How works WebAgent ACO parameter CustomIPHeader

Products

• CA Single Sign On Secure Proxy Server (SiteMinder)
• AXIOMATICS POLICY SERVER
• CA Single Sign On SOA Security Manager (SiteMinder)
• CA Single Sign-On

Issue/Introduction

Question :

I want to know how the ACO parameter customipheader works.
 
I wanted to know the expected behaviour among these 4 configurations
of that parameter :
 
1 - when there's no header
2 - when the header is set with one value;
3 - when the header is set with 2 values;
4 - when the header is set with n > 2 values
 
Answer :
 
By default, the Web Agent obtains the requesting client's IP address
from the Web Server variable REMOTE_ADDR (Remote Address) that the Web
Server sets for a particular request. The Web Agent stores the
client's IP address as value in the SMSESSION cookie.
 
The Web Agent only accept 1 single value is motivated by
security concerns :

CustomIPHeader accepts single value because of security attacks
possible if SiteMinder would allows multiple values :
 
An Example Attack
 
1 - "Alice" logs into SiteMinder with IP 111.111.111.111.
2 - "Mallory" has IP 2.2.2.2.
3 - "Mallory" captures "Alice's" SiteMinder credential and learns her
    IP.
4 - "Mallory" configures his browser to send "Alice's" cookie along
    with the header "x-forwarded-for: 111.111.111.111".
5 - Mallory issues a request to MyHR, ENET, or Authoria.
6 - Proxy modifies the XFF(X-Forwarded-For) header to be
    "111.111.111.111,2.2.2.2".

7 - The Web Agent runs the IP check
8 - The credential contains IP 111.111.111.111
9 - The REMOTE_ADDR is Proxy, so XFF will be used.
10 - The first 15 characters of XFF are 111.111.111.111
11 - IP check passes, because 111.111.111.111 = 111.111.111.111.
12 - Mallory is interactively logged into ACS applications as Alice."

Environment

Release:
Component: SMAPC