Year ago, in February 2018, I was testing Facebook Messenger for Android looking how it works with corrupted GIF images. I was inspired by Imagemagick "uninitialized memory disclosure in gif coder" bug and PoC called "gifoeb" (cool name for russian speakers). I found Messenger app only crashes with images generated by "gifoeb" tool with Nullpointer dereferrence (Facebook did't awarded bounty for DoS in Facebook Messenger for Android).
Ok. I thought: what is GIF image format and how it looks, how I can generate my own image?
(spoiler: 10K$ bug in Facebook Messenger for Web, but theory first)
Internationalized domain name (IDN) homograph attack is way a thirdparty may confuse users exploiting the fact that many characters may look alike. For example urls "https://bank.com" and "https://bаnk.com" are look as the same, but actually first url contains latin "a", the second cyrilic "а" which looks alike latin. This characters are called "homoglyphs". You may find more homoglyphs at http://www.irongeek.com/homoglyph-attack-generator.php .
IDN can be represented as unicode url or punycode.
Basically you can't register domain names with homoglyphs. Try to register "bаnk.com" and request will be rejected, because this name contains cyrilic "а". IDN registration policy not allow to mix latin and cyrilic letters. More details about restrictions you can find here and at iana.org.
In IDN latin table (which represent permitted code points (letters) allowed for Internationalised Domain Name registrations) exis…