Can damaged hard drive weaken Mac's security?
The entire question boils down to this:


  How would I know if hard drive is damaged?


Your computer would start to fail - as in crash, errors would be thrown, it would freeze and perform slowly.

When a drive gets damaged, it doesn't suddenly read incorrect data or modified data; the data is corrupted.  Data that can't be read will with cause (at minimum) an error or crash.

Can it weaken security?

Your computer wouldn't be functional by the time it weakened security.  For example, if you are running File Valut, a damaged drive won't decrypt your drive; it won't function. Period.

If you somehow crash your firewall config, SIP (system integrity protection) will throw errors that system files have changed.

So, how do you know if your hard drive is damaged?

If you start getting crashes or freezes or performance problems, one of the things you can do is diagnostic like Apple Hardware Test (AHT).    If you want to just check your disks, there is a nice GUI from Clever Files called DiskDrill (free for the basic utilities, $$ to activate the pro features).  This will help you be proactive.