CVE-2026-5734
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Memory Corruption in Firefox and Thunderbird Enables Code Execution

Publication date: 2026-04-07

Last updated on: 2026-04-13

Assigner: Mozilla Corporation

Description
Memory safety bugs present in Firefox ESR 140.9.0, Thunderbird ESR 140.9.0, Firefox 149.0.1 and Thunderbird 149.0.1. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. This vulnerability was fixed in Firefox 149.0.2, Firefox ESR 140.9.1, Thunderbird 149.0.2, and Thunderbird 140.9.1.
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Meta Information
Published
2026-04-07
Last Modified
2026-04-13
Generated
2026-06-16
AI Q&A
2026-04-07
EPSS Evaluated
2026-06-15
NVD
CVE-2026-5734
EUVD
EUVD-2026-19614
Affected Vendors & Products
Showing 4 associated CPEs
Vendor Product Version / Range
mozilla firefox to 149.0.2 (exc)
mozilla firefox to 140.9.1 (exc)
mozilla thunderbird to 149.0.2 (exc)
mozilla thunderbird to 140.9.1 (exc)
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Exploitability
CWE
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KEV
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CWE ID Description
CWE-787 The product writes data past the end, or before the beginning, of the intended buffer.
CWE-120 The product copies an input buffer to an output buffer without verifying that the size of the input buffer is less than the size of the output buffer.
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Executive Summary

This vulnerability involves memory safety bugs found in specific versions of Firefox and Thunderbird, including Firefox ESR 140.9.0, Thunderbird ESR 140.9.0, Firefox 149.0.1, and Thunderbird 149.0.1.

Some of these bugs showed evidence of memory corruption, which means that the software could access or modify memory in unintended ways.

It is presumed that with enough effort, some of these bugs could be exploited by attackers to run arbitrary code on affected systems.

The vulnerability affects Firefox versions earlier than 149.0.2 and Firefox ESR versions earlier than 140.9.1.

Impact Analysis

Exploitation of these memory safety bugs could allow an attacker to execute arbitrary code on your system.

This means that an attacker might be able to take control of your browser or email client, potentially leading to unauthorized access, data theft, or further system compromise.

Mitigation Strategies

To mitigate this vulnerability, update Firefox and Thunderbird to versions that are not affected. Specifically, upgrade Firefox to version 149.0.2 or later, and Firefox ESR to version 140.9.1 or later.

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