Stoned.Standard

SUMMARY

Stoned.Standard is the basis for many viruses. Stoned.Standard infects the DOS boot sector on floppy disks and the master boot record (MBR) of the first hard drive (80h). It is not a stealth virus, does not infect files, and cannot infect over networks.

Threat Assessment

Wild

• Wild Level: Low
• Number of Infections: 0 - 49
• Number of Sites: 0 - 2
• Geographical Distribution: Low
• Threat Containment: Easy
• Removal: Easy

Damage

• Damage Level: Low

Distribution

• Distribution Level: Low

TECHNICAL DETAILS

The virus code is one sector in length and it reserves 4K of memory. Thus, on a 640K machine, CHKDSK would report 651,264 bytes of free memory.

On the hard drive, the original MBR is stored on physical sector 7 of the infected drive. The virus stores the original DOS boot sector in the physical sector at side 1, cylinder 0, sector 3 on infected floppy disks (logical sector 11). On 360K floppy disks, this is the last sector of the root directory. It overwrites the last 16 directory entries if the directory is completely full. On larger-capacity floppy disks, it is stored earlier in the root directory.

Upon booting from an infected disk, Stoned.Standard checks the MBR to see if it is infected. If it is not, the virus infects it. This is the only time the hard drive can be infected. If you remove the virus from the MBR while it is active in memory, the MBR is not re-infected. Also, on booting, there is a 1 in 8 chance the virus will beep and display its message.

The infected boot sector or MBR contains the plainly visible message:

Your PC is now stoned! LEGALIZE MARIJUANA!

The message starts at offset 18Ah in the sector. By looking at the floppy boot or MBR sector with a disk editor, you can verify an infection. There is also a fairly common minor variant, which is detected by most anti-virus packages as being the same virus, in which the “LEGALIZE MARIJUANA� portion of the message has been corrupted.

Stoned.Standard was programmed by a University of Wellington student in New Zealand in 1987. By design, the virus infects MBRs and the boot sector of 360K disks. Under such conditions, the virus is relatively benign. However, the virus can damage data on any floppy disk it infects and the probability of damage increases as the capacity of the floppy disk increases. For example, on a 1.44 MB floppy disk, the virus overwrites entries 17-32 in the root.

Recommendations

Symantec Security Response encourages all users and administrators to adhere to the following basic security "best practices":

• Turn off and remove unneeded services. By default, many operating systems install auxiliary services that are not critical, such as an FTP server, telnet, and a Web server. These services are avenues of attack. If they are removed, blended threats have less avenues of attack and you have fewer services to maintain through patch updates.
• If a blended threat exploits one or more network services, disable, or block access to, those services until a patch is applied.
• Always keep your patch levels up-to-date, especially on computers that host public services and are accessible through the firewall, such as HTTP, FTP, mail, and DNS services (for example, all Windows-based computers should have the current Service Pack installed.). Additionally, please apply any security updates that are mentioned in this writeup, in trusted Security Bulletins, or on vendor Web sites.
• Enforce a password policy. Complex passwords make it difficult to crack password files on compromised computers. This helps to prevent or limit damage when a computer is compromised.
• Configure your email server to block or remove email that contains file attachments that are commonly used to spread viruses, such as .vbs, .bat, .exe, .pif and .scr files.
• Isolate infected computers quickly to prevent further compromising your organization. Perform a forensic analysis and restore the computers using trusted media.
• Train employees not to open attachments unless they are expecting them. Also, do not execute software that is downloaded from the Internet unless it has been scanned for viruses. Simply visiting a compromised Web site can cause infection if certain browser vulnerabilities are not patched.