Mozilla Firefox <149 & ESR <140.9 Memory Corruption (Thunderbird)
CVE-2026-4720 Published on March 24, 2026
Memory safety bugs fixed in Firefox ESR 140.9, Thunderbird ESR 140.9, Firefox 149 and Thunderbird 149
Memory safety bugs present in Firefox ESR 140.8, Thunderbird ESR 140.8, Firefox 148 and Thunderbird 148. 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 affects Firefox < 149, Firefox ESR < 140.9, Thunderbird < 149, and Thunderbird < 140.9.
Vulnerability Analysis
CVE-2026-4720 is exploitable with network access, and does not require authorization privileges or user interaction. This vulnerability is considered to have a low attack complexity. The potential impact of an exploit of this vulnerability is considered to be critical as this vulnerability has a high impact to the confidentiality, integrity and availability of this component.
Weakness Type
What is a Classic Buffer Overflow Vulnerability?
The program 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, leading to a buffer overflow. A buffer overflow condition exists when a program attempts to put more data in a buffer than it can hold, or when a program attempts to put data in a memory area outside of the boundaries of a buffer. The simplest type of error, and the most common cause of buffer overflows, is the "classic" case in which the program copies the buffer without restricting how much is copied. Other variants exist, but the existence of a classic overflow strongly suggests that the programmer is not considering even the most basic of security protections.
CVE-2026-4720 has been classified to as a Classic Buffer Overflow vulnerability or weakness.
Products Associated with CVE-2026-4720
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Affected Versions
Mozilla Firefox:- Version unspecified and below 149 is affected.
- Version unspecified and below 140.9 is affected.
- Version unspecified and below 149 is affected.
- Version unspecified and below 140.9 is affected.