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A new worm that, ironically, makes sport of Win-32 systems defended by BlackIce and RealSecure firewall products from Internet Security Systems (ISS) began circulating Saturday.

The worm, dubbed 'witty,' is memory-resident only and propagates via UDP port 4000, and possibly others. While occupied with reproducing itself, it overwrites data on the local hard disk(s), and can render a machine un-bootable if it corrupts the master boot record or partition table, or file allocation tables.

The worm is exceptionally vicious by current standards and implies the presence of a highly motivated spoil-sport, such as a disgtruntled former employee, an envious competitor, or a monumentally dissatisfied customer. Or it could just be a cool bit of retro coding.

By day's end, little witty had infected an estimated 50,000 systems, but because the worm is so destructive, it is unlikely to propagate at such a rate for very long. It also exploits a vulnerability in a limited number of BlackIce and RealSecure editions, further limiting its reach. No doubt all this will be fixed in its next edition.

"Witty" is so named because of its creator's incredibly humourous message in packets sent,

(^.^......insert.witty.message.here .......(^.^)

The worm generates a random IP address and sends itself via UDP to a random destination port. After 20,000 attempts, it writes 65K of data to the local disk(s). It then rinses and repeats, ad nauseum. Because the cycle is so brief, a great deal of damage can be done before an infected machine exhibits signs of corruption. Re-booting will eliminate the worm, but the system may already be damaged enough to fail.

Witty exploits a buffer overflow vulnerability in an ISS ICQ parser called 'PAM' (Protocol Analysis Module). This should not be confused with the better-known Pluggable Authentication Module PAM, which is not in danger.

It is possible to recover data from an un-bootable disk, but many home users are unlikely to know how to do this, and will be forced to re-install their systems, sacrificing their data. Perhaps a class action lawsuit will be in order.

Power users and pros will likely be able to recover at least a decent part of a witty-damaged disk. Of course, any data overwritten will be permanently un-recoverable, and the worm can do considerable harm because it attacks the disk repeatedly until it's caught. Because the worm is memory-resident and never writes itself to disk, the fine products of many renowned AV vendors may fail to detect it.

Recovering data from an un-bootable disk is time-consuming and never foolproof, but power users can employ a DOS utility like DiskEdit, which allows for browsing, copying and pasting; or better, the Linux utility DD_Rescue, which will copy a disk volume to another disk without balking at I/O errors.

Affected systems

According to ISS, the following systems are currently known to be vulnerable:
BlackICE Agent for Server 3.6 ebz, ecd, ece, ecf
BlackICE PC Protection 3.6 cbz, ccd, ccf
BlackICE Server Protection 3.6 cbz, ccd, ccf
RealSecure Network 7.0, XPU 22.4 and 22.10
RealSecure Server Sensor 7.0 XPU 22.4 and 22.10
RealSecure Desktop 7.0 ebf, ebj, ebk, ebl
RealSecure Desktop 3.6 ebz, ecd, ece, ecf
RealSecure Guard 3.6 ebz, ecd, ece, ecf
RealSecure Sentry 3.6 ebz, ecd, ece, ecf

Patches are available from the ISS downloads page. ®

Thomas C Greene is the author of Computer Security for the Home and Small Office, a complete guide to online anonymity, system hardening, encryption, and data hygiene for Windows and Linux, available at discount in the USA, and soon in the UK.

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