If you’re familiar with under-door tools from Nathan Anderson’s Physical Entry Bypass post in this series, you know they’re incredibly effective for accessing lever handles on the other side of a door in order to gain entry. However, even the best tools can benefit from simple modifications. Today, I want to share a game-changing improvement that will significantly enhance your under-door tool’s effectiveness for your physical social engineering engagements.
The Problem
As always, I want to start by stating that this technique is very useful for security engagements. Using any of these tips without a clearly scoped contract is illegal, and Raxis does not condone such activities. Let’s all stay ethical!
One of the most common issues with standard under-door tools is the lack of grip when engaging door handles. This is especially problematic with those sweep-back handles (often called California returns due to fire code requirements) or European-style door handles. When your tool slips off the handle during a critical moment, it can be frustrating and time-consuming.
The Simple Solution: Adding Grip
The head of your under-door tool—the part that guides the string behind the door handle and eventually pulls down on it—can be significantly improved with a simple modification: adding a grippy surface.
In a past Raxis Red Team engagement that I was a part of, we were fighting a handle on the server room door. After working for about 20 minutes on the door, we took the top of the tool that sits on the handle and wrapped it with a couple of wraps of gaffer’s tape. Next we turned the gaffer’s tape sticky side out and rolled it around the corner of the tool – securing it again with a couple of small wraps of tape on both sides.
Gaffer’s tape is nice because it’s designed to have strong grip but not leave a sticky residue like duct tape or other similar tapes. Everyone has gaffers’ tape in your kit, right?
After this quick field mod, the tool literally stuck to the door handle. Two tries and a few seconds later we successfully manipulated the door handle and found ourselves inside the server room.
Another Option: Heat-Shrink Tubing
While we used tape because it’s what we had on hand, heat-shrink tubing offers a cleaner, more professional solution. Here’s how to apply it:
- Cut a piece of heat-shrink tubing to length (non-marine heat-shrink without adhesive inside is preferred)
- Slide it up the handle and around the top section
- Apply heat to shrink it into place
You don’t need to wrap the entire tool—just focus on the critical contact area at the top. Once applied, the heat-shrink provides that crucial bit of friction that prevents slipping, allowing you to pull harder on those handles when needed.
Why This Modification Matters
This simple addition transforms your tool’s performance by:
- Increasing the friction between the tool and door handle
- Preventing slippage during critical moments
- Allowing for more consistent engagement with various handle types
- Not leaving behind any residue or damage
The beauty of this modification is its simplicity. It requires minimal materials, takes just minutes to implement, and dramatically improves functionality.
Interested in reading more about our physical social engineering exploits? Watch for the next post in our PSE & Red Team Series.
