Misstep 21: Shim Shimmity

Cabinet with ineffective shimmable lock
Cabinet with Ineffective Lock

You can easily tell how far ahead I am in my security blogs, considering this is scheduled to post in early April and there’s a Christmas Tree ornament hanging from this cabinet, but I digress.

The Misstep

This lock doesn’t even try to fit these knobs, it can easily be moved around to get over them. It is entirely ineffective. Maybe there’s not much of value in here and the deterrent of the lock is good enough? I have no idea what’s inside, but I’ll pretend it is inventory worth more than the lock itself.

This lock has a shackle that engages at several different points. This allows you to winch down onto a locked state at a few different tangs to fit various locking sizes. In this case, the locking size isn’t variable — the knob’s distance won’t vary.

The mechanism here has to have a ratcheting effect to allow you to continue tightening it past the first set point. I’m no artist, but I’m going to share with you some of my art:

Here’s a bit of an oversimplification of how the lock works. There’s a spring that pushes a lock pawl into an angled cut in the shackle. When you lock the padlock, you’ll feel it click as the locking pawl is pushed into the recess in the shackle.

Since this uses an easily collapsible mechanism (the springs) instead of bearings that ride against a locking lug, it is quite easy to interfere with the operation of this lock by using a shim. Shims are easy to make out of pop cans, plastic bottles and other thin, durable materials:

This shim will interfere with the operation of the lock by simply guiding it along the locking lug and slightly compressing the lock. Then, the shim will allow you to slide the shackle open — more than needed to gain access.

The Solution?

In this case, it is probably a shift change issue or something between coworkers where people were using things they shouldn’t have. It was already by a front desk, which tells me the theft/problem was internal. Either train or fire the staff creating an issue, or use a baby-proofing lock to keep folks from entering areas they shouldn’t. This lock is a poor choice -always-. It’s a cheap Master lock four-pin with no security pins, and beyond that — it’s easily shimmable.

And beyond that — it pops right over the darn knobs. None of what I said here matters because of the knobs — it goes right over. The rest here was for the folks using this in a more pragmatic fashion.

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Robert Lerner

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