An integer overflow fault caused by incorrect boundary checks in the XPCOM component can allow a sandbox escape. The flaw permits an attacker to feed crafted data that overflows a signed integer, enabling a boundary failure and ultimately breaking out of the hardened execution context. The escape can provide the attacker with the ability to execute arbitrary code that runs with the permissions of the compromised application, thereby threatening confidentiality, integrity, and availability of the entire system.

Mozilla Firefox versions earlier than 149, including the ESR 115.34 and ESR 140.9 releases, and Mozilla Thunderbird versions earlier than 149, including the ESR 140.9 release, are affected.

The vulnerability has a CVSS v3 score of 10 and an EPSS probability of less than 1 %. It is not listed in the CISA KEV catalog. The likely attack vector involves an attacker interacting with the affected software to supply malicious data that triggers the integer overflow, which can lead to a system‑wide compromise once the sandbox is escaped.