A flaw in the Widget: Win32 component allows a malicious page to bypass the browser sandbox by exploiting incorrect boundary checks. This is an instance of buffer overrun and improper input validation (CWE-119), unchecked input bounds (CWE-20), unsafe code path selection (CWE-653), and insecure code path selection (CWE-693). The bug can lead to execution with higher privileges than the sandbox grants, potentially compromising the confidentiality, integrity, and availability of the host system. The vulnerability carries a CVSS score of 9.6. The vulnerability has been fixed in Firefox 151, Firefox ESR 140.11, Thunderbird 151, and Thunderbird 140.11.

Mozilla Firefox, all builds prior to Firefox 151 and Firefox ESR 140.11, and Mozilla Thunderbird, all builds prior to Thunderbird 151 and Thunderbird 140.11, were affected. The security update was released for Firefox 151, Firefox ESR 140.11, Thunderbird 151, and Thunderbird 140.11 and later versions.

The vulnerability has a CVSS score of 9.6, indicating critical severity. EPSS score is 0.00083, indicating a very low exploitation probability. The vulnerability is not listed in the CISA KEV catalog. The likely attack vector is remote, originating from a malicious web page or content delivered through the affected component. The risk is elevated due to the potential for sandbox escape, but the exploitation probability remains very low.