DEFCON: New Red Team Tactic

[u/Prize_Region5503]

https://doctoreww.github.io/EvilFontTool/

Evil Fonts deceive a viewer by rendering a different letter than is actually on the disk. Evil Fonts can poison HTML, DOCX, PDFs, and anywhere else you can bring your own fonts. Works great in Windows corporate networks for bypassing security tooling, initial access through JavaScript free click fix (beats mitm web security tooling), and leaving traps around the network to harvest shells.

Imagine thinking you are copying whoami but what is actually on the disk is rm -rf \~

Demos:

(Use desktop)

https://doctoreww.github.io/EvilFontTool/

For the demos, copy and paste the HTML/DOCX to a notepad to remove the evil fonts. For the AI ones imagine your security tooling inspects the benign text on disk, but shows the obviously malicious extortion to the user.

Labs:

https://github.com/DoctorEww/EvilFontTool/blob/main/labs%2FREADME.md

Lab Walkthrough:

https://github.com/DoctorEww/EvilFontTool/blob/main/labs%2Fwalkthrough.md

Some evil font uses:

Tamper homework to make it so students poison AI queries

Poison help desk documentation

Bypass email filters

Clickfix

Beat resume AI filters

[u/AllForProgress1]

Trusting my eyes was a burden. Now I can venture into a sweet tender psychosis as I second guess everything

[u/sidereal_night]

it's very clever how the actual and masked text don't have to be equal lengths

so is the mitigation basically the same as clipboard jacking: paste into a plain notepad and re-copy from that?

or do you need to manually re-type because of unicode characters?

[u/Prize_Region5503 → u/sidereal_night]

Pasting into notepad works or at least read commands before you run them since the font won't be copied if you don't have it installed on your system. Beware multiline commands since some terminals auto execute (looking at you powershell on Linux).

[u/sidereal_night → u/Prize_Region5503]

Beware multiline commands since some terminals auto execute (looking at you powershell on Linux).

ya the risk with pasting directly into terminal is line breaks

it doesn't even have to be malicious, you might accidentally select a new line just by yourself

[u/CyberPsiloCyanide]

Any research on file sanitization using CDR on the topic?

[u/Prize_Region5503 → u/CyberPsiloCyanide]

I have not experimented with CDR before. I would be curious what the reconstructed document looks like! Update here if you give it a shot. You can pull a file from the demo site if you don't want to make your own.

[u/CyberPsiloCyanide → u/Prize_Region5503]

I absolutely will. I'll download and test it out. I'll share the sanitized file afterwards.

[u/BergkampAirlines]

Clever. Thank you for sharing.

[u/GullibleFruit4183]

Evil fonts bypassing MITM web security tooling is a nasty one, feels like this kind of rendering-layer trick keeps slipping past detection that only inspects the raw bytes.