CVE-2025-4919

An attacker was able to perform an out-of-bounds read or write on a JavaScript object by confusing array index sizes. This vulnerability affects Firefox < 138.0.4, Firefox ESR < 128.10.1, Firefox ESR < 115.23.1, Thunderbird < 128.10.2, and Thunderbird < 138.0.2.

A flaw was found in Firefox and Thunderbird. The Mozilla Foundation's Security Advisory describes the following issue: An attacker could perform an out-of-bounds read or write on a JavaScript object by confusing array index sizes.

This vulnerability allows remote attackers to execute arbitrary code on affected installations of Mozilla Firefox. User interaction is required to exploit this vulnerability in that the target must visit a malicious page or open a malicious file.
The specific flaw exists within the SpiderMonkey engine. The issue results from the lack of proper validation of user-supplied data, which can result in a write past the end of an allocated buffer. An attacker can leverage this vulnerability to execute code in the context of the current process.

Multiple security issues were discovered in Thunderbird, which could result in the execution of arbitrary code. For the stable distribution (bookworm), these problems have been fixed in version 1:128.11.0esr-1~deb12u1.