CVE-2026-5734
CriticalCVSS 9.8Exploitation Probability (EPSS)
Low risk25th percentile — higher than 25% of all known CVEs
Summary
Memory safety bugs were present in Firefox ESR 140.9.0, Thunderbird ESR 140.9.0, Firefox 149.0.1, and Thunderbird 149.0.1. 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 on the victim's system, leading to full compromise of the browser or mail client and potentially the entire system.
Recommendation
Immediately update Firefox to version 149.0.2, Firefox ESR to 140.9.1, Thunderbird to 149.0.2, and Thunderbird ESR to 140.9.1.
Original NVD description (English source)
Memory safety bugs present in Firefox ESR 140.9.0, Thunderbird ESR 140.9.0, Firefox 149.0.1 and Thunderbird 149.0.1. 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 149.0.2, Firefox ESR 140.9.1, Thunderbird 149.0.2, and Thunderbird 140.9.1.