Critical (9.8). EPSS 3.0% chance of exploitation in the next 30 days.
An out-of-bounds read when an HTTP/2 connection to a servers sends "DATA" frames with incorrect data content. This leads to a potentially exploitable crash. This vulnerability affects Thunderbird < 52.1, Firefox ESR < 45.9, Firefox ESR < 52.1, and Firefox < 53.
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
3.0% chance of exploitation in the next 30 days; higher than 87% of CVEs (scores of 2026-10-31)