CVE-2026-4721
CriticalCVSS 9.8Exploitation Probability (EPSS)
Low risk34th percentile - higher than 34% of all known CVEs
Summary
Memory safety bugs were found in Firefox ESR 115.33, Firefox ESR 140.8, Thunderbird ESR 140.8, Firefox 148, and Thunderbird 148. Some of these bugs showed evidence of memory corruption and could potentially be exploited to run arbitrary code.
Risk Assessment
An attacker could exploit these vulnerabilities to execute arbitrary code remotely on the victim's machine, leading to system compromise, data theft, or malware installation.
Recommendation
Immediately update Firefox and Thunderbird to version 149 (or 115.34/140.9 for ESR versions) and Thunderbird to version 149/140.9.
Original NVD description (English source)
Memory safety bugs present in Firefox ESR 115.33, 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 was fixed in Firefox 149, Firefox ESR 115.34, Firefox ESR 140.9, Thunderbird 149, and Thunderbird 140.9.