Forum Discussion

smalex's avatar
smalex
Icon for Altostratus rankAltostratus
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

 

application delivery
ASM Advanced WAF
security
  • samstep's avatar
    samstep
    Icon for Cirrocumulus rankCirrocumulus
    Feb 11, 2019

    "!" 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