Virus Name: GOLD-BUG
Aliases: AU, GOLD, GOLD-FEVER, GOLD-MINE
V Status: New, Research
Discovery: January, 1994
Symptoms: CMOS checksum failure; Creates files with no extension; Modem
answers on 7th ring; BSC but it is hidden; Most virus scanners
fail to run or are Deleted; CHKLIST.??? files deleted.
Origin: USA
Eff Length: 1,024 Bytes
Type Code: SBERaRbReX - Spawning Color Video Resident and Extended HMA
Memory Resident Boot-Sector and Master-Sector Infector
Detection Method: None
Removal Instructions: See Below

General Comments:

GOLD-BUG is a memory-resident multipartite polymorphic stealthing
boot-sector spawning anti-antivirus virus that works with DOS 5 and
DOS 6 in the HIMEM.SYS memory. When an .EXE program infected with the
GOLD-BUG virus is run, it determines if it is running on an 80186 or
better, if not it will terminate and not install. If it is on an
80186 or better it will copy itself to the partition table of the hard
disk and remain resident in memory in the HMA (High Memory Area) only
if the HMA is available, ie. DOS=HIGH in the CONFIG.SYS file else no
infection will occur. The old partition table is moved to sector 14
and the remainder of the virus code is copied to sector 13. The virus
then executes the spawned associated file if present. INT 13 and
INT 2F are hooked into at this time but not INT 21. The spawning
feature of this virus is not active now.

When the computer is rebooted, the virus goes memory resident in the
color video memory. Also at this time the GOLD-BUG virus removes
itself from the partition table and restores the old one back. Unlike
other boot-sector infectors, it does not use the top of memory to
store the code. CHKDSK does not show a decrease in available memory.
At this time it only hooks INT 10 and monitors when the HMA becomes
available. Once DOS moves into the HMA, then GOLD-BUG moves into the
HMA at address FFFF:FB00 to FFFF:FFFF. If the HMA never becomes
available, ie. DOS loaded LOW or the F5 key hit in DOS 6 to bypass the
CONFIG.SYS, then the virus clears itself from the system memory when
the computer changes into graphics mode. If it moves to the HMA, it
hooks INT 13, INT 21 and INT 2F and then rewrites itself back to the
partition table. The GOLD-BUG virus also has some code that stays
resident in the interrupt vector table to always make the HMA
available to the virus. The full features of the virus are now
active.

The GOLD-BUG virus will infect the boot sector of 1.2M diskettes.
The virus copies itself to the boot sector of the diskette and moves
a copy of the boot sector to sector 28 and the remainder of the code
is copied to sector 27. These are the last 2 sectors of the 1.2M disk
root directory. If there are file entries on sector 27 or 28 it will
not overwrite them with the virus code. It will infect 1.2M disks in
drive A: or B: If a clean boot disk is booted from drive A: and you
try to access C: you will get an invalid drive specification.

The boot-sector infection is somewhat unique. If the computer is
booted with a disk that contains the GOLD-BUG virus, it will remain in
video memory until the HMA is available and then infect the hard disk.
Also at this time, it will remove itself from the 1.2M disk. The
virus will never infect this disk again. It makes tracking where you
got the virus from difficult in that your original infected disk is
not infected anymore.

If an .EXE file less than 64K and greater then 1.5K is executed,
GOLD-BUG will randomly decide to spawn a copy of it. The .EXE file is
renamed to the same file name with no extension, ie. CHKDSK.EXE
becomes CHKDSK. The original file attributes are then changed to
SYSTEM. An .EXE file with the same name is created. This .EXE file
has the same length, file date and attributes as the original .EXE
file. This spawning process will not make a copy on a diskette
because it might be write protected and be detected; but it will make
a spawn .EXE file on a network drive. When a spawned file is created,
CHKLIST.??? of the current directory is also deleted. The .EXE file
that is created is actually a .COM file; it has no .EXE header.

The GOLD-BUG virus is very specific as to what type of .EXE files it
will spawn copies. It will not spawn any Windows .EXE files or any
other .EXE files the use the new extended .EXE header except those
that use the PKLITE extended .EXE header. This way all Windows
programs will continue to run and the virus will still be undetected.

The GOLD-BUG virus is also Polymorphic. Each .EXE file it creates
only has 2 bytes that remain constant. It can mutate into 128
different decription patterns. It uses a double decription technique
that involves INT 3 that makes it very difficult to decript using a
debugger. The assembly code allowed for 512 different front-end
decripters. Each of these can mutate 128 different ways.

The GOLD-BUG virus incorporates an extensive steathing technique. Any
time the hard disk partition table or boot sector of an infected
diskette is examined, the copy of the partition table or boot sector
is returned. If a spawned .EXE file is opened to be read or executed;
the GOLD-BUG virus will redirect to the original file. Windows 3.1
will detect a resident boot-sector virus if the "Use 32 Bit Access" is
enabled on the "Virtual Memory" option. GOLD-BUG will disconnect
itself from the INT 13 chain when Windows installs and reconnect when
Windows uninstalles to avoid being detected. When Windows starts, the
GOLD-BUG virus will copy the original hard disk partition table back.
When Windows ends, the GOLD-BUG virus will reinfect the partition
table.

The GOLD-BUG virus also has an extensive anti-antivirus routine. It
can install itself with programs like VSAFE.COM and DISKMON.EXE
resident that monitor changes to the computer that are common for
viruses. It writes to the disk using the original BIOS INT 13 and not
the INT 13 chain that these types of programs have hooked into. It
hooks into the bottom of the interrupt chain rather than changing and
hooking interrupts; very similar to the tunneling technique. If the
GOLD-BUG virus is resident in memory, any attempts to run most virus
scanners will be aborted. GOLD-BUG stops any large .EXE file
(greater than 64k) with the last two letters of "AN" to "AZ". It will
stop SCAN.EXE, CLEAN.EXE, NETSCAN.EXE, CPAV.EXE, MSAV.EXE, TNTAV.EXE,
etc., etc. The SCAN program will either be deleted or an execution
error will return. Also, GOLD-BUG will cause a CMOS checksum failure
to happen next time the system boots. GOLD-BUG also erases
"CHKLIST.???" created by CPAV.EXE and MSAV.EXE. Programs that do an
internal checksum on themselves will not detect any changes. The
Thunder Byte Antivirus programs contain a partition table program that
claims it can detect all partition table viruses. GOLD-BUG rides
right through the ThunderByte partition virus checker.

The GOLD-BUG virus detects a modem. If you received an incoming call
on the modem line, GOLD-BUG will output a string that will set the
modem to answer on the seventh ring.

If a program tries to erase the infected .EXE file, the original
program and not the infected .EXE file is erased.

The text strings "AU", "1O7=0SLMTA", and "CHKLIST????" appear in the
decripted code. The virus gets it name from "AU", the chemical
element "GOLD". The text string "CHKLIST????" is actually executable
code.

The GOLD-BUG virus has two companion viruses that it works with. The
DA'BOYS virus is also a boot-sector infector. It is possible to have
a diskette with two boot-sector viruses. GOLD-BUG hides the presence
of the DA'BOYS virus from the Windows 3.1 startup routine. GOLD-BUG
removes the DA'BOYS virus from the INT 13 chain at the start of
Windows and restores it when Windows ends. The GOLD-BUG virus works
with the XYZ virus; it reserves the space FFFF:F900 to FFFF:FAFF in
the HMA for the XYZ virus so it can load as well.

To remove the GOLD-BUG virus, change DOS=HIGH to DOS=LOW in the
CONFIG.SYS, then reboot. Once the system comes up again, reboot from
a clean boot disk. The Virus has now removed itself from the
partition table and memory. With the ATTRIB command check for files
with the SYSTEM bit set that don't have any extension. Delete the
.EXE file associated with the SYSTEM file. Using ATTRIB remove the
SYSTEM attribute. Rename the file with no extension to an .EXE file.
Format each diskette or run SYS to remove the virus from the boot
sector of each 1.2M disk. Any spawned .EXE files copied to diskette
need to be deleted.

Several variations of this virus can exist. The assembly code allowed
for 14 features to be turned on or off: Delete Scanners, Check for
8088, Infect at Random, Deflect Delete, CMOS Bomb, File Reading
Stealth, Same File Date, Double Decription, Execute Spawned, Modem
Code, Anti-Antivirus, Polymorphic, Multipartite and 720K or 1.2M
Diskette Infection. Some of these features can be disabled and more
code added to change the characteristics of this virus.