Red Hat
All versions, or not specified · source: CISA
RH
Red Hat Enterprise Linux 7 Extended Lifecycle Support · Red Hat
All versions, or not specified · source: CISA
RH
Red Hat Enterprise Linux 8 · Red Hat
All versions, or not specified · source: CISA
RH
Red Hat Enterprise Linux 8.2 Advanced Update Support · Red Hat
All versions, or not specified · source: CISA
RH
Red Hat Enterprise Linux 8.4 Advanced Mission Critical Update Support · Red Hat
All versions, or not specified · source: CISA
RH
Red Hat Enterprise Linux 8.4 Extended Update Support Long-Life Add-On · Red Hat
All versions, or not specified · source: CISA
RH
Red Hat Enterprise Linux 8.6 Advanced Mission Critical Update Support · Red Hat
All versions, or not specified · source: CISA
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-2771
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-2771
Issue Tracking
https://bugzilla.mozilla.org/show_bug.cgi?id=2014593
Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2026-13/
Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2026-14/
Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2026-15/
Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2026-16/
Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2026-17/
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