When an application uses a custom sanitizer or one of the
bypassSecurityTrust functions, Angular has no way of knowing whether
they are implemented in a secure way. (It doesn't even know if they're
introduced by the application or by a shady third-party dependency.)
Thus using Angular's main Trusted Types policy to bless values coming
from these two sources would undermine the security that Trusted Types
brings.
Instead, introduce a Trusted Types policy called angular#unsafe-bypass
specifically for blessing values from these sources. This allows an
application to enforce Trusted Types even if their application uses a
custom sanitizer or the bypassSecurityTrust functions, knowing that
compromises to either of these two sources may lead to arbitrary script
execution. In the future Angular will provide a way to implement
custom sanitizers in a manner that makes better use of Trusted Types.
PR Close#39218
49197d12a0