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smalex
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Feb 06, 2019

ASM illegal meta character '!'

We are implementing ASM here at the site. We had enabled traffic learning and have got 5000+ suggestions. Majority of those suggestions comes under 'Illegal meta character in URL'. And the illegal character being referred to is the exclamation mark '!'.

 

I understand that I can include that as accepted character, but would like to know why F5 considers '!' as illegal when the RFC declares it to be legal character.

 

Please share your views

 

1 Reply

  • "!" is a dangerous character because in UNIX-based system it can indicate that a text file may become executable (google for "shebang" and "hashbang" if you would like to learn more).

     

    However "!" is also used by some modern frameworks like Angular so I assume that is why you got very high number of learning suggestions to allow it in URLs