CVE-2026-5731
Modified Modified - Updated After Analysis

Memory Corruption in Firefox and Thunderbird Enables Code Execution

Publication date: 2026-04-07

Last updated on: 2026-06-30

Assigner: Mozilla Corporation

Description
Memory safety bugs present in Firefox ESR 115.34.0, 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 115.34.1, 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
2026-06-30
Generated
2026-07-06
AI Q&A
2026-04-07
EPSS Evaluated
2026-07-05
NVD
CVE-2026-5731
EUVD
EUVD-2026-19610

Affected Vendors & Products

Showing 5 associated CPEs
Vendor Product Version / Range
mozilla firefox 140.9.0
mozilla firefox 149.0.1
mozilla thunderbird 140.9.0
mozilla thunderbird 149.0.1
mozilla firefox 115.34.0

Helpful Resources

Exploitability

CWE
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KEV
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CWE ID Description
CWE-119 The product performs operations on a memory buffer, but it reads from or writes to a memory location outside the buffer's intended boundary. This may result in read or write operations on unexpected memory locations that could be linked to other variables, data structures, or internal program data.
CWE-787 The product writes data past the end, or before the beginning, of the intended buffer.

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Compliance Impact

The provided information does not specify how CVE-2026-5731 affects compliance with common standards and regulations such as GDPR or HIPAA.

Executive Summary

CVE-2026-5731 involves multiple memory safety vulnerabilities found in specific versions of Firefox ESR, Firefox, and Thunderbird. These vulnerabilities are memory corruption bugs that could potentially be exploited to execute arbitrary code on affected systems.

Impact Analysis

The impact of this vulnerability is considered high because successful exploitation could allow an attacker to run arbitrary code. This means an attacker could potentially take control of your system or application by exploiting these memory safety bugs.

Mitigation Strategies

To mitigate this vulnerability, you should update affected software to the fixed versions released by Mozilla.

  • Upgrade Firefox ESR to version 115.34.1 or later.
  • Upgrade Firefox ESR to version 140.9.1 or later.
  • Upgrade Thunderbird ESR to version 140.9.1 or later.
  • Upgrade Firefox to version 149.0.2 or later.
  • Upgrade Thunderbird to version 149.0.2 or later.

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