CVE-2025-4919: 
Mozilla Firefox vulnerability analysis and mitigation

CVE-2025-4919 is a critical security vulnerability discovered in Mozilla Firefox that was disclosed on May 17, 2025. The vulnerability affects Firefox versions before 138.0.4, Firefox ESR versions before 128.10.1 and 115.23.1, Thunderbird versions before 128.10.2 and 138.0.2. The flaw allows an attacker to perform an out-of-bounds read or write on a JavaScript object by confusing array index sizes (NVD, Mozilla Advisory).

The vulnerability is classified under CWE-787 (Out-of-bounds Write) and CWE-125 (Out-of-bounds Read). It received a CVSS v3.1 base score of 8.8 (HIGH) with the vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H. The vulnerability specifically occurs during the optimization of linear sums in JavaScript objects, where array index sizes can be manipulated to cause out-of-bounds memory access (NVD, Hacker News).

The vulnerability could allow attackers to perform unauthorized read or write operations on memory, potentially leading to information disclosure or memory corruption. However, Mozilla noted that the attacks did not manage to break out of their sandbox, which is required to gain control over the user's system. Despite this limitation, the vulnerability is still considered critical due to its potential for data exposure and code execution (Hacker News).

Mozilla has released patches for all affected versions. Users are advised to update to Firefox 138.0.4, Firefox ESR 128.10.1, Firefox ESR 115.23.1, Thunderbird 128.10.2, or Thunderbird 138.0.2 as appropriate. Mozilla emphasizes that all users and administrators should update Firefox as soon as possible to mitigate the risk (Hacker News).