High (8.4). EPSS 0.4% chance of exploitation in the next 30 days.
`AppendEncodedAttributeValue(), ExtraSpaceNeededForAttrEncoding()` and `AppendEncodedCharacters()` could have experienced integer overflows, causing underallocation of an output buffer leading to an out of bounds write. This vulnerability affects Firefox < 124, Firefox ESR < 115.9, and Thunderbird < 115.9.
Severity
CVSS 3.1
8.4 high
CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
EPSS
0.4% chance of exploitation in the next 30 days; higher than 32% of CVEs (scores of 2026-10-31)