ISSalert: ISS Alert: Code Blue Worm

From: X-Force (
Date: 09/10/01

Date: Mon, 10 Sep 2001 12:08:02 -0400
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From: X-Force <>
Subject: ISSalert: ISS Alert: Code Blue Worm

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Internet Security Systems Security Alert
September 10, 2001

Code Blue Worm


ISS X-Force is tracking a new worm found in the wild named "Code Blue".
Testing and analysis of this worm reveals that it is similar in
functionality to the "Code Red" worm, which was released in July 2000.
It is believed that the Code Blue worm will not be as effective as Code
Red, but it still poses a significant threat to unpatched systems.
X-Force has received preliminary reports from a limited number of users
who may have detected Code Blue activity as early as September 6, 2001.


Code Blue is not a memory resident worm like Code Red, which makes Code
Blue easier to detect. It is distributed via a single .DLL (dynamic link
library) and executed by an .EXE file. However, Code Blue is similar to
Code Red in its method of propagation. Once a system is infected, Code
Blue will spawn approximately 100 threads, which will search for
additional systems to infect. Code Blue scans "neighboring" IP
addresses in an effort to reduce scans on un-routable IP networks.
Code Blue will mistakenly scan (loopback) addresses, but it
includes functionality to prevent re-infection of the same system.

Code Blue does not appear to be intentionally destructive or malicious.
It does not delete system files or install backdoor programs on an
infected system. It does, however, greatly affect system stability,
reducing the performance of infected systems. The worm installs a Visual
Basic Script file (d.vbs), which removes ISAPI mappings for ".ida",
".idq", and ".printer" files, and then the worm deletes the script.
Presumably, these mappings are removed to block re-infection by Code Red
or to prevent other attacks using Microsoft IIS ISAPI vulnerabilities.
Each day between the hours of 10am and 11am GMT (6am and 7am EDT), Code
Blue will trigger a packet flooding attack against the IP address of a
Chinese computer security company.

It is unknown how many systems have been compromised by the Code Blue
worm at this time. Code Blue uses the Microsoft IIS Web Server Folder
Traversal vulnerability, which was announced in October 2000. That
vulnerability is described in the following X-Force Security Alert:

Microsoft released patches that eliminate this vulnerability on
August 15, 2000 in response to a previous vulnerability. Microsoft
also included the patch in Windows 2000 Service Pack 2, and in a
Windows NT 4.0 Security Rollup Package (SRP). Due to the widespread
availability of this fix, it is believed that a majority of systems
may have already been patched.

Although Code Blue uses several different attack strings with different
sets of encoded characters, Code Blue scan attempts all follow the same
general format. Code Blue will issue an HTTP HEAD query to a target and
inspect its response. If Code Blue identifies an IIS installation, it
will send an HTTP GET request attempting to exploit the Web Server
Folder Traversal vulnerability. These requests look similar to the

GET /.. [Encoded characters] ../winnt/system32/cmd.exe?/c+dir


ISS RealSecure Network Sensor detects Code Blue scan attempts and will
trigger HTTP_DotDot, HTTP_Head and HTTP_Windows_Executable events. ISS
X-Force recommends that all RealSecure Network Sensor customers closely
examine these events.

ISS RealSecure Server Sensor detects Code Blue scan attempts and will
trigger the following events: Startup_of_important_programs,
Privileged_service_called, and Logon_process_registered.

ISS BlackICE products detect Code Blue scan attempts and will trigger
"2002595 - IIS system32 command" and "2003001 - HTTP port probe" events.

ISS Internet Scanner customers can test for this vulnerability using the
IisUnicodeTranslation check that was included in XPU 4.4 (and later
updated in XPU 4.8).

ISS System Scanner customers can test for this vulnerability using the
MS00-078 check included in XPU 1.13 (#13).

Microsoft IIS administrators who have not yet installed the patch for
the Web Server Folder Traversal vulnerability are encouraged to do so

For Microsoft IIS 4.0:

For Microsoft IIS 5.0:

Administrators may also apply the latest IIS cumulative security patch
(which includes the patch for this vulnerability), available from the
following Microsoft Security Bulletin:

To remove the Code Blue worm from your computer:

1. Using Regedit, find the
   registry key.
2. Find and delete the registry entry for C:\svchost.exe.
3. Delete the file C:\svchost.exe.
4. Delete the file C:\d.vbs, if it remains on your system.
5. Restart your computer.

Additional Information:

Internet Security Systems Security Alert, "Serious flaw in Microsoft IIS
Unicode translation" (describing the Microsoft IIS Web Server Folder
Traversal vulnerability):

Microsoft Security Bulletin MS00-078, "Patch Available for 'Web Server
Folder Traversal' Vulnerability":


About Internet Security Systems (ISS)
Internet Security Systems is a leading global provider of security
management solutions for the Internet, protecting digital assets and
ensuring safe and uninterrupted e-business. With its industry-leading
intrusion detection and vulnerability assessment, remote managed
security services, and strategic consulting and education offerings, ISS
is a trusted security provider to more than 8,000 customers worldwide
including 21 of the 25 largest U.S. commercial banks and the top 10 U.S.
telecommunications companies. Founded in 1994, ISS is headquartered in
Atlanta, GA, with additional offices throughout North America and
international operations in Asia, Australia, Europe, Latin America and
the Middle East. For more information, visit the Internet Security
Systems web site at or call 888-901-7477.

Copyright (c) 2001 Internet Security Systems, Inc.

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