[CH] to my PC friends from MAC Head Durkee
Shantihhh@aol.com
Fri, 18 Dec 1998 12:26:14 EST
Subject: [gardeners] OT: HO HO HO virus
Just received this from one of our technical architects.
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The lovely christmas greetings from the 'net via E-mail have finally borne
fruit.
I've had a report today of a HOHOHO.EXE received via E-mail that has a lovely
little virus bundled in. The virus is WIN95.CIH, and appears to be
particularly nasty. It attacks harddrives, the Master Boot Record of the PC
AND tries to write to the PC's Flash BIOS; which , if successful, will disable
the PC.
If you receive a message with this attachment, please be aware that it MAY
have a virus attached.
DO NOT RUN THIS .EXE!!
Also, this does not mean that other christmas .EXEs are clean....
Currently, the Innoculan PC client with a current virus signature file SEEMS
to be able to trap and clean it. We are looking at other virus scanners to see
if they are also capable of finding it.
Please warn your staff that this exists and has already affected some users.
If you have any questions, please contact me via E-mail.
See below for a more technical description of the virus.
Robert M. Chute
Senior Technical Architect - Groupware
Technology and Science Secretariat
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Win95.CIH
This is a Windows95 specific parasitic PE files (Portable Executable) infector
about 1Kbyte of length. This virus was found "in-the-wild" in Taiwan in June
1998 - it was posted by the virus author to a local Internet conference as a
some utility. Within a week the virus was found in Austria, Australia, Israel,
United Kingdom, and was also reported from several other countries
(Switzerland, Sweden, USA, Russia, Chile and the list keeps growing).
The virus installs itself into the Windows memory, hooks file access calls and
infects EXE files that are opened. Depending on the system date (see below)
the virus runs its trigger routine. The virus has bugs and in some cases halts
the computer when an infected application is run.
The virus' trigger routine operates with Flash BIOS ports and tries to
overwrite Flash memory with "garbage". This is possible only if motherboard
and chipset allow to write to Flash memory. Usually writing to Flash memory
can be disabled by a DIP switch, however this depends on the motherboard
design. Unfortunately, there are modern motherboards that cannot be protected
by a DIP switch - also, some of them do not pay attention for switch position
and this protection has no effect at all. Some other motherboard designs
provide write protection that can be disabled/overriden by software.
During tests in our lab the virus did not overwrite the Flash BIOS and just
halted the computer. We do however have reports from other sources telling
that the virus really is able to mess it up.
The trigger routine then overwrites data on all installed hard drives. The
virus uses direct disk write calls to achieve this and bypasses standard BIOS
virus protection while overwriting the MBR and boot sectors.
There are three virus versions known, which are very closely related and only
differ in few parts of their code. They have different lengths, texts inside
the virus code and trigger date:
Length Text Trigger date Found In-The-Wild
1003 CCIH 1.2 TTIT on April 26th YES
1010 CCIH 1.3 TTIT on April 26th NO
1019 CCIH 1.4 TATUNG on 26th of any month YES - many reports
Technical details
While infecting a file the virus looks for "caves" in the file body. These
caves are a result of the PE file structure: all file sections are aligned by
a value that is defined in PE file header, and there are not used blocks of
file data between the end of previous section and next one. The virus looks
for these caves and writes its code into them. The virus then increases the
size of sections by the necessary values. As a result the file length is not
increased while infecting.
If there is a cave of enough size, the virus saves its code in one section.
Otherwise it splits its code into several parts and saves them to the end of
several sections. As a result the virus code may be found as set of pieces,
not as a single block in infected files.
The virus also looks for a cave in the PE header. If there is a not used block
not less than 184 bytes of length, the virus writes its startup routine to
there. The virus then patches the entry address in the PE header with a value
that points to the startup routine placed in the header. This is the same
trick that was used in the "Win95.Murkry" virus: address of program entry
points not to some file section, but to file header - out of loadable file
data. Despite this, infected programs are run with no problems - Windows does
not pay attention for such "strange" files, loads the file header into the
memory, then file sections, and then passes control to the virus startup
routine in PE header.
When the virus startup routine takes control, it allocates a block of memory
by using the PageAllocate VMM call, copies itself to there, locates other
blocks of virus code and also copies them to allocated block of memory. The
virus then hooks system IFS API and returns control to the host program.
The most interesting thing in this part of the virus code is that the virus
uses quite complex tricks to jump from Ring3 to Ring0: when the virus jumps to
newly allocated memory its code is then executed as Ring0 routine, and the
virus is able to hook the file system calls (it is not possible in Ring3,
where all users applications are run).
The IFS API virus handler intercepts only one function - file opening. When PE
.EXE files are opened, the virus infects them, provided there are caves of
enough size. After infection, the virus checks the file date and calls trigger
routine (see above).
While running its trigger routine the virus uses direct access to Flash BIOS
ports and VxD direct disk access calls (IOS_SendCommand).
Detection and Disinfection tips can be found in the Win95.CIH FAQ
Document history:
Text originally posted: June-08-1998
Text updated: June-30-1998
Text updated: July-01-1998
CIH FAQ added: July-14-1998
(Detection for this virus was added in Weekly update 980607)
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