CVE-2026-5731
CriticalCVSS 9.8Exploitation Probability (EPSS)
Low risk26th percentile — higher than 26% of all known CVEs
Summary
Memory safety bugs were found in Firefox ESR 115.34.0, 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. The vulnerability was fixed in Firefox 149.0.2, Firefox ESR 115.34.1, Firefox ESR 140.9.1, Thunderbird 149.0.2, and Thunderbird 140.9.1.
Risk Assessment
An attacker could exploit this vulnerability to remotely execute arbitrary code on the victim's system, potentially leading to full system compromise, data theft, or malware installation.
Recommendation
Immediately update all Firefox and Thunderbird instances to the versions specified in the description (Firefox 149.0.2, Firefox ESR 115.34.1/140.9.1, Thunderbird 149.0.2/140.9.1).
Original NVD description (English source)
Memory safety bugs present in Firefox ESR 115.34.0, 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 115.34.1, Firefox ESR 140.9.1, Thunderbird 149.0.2, and Thunderbird 140.9.1.