W32/Lioten Malicious Code
Release Date: December 17, 2002
Systems running Microsoft Windows 2000 The CERT/CC has received reports of self-propagating malicious code
known as W32/Lioten affecting systems running Windows 2000. This
malicious code exploits weak or null passwords in order to propagate.
Reports to date indicate that thousands of systems are scanning in a
manner consistent with W32/Lioten's known behavior. Various sources
have referred to this malicious code as IraqiWorm and iraqi_oil.exe. W32/Lioten scans for 445/tcp. When it finds a responsive potential
victim, it establishes a null session and retrieves (enumerates) a
list of user accounts on the victim system. For each account it
finds, it then attempts a number of trivial passwords:
Systems Affected
Overview
I. Description
On success, it copies itself to the victim system as iraqi_oil.exe and uses the Task Scheduler (via
at) to run the copy a few minutes later. Presence of the iraqi_oil.exe file
and scanning for 445/tcp are therefore symptoms of compromise.
server
!@#$%^&*
!@#$%^&
!@#$%^
!@#$%
asdfgh
asdf
!@#$
654321
123456
1234
123
111
root
admin
Additional analysis of W32/Lioten can be found at MyNetWatchman.com.
Reports to the CERT/CC indicate that attackers are monitoring for systems infected with W32/Lioten and further exploiting them via other tools for use in distributed denial-of-service (DDoS) attacks.
II. Impact
Systems infected by W32/Lioten scan for 445/tcp. By watching for this scanning activity, attackers are able to easily identify targets with weak passwords and can subsequently compromise those systems for use in other attacks.
Additionally, as with other self-propagating malicious code, W32/Lioten may cause denial-of-service conditions in networks where multiple systems are affected.
III. Solution
Restrict or disable null sessions
Depending on the services your systems are required to provide, it may be possible for you to restrict or disable anonymous null sessions on your Windows 2000 hosts. This can be done through the HKLM\SYSTEM\CurrentControlSet\Control\LSA key with the following parameters:
- Value: RestrictAnonymous
- Value Type: REG_DWORD
- Value Data: 0x1 or 0x2 (Hex)
- 0x0 = None. Rely on default permissions
- 0x1 = Do not allow enumeration of SAM accounts and names
- 0x2 = No access without explicit anonymous permissions
Windows XP sets the RestrictAnonymousSam key to 0x1 by default. Therefore, unless this setting has been altered by the system administrator, W32/Lioten should not be able to retrieve the account list via a null session on Windows XP systems.
Require strong passwords
W32/Lioten exploits the use of weak or null passwords in order to propagate, hence requiring the use of strong passwords can help keep it from infecting your systems.
Ingress/egress filtering
Ingress filtering manages the flow of traffic as it enters a network under your administrative control. In the network usage policy of many sites, external hosts are only permitted to initiate inbound traffic to machines that provide public services on specific ports. Thus, ingress filtering should be performed at the border to prohibit externally initiated inbound traffic to non-authorized services.
Egress filtering manages the flow of traffic as it leaves a network under your administrative control. There is typically limited need for internal systems to access NetBIOS shares across the Internet.
In the case of W32/Lioten, blocking connections to port 445/tcp from entering or leaving your network reduces the risk of external infected systems attacking hosts inside your network or vice-versa.
Author: Allen D. Householder
Copyright 2002 Carnegie Mellon University.