An attacker could have caused 4 bytes of HMAC output to be written past the end of a buffer stored on the stack. This could be used by an attacker to execute arbitrary code or more likely lead to a crash. This vulnerability affects Firefox < 70, Thunderbird < 68.2, and Firefox ESR < 68.2.
70.0+build2-0ubuntu0.16.04.11:68.7.0+build1-0ubuntu0.16.04.270.0+build2-0ubuntu0.18.04.138.8.0~repack1-0ubuntu138.8.0~repack1-0ubuntu338.8.0~repack1-0ubuntu452.3.1-0ubuntu352.3.1-7fakesync152.8.1-0ubuntu0.18.04.152.9.1-0ubuntu0.18.04.11:68.2.1+build1-0ubuntu0.18.04.170.0+build2-0ubuntu152.9.1-1build152.9.1-1ubuntu3Exploitability
AV:NAC:LPR:NUI:RScope
S:UImpact
C:HI:HA:HCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H