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CVE-2026-4371

High

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.

SeverityHigh
CVSS7.4
Exploit probability—
ProductMozilla Thunderbird
PublishedMar 24, 2026
First seenMar 24, 2026
Weakness typeCWE-126CWE-126CWE-130CWE-130

How to fix

Update
  • mozilla thunderbird140.9.0, 149.0 or later
Vendor advisories

Affected products

ProductAffected versionsFixed in
mozilla thunderbirdv < 140.9.0, v < 149.0140.9.0, 149.0

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