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Thunderbird CVE-2026-0881

CRITICAL
Improper Access Control (CWE-284)
2026-01-13 security@mozilla.org
Authentication Bypass Mozilla Thunderbird
10.0
CVSS 3.1 · Vendor: mozilla
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Attack ChainAIDerived

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

  1. Access
    Craft malicious message content
  2. Exploit
    Trigger parsing in Messaging System
  3. Execution
    Escape sandbox isolation
  4. Impact
    Execute arbitrary code with system privileges

Vulnerability Assessment

Weakness
CWE
CWE-284
OWASP Top 10:2025
A01:2025 - Broken Access Control
ASVS 5.0
V8 - Authorization Access control enforcement
MITRE ATT&CK

1 technique across 1 tactic: Defense Evasion

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 Firefox < 147 or Thunderbird < 147 with default Messaging System component enabled.
Impact

CVSS 10.0 (Critical). No auth, network vector, low complexity, scope change. This is a critical sandbox escape – the most valuable type of browser vulnerability. EPSS 0.03%.
Exploit ScenarioDerived

A malicious web page exploits the messaging system vulnerability to escape the browser sandbox, executing arbitrary code on the user's operating system with their full privileges.
Act Now Prioritize within 24-48h. Why: CRITICAL severity.
Patch available 0.0% exploitation probability (EPSS)

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AnalysisAIv1 – Mar 12, 2026

Firefox Messaging System component has a sandbox escape vulnerability. Maximum CVSS 10.0 with scope change. Affects Firefox < 147 and Thunderbird < 147.

Earlier versions of this analysis (1)
v1 Mar 12, 2026 - 21:54 CVSS 10.0

Firefox Messaging System sandbox escape enables code execution on the host OS with maximum severity.

RemediationAI

Update Firefox and Thunderbird immediately. This is a critical security update.

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

A vulnerability in the inter-process messaging system (CWE-284) allows escaping the content process sandbox. The CVSS 10.0 with scope change indicates full host compromise from a web page visit.

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

Vendor (mozilla) 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 Vendor (mozilla).

CVSS VectorVendor: mozilla

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 09, 2026 - 14:30 nvd
Patch available
CVE Published
Jan 13, 2026 - 14:16 nvd
CRITICAL 10.0

DescriptionCVE.org

Sandbox escape in the Messaging System component. This vulnerability affects Firefox < 147 and Thunderbird < 147.

Executive ViewAI

Why It Matters

Organizations using the Messaging System component. This vulnerability affects Firefox face critical risk from CVE-2026-0881, a improper access control vulnerability rated CVSS 10.0. Successful exploitation could critically impact the confidentiality, integrity, and availability of affected systems. Organizations should apply vendor updates immediately when available and implement compensating controls in the interim.

Business Impact: Severe
Compensating Controls

Apply vendor patch. If immediate patching is not feasible: (1) Restrict access to affected endpoints; (2) Implement additional authorization checks; (3) Enable audit logging.

Threat Intelligence Overview

EPSS Score
0.0%
Top 93% 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 0.0%
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

Authentication Bypass CRITICAL

Authentication bypass attacks exploit flaws in the verification mechanisms that control access to systems and applications.

Affected Products (CPE)CVE.org

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

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Same weakness CWE-284 – Improper Access Control

View all
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Same technique Authentication Bypass

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Vendor StatusVendor

SUSE

Severity: High
Product Status
openSUSE Tumbleweed Fixed
SUSE Linux Enterprise Desktop 15 SP7 Fixed
SUSE Linux Enterprise Desktop 15 SP7 Fixed
SUSE Linux Enterprise High Performance Computing 15 SP7 Fixed
SUSE Linux Enterprise Module for Desktop Applications 15 SP7 Fixed

References

Advisories & patches
ADVISORY https://vuldb.com/vuln/340576 ADVISORY https://www.mozilla.org/security/advisories/mfsa2026-01/ ADVISORY https://www.mozilla.org/security/advisories/mfsa2026-04/ REF https://access.redhat.com/security/cve/CVE-2026-0881 REF https://bugzilla.mozilla.org/show_bug.cgi?id=2005845 REF https://bugzilla.redhat.com/show_bug.cgi?id=2428970 REF https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-0881.json

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