發信人: triton (半顆勇敢的心), 信區: Virus 

標  題: 關于CIH病毒的英文說明(轉自清華) 

發信站: 武漢白云黃鶴站 (Thu Sep  3 21:52:43 1998) , 站內信件 

  

發信人: bluesea (藍海), 信區: Virus 

標  題: Win95.CIH 的詳細信息 

發信站: BBS 水木清華站 (Thu Aug 27 00:31:08 1998) 

  

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) 

  

  

  

-- 

上帝創造貓，是為了讓人類體驗撫摸老虎的快樂。 

發信人: bluesea (藍海), 信區: Virus 

標  題: Win95.CIH FAQ 

發信站: BBS 水木清華站 (Thu Aug 27 00:31:56 1998) 

  

Win95.CIH FAQ 

  

  

    What is this Win95.CIH virus, what does it do ? 

    I think my PC may be infected... how do I find out? 

    How can I disinfect my PC from Win95.CIH with build 120 

    Build 120 only: Why do I have to go into command line mode for proper 

    disinfection? 

    After disinfection, I still find traces of CIH in some files (notably the 

    "CIH" string), but a scan shows the files as clean. 

    Is Kaspersky Lab working on making it easier to remove this virus (without 

    having to go through e.g. command line mode) ? 

    Ouch - it's too late! Win95.CIH has left my machine in unbootable state. 

    What can I do? 

    How can I prevent the possible damages Win95.CIH may cause? 

  

  

  

What is this Win95.CIH virus, what does it do ? 

    A detailed description is available in the AVP Virus Encyclopedia 

    I think my PC may be infected... how do I find out? 

  

    NEW: if you use build 122 of AVP 3.0/32 you do no longer need to go 

        through the procedure of using the DOS version! 

        AVP32 build 122 has improved abilities to disinfect Windows viruses, 

        including the CIH virus. 

        First of all, AVP32 will detect and disinfect the CIH virus in system 

        memory. The virus code will stay in Windows memory, but will get patched 

  

        in such a way that the virus would not be able to infect new files or 

        prevent file disinfection. 

        AVP32 then scans itself for the virus infection. If it is infected, 

        AVP32 will disinfect itself, restart and re-scan the Windows memory - 

        this is necessary to be sure that the scanning procedure will be 

        processed under a disinfected system environment. 

        Select all disks and run AVP32 scanning procedure. While scanning AVP32