Critical (9.8). EPSS 2.9% chance of exploitation in the next 30 days.
A use-after-free vulnerability can occur in WebSockets when the object holding the connection is freed before the disconnection operation is finished. This results in an exploitable crash. This vulnerability affects Thunderbird < 52.3, Firefox ESR < 52.3, and Firefox < 55.
Severity
CVSS 3.0
9.8 critical
CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
EPSS
2.9% chance of exploitation in the next 30 days; higher than 87% of CVEs (scores of 2026-10-31)