Home/CVE/Undefined behavior in the DOM: Core & HTML component. This vulnerability was fixed in Firefox 148, Firefox ESR 115.33, F
CVE

CVE-2026-2771

Undefined behavior in the DOM: Core & HTML component. This vulnerability was fixed in Firefox 148, Firefox ESR 115.33, F

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.

CRITICAL · CVSS 9.8 EPSS 0.00029
Schedule remediation
  • SSVC automatable: yes - attacks can be scripted at scale
  • CVSS base score ≥ 7.0
Sigma rules1 YARA rules0
⬡

Weakness Classification

CWE-125Out-of-bounds Read
▤

Affected Products & Versions

5
mozilla firefox< 115.33.0
mozilla firefox< 148.0
mozilla firefox>= 128.0 and < 140.8.0
mozilla thunderbird< 140.8.0
mozilla thunderbird< 148.0
◈

Sigma Hunt Rules

1
Exact rules name this CVE ID. Product rules name an affected product in their title. Related rules cover techniques used by actors who exploited this CVE. Showing the most relevant matches; the complete related set is on the full drill-down.
producthighSQLite Firefox Profile Data DB Access
▣

Scoring & Timeline

9.8
CRITICAL · CVSS v3.1 · security@mozilla.org
View on NVD
Attack Vector
Network Adjacent Local Physical
Attack Complexity
Low High
Privileges Required
None Low High
User Interaction
None Required
Scope
Unchanged Changed
Confidentiality
None Low High
Integrity
None Low High
Availability
None Low High
Published to NVD24 Feb 2026 · 02:16 PM
CVSS VectorCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
SSVC triage · cisa-vulnrichment
Exploitation
none
Automatable
yes
Technical impact
total
SSVC asks the questions that actually drive patch urgency: is it being exploited, can attacks be automated, and how total is the impact.
⚑

Vendor Advisories

30
suse-csafopenSUSE-SU-2026:20391-1
suse-csafopenSUSE-SU-2026:20365-1
suse-csafSUSE-SU-2026:0880-1
suse-csafSUSE-SU-2026:0871-1
suse-csafSUSE-SU-2026:0812-1
🔗

References & Sources

6
Source URLs (vendor pages, mailing lists, write-ups). Exploit/PoC links are in their own section above to avoid duplication.
https://bugzilla.mozilla.org/show_bug.cgi?id=2014593Issue TrackingPermissions Required
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/Vendor Advisory
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