Is CVE-2026-4371 in the CISA KEV catalog?

No. CVE-2026-4371 is not currently on the CISA Known Exploited Vulnerabilities list.

What is the CVSS severity of CVE-2026-4371?

CVE-2026-4371 has a CVSS v3 base score of 7.4 (HIGH).

What is the EPSS score for CVE-2026-4371?

CVE-2026-4371 has an EPSS score of 0.36% (28th percentile), estimating the probability of exploitation in the next 30 days.

How do I fix CVE-2026-4371?

Upgrade thunderbird on debian 11 to 1:140.9.0esr-1~deb11u1 or later. Fixes are available for 8 affected products.

CVE & CISA-KEV Catalog

CVE-2026-4371

HIGH

7.4

CVSS v3

NVD

Description

A malicious mail server could send malformed strings with negative lengths, causing the parser to read memory outside the buffer. If a mail server or connection to a mail server were compromised, an attacker could cause the parser to malfunction, potentially crashing Thunderbird or leaking sensitive data. This vulnerability was fixed in Thunderbird 149 and Thunderbird 140.9.

CWE-126Buffer Over-read CWE-130

How to fix

Remediation Available

thunderbirdDebian

Fixed in:1:140.9.0esr-1~deb11u1CVE-2026-4371

Fixed in:1:140.9.0esr-1~deb12u1CVE-2026-4371

Fixed in:1:140.9.0esr-1~deb13u1CVE-2026-4371

Fixed in:1:140.9.0esr-1CVE-2026-4371

thunderbirdRocky

Fixed in:0:140.9.0-1.el10_1RHSA-2026:6342

Fixed in:0:140.9.0-1.el10_0RHSA-2026:8315

Fixed in:0:140.9.0-1.el10_1RHSA-2026:6342

Fixed in:0:140.9.0-1.el10_0RHSA-2026:8315

Fixed in:0:140.9.0-1.el10_1RHSA-2026:6342

Fixed in:0:140.9.0-1.el8_2RHSA-2026:8285

Fixed in:0:140.9.0-1.el8_10RHSA-2026:6917

Fixed in:0:140.9.0-1.el8_6RHSA-2026:8289

Fixed in:0:140.9.0-1.el8_4RHSA-2026:8850

Fixed in:0:140.9.0-1.el8_6RHSA-2026:8289

Fixed in:0:140.9.0-1.el8_4RHSA-2026:8850

Fixed in:0:140.9.0-1.el8_8RHSA-2026:8288

Fixed in:0:140.9.0-1.el8_2RHSA-2026:8285

Fixed in:0:140.9.0-1.el9_4RHSA-2026:8290

Fixed in:0:140.9.0-1.el9_2RHSA-2026:8287

Fixed in:0:140.9.0-1.el9_7RHSA-2026:6188

Fixed in:0:140.9.0-1.el9_0RHSA-2026:8286

Fixed in:0:140.9.0-1.el9_2RHSA-2026:8287

Fixed in:0:140.9.0-1.el9_7RHSA-2026:6188

Fixed in:0:140.9.0-1.el9_4RHSA-2026:8290

Fixed in:0:140.9.0-1.el9_0RHSA-2026:8286

Fixed in:0:140.9.0-1.el9_4RHSA-2026:8290

Fixed in:0:140.9.0-1.el9_2RHSA-2026:8287

Fixed in:0:140.9.0-1.el9_6RHSA-2026:8284

Fixed in:0:140.9.0-1.el9_2RHSA-2026:8287

Fixed in:0:140.9.0-1.el9_6RHSA-2026:8284

Fixed in:0:140.9.0-1.el9_2RHSA-2026:8287

Fixed in:0:140.9.0-1.el9_0RHSA-2026:8286

Fixed in:0:140.9.0-1.el9_4RHSA-2026:8290

Fixed in:0:140.9.0-1.el9_0RHSA-2026:8286

Fixed in:0:140.9.0-1.el9_4RHSA-2026:8290

thunderbirdRed Hat / RHEL

Fixed in:0:140.9.0-1.el10_0RHSA-2026:8315

Fixed in:0:140.9.0-1.el10_1RHSA-2026:6342

Fixed in:0:140.9.0-1.el10_0RHSA-2026:8315

Fixed in:0:140.9.0-1.el8_10RHSA-2026:6917

Fixed in:0:140.9.0-1.el8_2RHSA-2026:8285

Fixed in:0:140.9.0-1.el8_6RHSA-2026:8289

Fixed in:0:140.9.0-1.el8_4RHSA-2026:8850

Fixed in:0:140.9.0-1.el8_8RHSA-2026:8288

Fixed in:0:140.9.0-1.el8_4RHSA-2026:8850

Fixed in:0:140.9.0-1.el8_10RHSA-2026:6917

Fixed in:0:140.9.0-1.el9_7RHSA-2026:6188

Fixed in:0:140.9.0-1.el9_0RHSA-2026:8286

Fixed in:0:140.9.0-1.el9_7RHSA-2026:6188

Fixed in:0:140.9.0-1.el9_6RHSA-2026:8284

Fixed in:0:140.9.0-1.el9_7RHSA-2026:6188

Fixed in:0:140.9.0-1.el9_0RHSA-2026:8286

Fixed in:0:140.9.0-1.el9_7RHSA-2026:6188

Fixed in:0:140.9.0-1.el9_2RHSA-2026:8287

Fixed in:0:140.9.0-1.el9_6RHSA-2026:8284

Fixed in:0:140.9.0-1.el9_4RHSA-2026:8290

Fixed in:0:140.9.0-1.el9_2RHSA-2026:8287

Fixed in:0:140.9.0-1.el9_6RHSA-2026:8284

Fixed in:0:140.9.0-1.el9_4RHSA-2026:8290

Fixed in:0:140.9.0-1.el9_2RHSA-2026:8287

Fixed in:0:140.9.0-1.el9_4RHSA-2026:8290

Fixed in:0:140.9.0-1.el9_6RHSA-2026:8284

Fixed in:0:140.9.0-1.el9_0RHSA-2026:8286

Fixed in:0:140.9.0-1.el9_2RHSA-2026:8287

Fixed in:0:140.9.0-1.el9_0RHSA-2026:8286

Fixed in:0:140.9.0-1.el9_6RHSA-2026:8284

thunderbird-debuginfoRocky

Fixed in:0:140.9.0-1.el10_0RHSA-2026:8315

Fixed in:0:140.9.0-1.el10_1RHSA-2026:6342

Fixed in:0:140.9.0-1.el10_0RHSA-2026:8315

Fixed in:0:140.9.0-1.el10_1RHSA-2026:6342

Fixed in:0:140.9.0-1.el10_0RHSA-2026:8315

Fixed in:0:140.9.0-1.el10_1RHSA-2026:6342

Fixed in:0:140.9.0-1.el8_8RHSA-2026:8288

Fixed in:0:140.9.0-1.el8_10RHSA-2026:6917

Fixed in:0:140.9.0-1.el8_2RHSA-2026:8285

Fixed in:0:140.9.0-1.el8_10RHSA-2026:6917

Fixed in:0:140.9.0-1.el8_8RHSA-2026:8288

Fixed in:0:140.9.0-1.el8_6RHSA-2026:8289

Fixed in:0:140.9.0-1.el8_10RHSA-2026:6917

Fixed in:0:140.9.0-1.el8_6RHSA-2026:8289

Fixed in:0:140.9.0-1.el8_4RHSA-2026:8850

Fixed in:0:140.9.0-1.el8_10RHSA-2026:6917

Fixed in:0:140.9.0-1.el8_6RHSA-2026:8289

Fixed in:0:140.9.0-1.el9_7RHSA-2026:6188

Fixed in:0:140.9.0-1.el9_2RHSA-2026:8287

Fixed in:0:140.9.0-1.el9_6RHSA-2026:8284

Fixed in:0:140.9.0-1.el9_7RHSA-2026:6188

Fixed in:0:140.9.0-1.el9_4RHSA-2026:8290

Fixed in:0:140.9.0-1.el9_0RHSA-2026:8286

thunderbird-debuginfoRed Hat / RHEL

Fixed in:0:140.9.0-1.el10_0RHSA-2026:8315

Fixed in:0:140.9.0-1.el10_1RHSA-2026:6342

Fixed in:0:140.9.0-1.el10_0RHSA-2026:8315

Fixed in:0:140.9.0-1.el10_1RHSA-2026:6342

Fixed in:0:140.9.0-1.el10_0RHSA-2026:8315

Fixed in:0:140.9.0-1.el8_4RHSA-2026:8850

Fixed in:0:140.9.0-1.el8_6RHSA-2026:8289

Fixed in:0:140.9.0-1.el8_2RHSA-2026:8285

Fixed in:0:140.9.0-1.el8_10RHSA-2026:6917

Fixed in:0:140.9.0-1.el8_6RHSA-2026:8289

Fixed in:0:140.9.0-1.el8_10RHSA-2026:6917

Fixed in:0:140.9.0-1.el8_6RHSA-2026:8289

Fixed in:0:140.9.0-1.el8_10RHSA-2026:6917

Fixed in:0:140.9.0-1.el8_6RHSA-2026:8289

Fixed in:0:140.9.0-1.el8_8RHSA-2026:8288

Fixed in:0:140.9.0-1.el8_10RHSA-2026:6917

Fixed in:0:140.9.0-1.el8_8RHSA-2026:8288

Fixed in:0:140.9.0-1.el9_2RHSA-2026:8287

Fixed in:0:140.9.0-1.el9_6RHSA-2026:8284

Fixed in:0:140.9.0-1.el9_7RHSA-2026:6188

Fixed in:0:140.9.0-1.el9_4RHSA-2026:8290

Fixed in:0:140.9.0-1.el9_0RHSA-2026:8286

thunderbird-debugsourceRocky

Fixed in:0:140.9.0-1.el10_1RHSA-2026:6342

Fixed in:0:140.9.0-1.el10_0RHSA-2026:8315

Fixed in:0:140.9.0-1.el10_1RHSA-2026:6342

Fixed in:0:140.9.0-1.el8_6RHSA-2026:8289

Fixed in:0:140.9.0-1.el8_10RHSA-2026:6917

Fixed in:0:140.9.0-1.el8_2RHSA-2026:8285

Fixed in:0:140.9.0-1.el8_8RHSA-2026:8288

Fixed in:0:140.9.0-1.el8_6RHSA-2026:8289

Fixed in:0:140.9.0-1.el8_4RHSA-2026:8850

Fixed in:0:140.9.0-1.el9_7RHSA-2026:6188

Fixed in:0:140.9.0-1.el9_4RHSA-2026:8290

Fixed in:0:140.9.0-1.el9_2RHSA-2026:8287

Fixed in:0:140.9.0-1.el9_4RHSA-2026:8290

Fixed in:0:140.9.0-1.el9_7RHSA-2026:6188

Fixed in:0:140.9.0-1.el9_4RHSA-2026:8290

Fixed in:0:140.9.0-1.el9_7RHSA-2026:6188

Fixed in:0:140.9.0-1.el9_4RHSA-2026:8290

Fixed in:0:140.9.0-1.el9_0RHSA-2026:8286

Fixed in:0:140.9.0-1.el9_6RHSA-2026:8284

Fixed in:0:140.9.0-1.el9_2RHSA-2026:8287

thunderbird-debugsourceRed Hat / RHEL

Fixed in:0:140.9.0-1.el10_1RHSA-2026:6342

Fixed in:0:140.9.0-1.el10_0RHSA-2026:8315

Fixed in:0:140.9.0-1.el10_1RHSA-2026:6342

Fixed in:0:140.9.0-1.el8_10RHSA-2026:6917

Fixed in:0:140.9.0-1.el8_2RHSA-2026:8285

Fixed in:0:140.9.0-1.el8_10RHSA-2026:6917

Fixed in:0:140.9.0-1.el8_8RHSA-2026:8288

Fixed in:0:140.9.0-1.el8_6RHSA-2026:8289

Fixed in:0:140.9.0-1.el8_4RHSA-2026:8850

Fixed in:0:140.9.0-1.el9_7RHSA-2026:6188

Fixed in:0:140.9.0-1.el9_2RHSA-2026:8287

Fixed in:0:140.9.0-1.el9_0RHSA-2026:8286

Fixed in:0:140.9.0-1.el9_6RHSA-2026:8284

Fixed in:0:140.9.0-1.el9_0RHSA-2026:8286

Fixed in:0:140.9.0-1.el9_6RHSA-2026:8284

Fixed in:0:140.9.0-1.el9_4RHSA-2026:8290

Fixed in:0:140.9.0-1.el9_0RHSA-2026:8286

Fixed in:0:140.9.0-1.el9_4RHSA-2026:8290

Mozilla Thunderbird (en-US)Windows application

Affected:149.0Fixed in:149.0Mozilla

Affected:140.9.0Fixed in:140.9.0Mozilla

TridentStack Control can deploy fixes like this automatically across your Windows, macOS, and Linux fleet. See how it works

Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.

CVSS v3 Vector

Exploitability

Attack VectorNetwork

Attack ComplexityHigh

Privileges RequiredNone

User InteractionNone

ScopeUnchanged

Impact

ConfidentialityHigh

IntegrityNone

AvailabilityHigh

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:H

Exploit Intelligence

0.36%probability of exploitation in 30 days

28thpercentile

Low risk: more likely to be exploited than 28% of all known CVEs.

References

Vendor Advisory2

Other references16

Related Vulnerabilities

Other CWE-126 (Buffer Over-read) vulnerabilities, ordered by exploit likelihood. View all

CVE	Severity	CVSS	EPSS	Exploited	Fix
CVE-2023-49285	High	8.6	89%	-	Fix
CVE-2017-7668	High	7.5	57%	-	Fix
CVE-2017-7679	Critical	9.8	39%	-	Fix
CVE-2025-21277	High	7.5	38%	-	Fix
CVE-2024-38071	High	7.5	36%	-	Fix
CVE-2009-2495	Medium	6.5	34%	-	-

Embed a live status badge for CVE-2026-4371

Markdown

[![CVE-2026-4371](https://tridentstack.com/cve/badge/CVE-2026-4371.svg)](https://tridentstack.com/cve/CVE-2026-4371)

HTML

<a href="https://tridentstack.com/cve/CVE-2026-4371"><img src="https://tridentstack.com/cve/badge/CVE-2026-4371.svg" alt="CVE-2026-4371"></a>

Find and fix vulnerabilities across your fleet

TridentStack Control continuously scans your Windows, macOS, and Linux fleet for known vulnerabilities, prioritizes them by severity and active exploitation, and patches them automatically.

See how it works Start freeThis CVE lookup is free and always will be.

This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-07-15.