>>> CVE-2020-12387: Use-after-free during worker shutdown
>>> Impact: critical
>>> A race condition when running shutdown code for Web Worker led to a use-after-free vulnerability. This resulted in a potentially exploitable crash.
And:
>>> CVE-2020-12388: Sandbox escape with improperly guarded Access Tokens
>>> Impact: critical
>>> The Firefox content processes did not sufficiently lockdown access control which could result in a sandbox escape. [On Windows]
So a sandbox escape and a way to be in a position to need a sandbox escape.
>>> CVE-2020-12387: Use-after-free during worker shutdown
>>> Impact: critical
>>> A race condition when running shutdown code for Web Worker led to a use-after-free vulnerability. This resulted in a potentially exploitable crash.
And:
>>> CVE-2020-12388: Sandbox escape with improperly guarded Access Tokens
>>> Impact: critical
>>> The Firefox content processes did not sufficiently lockdown access control which could result in a sandbox escape. [On Windows]
So a sandbox escape and a way to be in a position to need a sandbox escape.