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Thunderbird CVE-2026-2778

CRITICAL
Buffer Overflow (CWE-119)
2026-02-24 security@mozilla.org
Buffer Overflow Mozilla Thunderbird
10.0
CVSS 3.1 · NVD
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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata – not a confirmed exploit chain

  1. Access
    Send malicious HTML document
  2. Exploit
    Trigger boundary condition in DOM parser
  3. Execution
    Escape sandbox environment
  4. Impact
    Execute arbitrary code with system privileges

Vulnerability Assessment

Weakness
CWE
CWE-119
OWASP Top 10:2025
A06:2021 - Vulnerable and Outdated Components
ASVS 5.0
V15 - Secure Coding and Architecture Bounds checking, buffer size validation
MITRE ATT&CK

2 techniques across 2 tactics: Execution, Privilege Escalation

The technique list with ATT&CK links and the kill-chain view is part of the Basic plan and up.

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Exploitation Conditions

No special conditions — remote unauthenticated exploitation against default Firefox or Thunderbird installations by opening a crafted HTML document in the browser.
Impact

CVSS 10.0. Five sandbox escapes in a single release is exceptional — indicates a comprehensive security audit identified systemic sandbox weaknesses.
Exploit ScenarioDerived

DOM manipulation triggers boundary error that escapes the content process sandbox.
Act Now Prioritize within 24-48h. Why: CRITICAL severity.
Patch available 0.1% exploitation probability (EPSS)

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AnalysisAIv1 – Mar 12, 2026

Sandbox escape via DOM Core & HTML component in Firefox before 148. CVSS 10.0 — fifth sandbox escape in this release.

Earlier versions of this analysis (1)
v1 Mar 12, 2026 - 21:55 CVSS 10.0

Fifth sandbox escape in Firefox 148 — through DOM Core.

RemediationAI

Update Firefox to 148+ immediately.

Affects your stack

Find out whether the stacks and servers you run are on an affected version.

Checking this CVE against your own stacks and servers is part of the Basic plan and up.

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Technical ContextAI · show details

CWE-119 boundary error in DOM Core & HTML enabling sandbox escape. The DOM implementation allows operations that breach process boundaries.

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  • Exploit and PoC references, threat intelligence from 22 sources
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Severity by source

NVD PRIMARY 10.0 CRITICAL
AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H
SUSE 8.3 HIGH
AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H
Red Hat 7.5 HIGH

Primary rating from NVD.

CVSS VectorNVD

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Changed
Confidentiality
High
Integrity
High
Availability
High

Lifecycle Timeline

2
Patch released
Apr 10, 2026 - 08:30 nvd
Patch available
CVE Published
Feb 24, 2026 - 14:16 nvd
CRITICAL 10.0

DescriptionNVD

Sandbox escape due to incorrect boundary conditions in the DOM: Core & HTML component. This vulnerability affects Firefox < 148, Firefox ESR < 115.33, Firefox ESR < 140.8, Thunderbird < 148, and Thunderbird < 140.8.

Executive ViewAI

Why It Matters

A critical sandbox escape vulnerability (CVSS 10.0) in Firefox and Thunderbird allows attackers to execute arbitrary code with full system privileges by exploiting DOM boundary condition flaws. Organizations with users running affected browser versions face immediate risk of endpoint compromise and potential lateral movement into corporate networks.

Business Impact: Severe
Compensating Controls

Implement browser isolation technology (cloud-based or local sandboxing); disable JavaScript in Thunderbird email rendering; enforce content filtering at network perimeter to block malicious HTML/DOM payloads; restrict Firefox/Thunderbird execution on high-risk systems via application whitelisting; increase endpoint detection and response (EDR) monitoring for process injection and privilege escalation; consider blocking external web browsing until patched. Monitor vendor release channels daily for patch availability.

Threat Intelligence Overview

EPSS Score
0.1%
Top 78% exploitable
Data Quality
5 sources
Confidence: Medium
NVD CVE.org EPSS Vendor VulDB

How this decision was reached

The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.

SignalValue
Severity CRITICAL
CISA KEV No
Public POC No
EPSS 0.1%
Patch available Yes
Active threat No
Deciding rule
CRITICAL severity
What every action level means
Emergency Immediate action required. Criteria: CRITICAL + in CISA KEV (actively exploited) without patch, OR CRITICAL + EPSS > 30% without patch, OR CRITICAL + active threat signals without patch.
Act Now Prioritize within 24-48h. Criteria: in KEV with patch available, OR CRITICAL + public POC, OR HIGH + EPSS > 10%, OR CRITICAL + active threat, OR any CRITICAL severity.
This Week Schedule remediation this week. Criteria: HIGH severity (CVSS 7.0-8.9). Patch within normal change window.
This Month Plan within 30 days. Criteria: MEDIUM severity (CVSS 4.0-6.9), lower exploitation probability. Include in regular patch cycle.
Monitor Track and reassess. Criteria: LOW severity (CVSS 0.1-3.9), minimal exploitation risk. No immediate action needed.

SSVC AssessmentENISA

SSVC Decision· derived
Out-of-Cycle
Exploitation· derived
None
System Exposure· derived
Open
Automatable· derived
Yes
Human Impact
Very High

Priority Score

50
Low Medium High Critical
KEV: 0
EPSS: 0
CVSS: +50
PoC: 0
Weaponized: 0
Threat intel: 0
Gov advisory: 0

Attack Technique

Buffer Overflow HIGH

A buffer overflow occurs when a program writes more data to a memory buffer than it was allocated to hold, causing the excess data to spill into adjacent memory regions.

Affected Products (CPE)NVD

cpe:2.3:a:mozilla:firefox:*:*:*:*:esr:*:*:*
cpe:2.3:a:mozilla:firefox:*:*:*:*:-:*:*:*
cpe:2.3:a:mozilla:firefox:*:*:*:*:esr:*:*:*
cpe:2.3:a:mozilla:thunderbird:*:*:*:*:esr:*:*:*
cpe:2.3:a:mozilla:thunderbird:*:*:*:*:-:*:*:*

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CVE-2015-0816 MEDIUM POC
5.0 Apr 01

Mozilla Firefox before 37.0, Firefox ESR 31.x before 31.6, and Thunderbird before 31.6 do not properly restrict resource
CVE-2013-2566 MEDIUM POC
5.9 Mar 15

The RC4 algorithm, as used in the TLS protocol and SSL protocol, has many single-byte biases, which makes it easier for

Same weakness CWE-119 – Buffer Overflow

View all
CVE-2020-0796 CRITICAL POC
10.0
CVE-2017-11882 HIGH POC
7.8
CVE-2014-6332 HIGH POC
8.8
CVE-2015-2426 HIGH POC
8.8
CVE-2013-3918 HIGH POC
8.8
CVE-2023-4966 HIGH POC
7.5
CVE-2017-11774 HIGH POC
7.8
CVE-2013-3660 HIGH POC
7.8

Same technique Buffer Overflow

View all
CVE-2017-7269 CRITICAL POC
9.8
CVE-2015-5119 CRITICAL POC
9.8
CVE-2015-3113 CRITICAL POC
9.8
CVE-2011-2462 CRITICAL POC
9.8
CVE-2019-11043 CRITICAL POC
9.8
CVE-2009-0927 HIGH POC
8.8
CVE-2012-1889 HIGH POC
8.8

Vendor StatusVendor

SUSE

Severity: High
Product Status
Container suse/sl-micro/6.0/baremetal-os-container:2.1.3-6.61 Container suse/sl-micro/6.0/base-os-container:2.1.3-7.27 Container suse/sl-micro/6.0/kvm-os-container:2.1.3-6.52 Container suse/sl-micro/6.0/rt-os-container:2.1.3-7.63 Container suse/sl-micro/6.0/toolbox:13.2-9.16 Image SL-Micro Affected
Image SL-Micro-BYOS-GCE Image SUSE-Multi-Linux-Manager-Proxy-BYOS-GCE Image SUSE-Multi-Linux-Manager-Server-BYOS-GCE Affected
Image SLES12-SP5-SAP-Azure-LI-BYOS-Production Image SLES12-SP5-SAP-Azure-VLI-BYOS-Production Affected
Image SLES15-SP5-SAP-Azure-LI-BYOS Image SLES15-SP5-SAP-Azure-LI-BYOS-Production Image SLES15-SP5-SAP-Azure-VLI-BYOS Image SLES15-SP5-SAP-Azure-VLI-BYOS-Production Image SLES15-SP7-SAP-Azure-LI-BYOS-Production Image SLES15-SP7-SAP-Azure-VLI-BYOS-Production Affected
SUSE Liberty Linux 8 Fixed

References

Advisories & patches
ADVISORY https://access.redhat.com/errata/RHSA-2026:3338 ADVISORY https://access.redhat.com/errata/RHSA-2026:3339 ADVISORY https://access.redhat.com/errata/RHSA-2026:3361 ADVISORY https://access.redhat.com/errata/RHSA-2026:3491 ADVISORY https://access.redhat.com/errata/RHSA-2026:3492 ADVISORY https://access.redhat.com/errata/RHSA-2026:3493 ADVISORY https://access.redhat.com/errata/RHSA-2026:3494 ADVISORY https://access.redhat.com/errata/RHSA-2026:3495 ADVISORY https://access.redhat.com/errata/RHSA-2026:3496 ADVISORY https://access.redhat.com/errata/RHSA-2026:3497 ADVISORY https://access.redhat.com/errata/RHSA-2026:3515 ADVISORY https://access.redhat.com/errata/RHSA-2026:3516 ADVISORY https://access.redhat.com/errata/RHSA-2026:3517 ADVISORY https://access.redhat.com/errata/RHSA-2026:3976 ADVISORY https://access.redhat.com/errata/RHSA-2026:3978 ADVISORY https://access.redhat.com/errata/RHSA-2026:3979 ADVISORY https://access.redhat.com/errata/RHSA-2026:3980 ADVISORY https://access.redhat.com/errata/RHSA-2026:3981 ADVISORY https://access.redhat.com/errata/RHSA-2026:3982 ADVISORY https://access.redhat.com/errata/RHSA-2026:3983 ADVISORY https://access.redhat.com/errata/RHSA-2026:3984 ADVISORY https://access.redhat.com/errata/RHSA-2026:4022 ADVISORY https://access.redhat.com/errata/RHSA-2026:4152 ADVISORY https://access.redhat.com/errata/RHSA-2026:4260 ADVISORY https://access.redhat.com/errata/RHSA-2026:4432 ADVISORY https://vuldb.com/vuln/347567 ADVISORY https://www.mozilla.org/security/advisories/mfsa2026-13/ ADVISORY https://www.mozilla.org/security/advisories/mfsa2026-14/ ADVISORY https://www.mozilla.org/security/advisories/mfsa2026-15/ ADVISORY https://www.mozilla.org/security/advisories/mfsa2026-16/ ADVISORY https://www.mozilla.org/security/advisories/mfsa2026-17/ ADVISORY https://www.suse.com/support/update/SUSE-SU-2026:0812/ ADVISORY https://www.suse.com/support/update/SUSE-SU-2026:0871/ ADVISORY https://www.suse.com/support/update/SUSE-SU-2026:0880/ REF https://access.redhat.com/security/cve/CVE-2026-2778 REF https://bugzilla.mozilla.org/show_bug.cgi?id=2016358 REF https://bugzilla.redhat.com/show_bug.cgi?id=2442335 REF https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-2778.json

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