High (7.5). EPSS 2.3% chance of exploitation in the next 30 days.
Same-origin policy protections can be bypassed on pages with embedded iframes during page reloads, allowing the iframes to access content on the top level page, leading to information disclosure. This vulnerability affects Thunderbird < 52.3, Firefox ESR < 52.3, and Firefox < 55.
Severity
CVSS 3.0
7.5 high
CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
EPSS
2.3% chance of exploitation in the next 30 days; higher than 83% of CVEs (scores of 2026-10-31)