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Anthony_Epron's avatar
Anthony_Epron
Icon for Nimbostratus rankNimbostratus
Jun 16, 2020

Irule to make HTTP request size compliant with header

Hello,

 

I need to implement in F5 is a possibility to reject an HTTP request in case the size of the request is not corresponding to the Content-Length of the header.

 

I cannot use ASM for it.

 

I think use an irule like below where I can find a way to replace "set req [HTTP::request]" by a condition who indicate the size of the request in bit.

 

when HTTP_REQUEST {

  set req [HTTP::request]

   set len [HTTP::header "Content-Length"]

     if { [expr $len eq ne expr $lreq} {

       reject

     }

   }

 }

 

Thanks in advance for your help.

iRules
LTM
security
  • PeteWhite's avatar
    PeteWhite
    Icon for Employee rankEmployee
    Jun 21, 2020

    what you are trying to do will work with GET but you may wish to consider POST, where you will have to use HTTP::collect and use HTTP::payload length.

    For use with GET, you can simply use string length:

    when HTTP_REQUEST {
  if { [expr {  [string length [HTTP::request]] eq ne expr [HTTP::header "Content-Length"]} {
    reject
  }
 }