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Problem this snippet solves:

Do you know how to prevent horizontal privilege escalation using F5?


that's what we already did for one of our customers, F5 WAF can protect the web application from unauthenticated attacks or even vertical privilege escalation, but by default, we couldn't find a way to prevent the attacker from accessing pages that he doesn't have access to after login.

and here we decided to use iRule!

depending on a sessionID (Random Dynamic Value) cookie and another unencrypted cookie that defines the user role (Static Value) we made it!

the web application now can validate if the user is allowed to access the page or not before giving him access.

that was awesome for me and that's why I love F5 🙂


How to use this snippet:


Code :

when CLIENT_ACCEPTED {
# Global Variables
  set cookiename "F5_Role_Cookie"
  set encryption_passphrase "Encryption Key, that should be long and complex"
}


when HTTP_RESPONSE {
	if { $uri equals "/" } {
		set uRole [HTTP::cookie "DEV-Cookie"]  
		#log local0. "LogIdentifier uRole: $uRole"
		set roleCookie $uRole
		append roleCookie #sessionID and also part of string
		#log local0. "LogIdentifier uRole: $uRole"
		#log local0. "LogIdentifier uRole: $roleCookie"

		HTTP::cookie remove "DEV-Cookie"
		HTTP::cookie insert name "F5_Role_Cookie" value $roleCookie path "/"
		HTTP::cookie encrypt $cookiename $encryption_passphrase
		log local0. "LogIdentifier EncryptedCookie: [HTTP::cookie "F5_Role_Cookie"]"
	}
}

	switch [HTML::tag name] {
		"form" {
	if { [HTML::tag attribute "action"] equals "./home.aspx" } {
	HTML::tag attribute replace "action" "./"
}
}
}
}


when HTTP_REQUEST {
	#lowercase URI to avoid case sensitive manipulation
	set uri [string tolower [HTTP::uri]] 
	set sessionID [HTTP::cookie "ASP.NET_SessionId"]
	#log local0. "LogIdentifier sessionID: $sessionID"
	#decrypt the cookie
	set decrypted [HTTP::cookie decrypt $cookiename $encryption_passphrase]
	log local0. "Log1 LogIdentifier DecryptedCookie: $decrypted"
	log local0. "Log2 LogIdentifier URI is: $uri"
	if { [matchclass $uri equals URI-List-AnyAccess] } {
		log local0. "Log3 LogIdentifier class AnyAccess $uri"
		return
	} elseif { $uri starts_with "/font" } {
		log local0. "Log3 LogIdentifier Font $uri "
		return
	} elseif { $uri contains "/scripts/" } {
		log local0. "Log3 LogIdentifier Font $uri "
		return
	} elseif { $uri contains "/images/" } {
		log local0. "Log3 LogIdentifier Images $uri "
		return
	} elseif { $uri contains "/css/" } {
		log local0. "Log3 LogIdentifier class CSS $uri "
		return
	} elseif { ( [matchclass $uri equals URI-Role1] ) && #condition to compare session ID and Role1 } {
		return	
	} elseif { ( [matchclass $uri equals URI-Role2] ) && #condition to compare session ID and Role2 } {
		return
	} elseif { ( [matchclass $uri equals URI-Role3] ) && #condition to compare session ID and Role3 } {
		return
	} elseif { ( [matchclass $uri equals URI-Role4] ) && #condition to compare session ID and Role4 } {
		return

	} elseif { ( [matchclass $uri equals URI-Role5] ) && #condition to compare session ID and Role5 } {
		return	
	} elseif { ( [matchclass $uri equals URI-Role6] ) && #condition to compare session ID and Role6 } {
		return
	} elseif { ( [matchclass $uri equals URI-Role7] ) && #condition to compare session ID and Role7 } {
		return
	} elseif { ( [matchclass $uri equals URI-Role8] ) && #condition to compare session ID and Role8 } {
		return
	} else {
  		log local0. "Log3 LogIdentifier 403 AccessDenied $uri "
		HTTP::redirect "https://site.com/accessdenied"
	}
}

Tested this on version:

13.0
Version history
Last update:
‎21-Oct-2020 02:26
Updated by:
Contributors