Rare Linux virus on the loose
By James Middleton  [03-01-2002]

It has emerged in the last week that another of those
rare Linux viruses may be on the loose. And this one
has strong similarities to October's Remote Shell
Trojan (RST) that was largely dismissed by the Linux
community.

In a posting to a security mailing list at the end of
December, SecurityFocus brought 'RST.b' to the
internet community's attention.

The researchers warned that the culprit carrying the
virus is likely to be "some exploit being passed
around, possibly a Secure Shell one". Linux users are
advised not to run exploits from unknown sources.
Once it has gained a foothold into the system, it
installs a back door and attempts to escalate its
permissions to root privileges.

The basic differences to the October version are that
the new virus tries to communicate with a machine on a
different IP address to the original RST, and the
backdoor operates on the Exterior Gateway Protocol
instead of the User Datagram Protocol.

Like the original RST, the virus infects binary files
in the Linux Executable and Linking Format (ELF). 
RST.b infects the start address in ELF headers with an
address that points to its own code. So when an
infected program is run, a parent string forks off to
run the original code so as to avoid suspicion, while
a child string "takes care of the evil stuff",
according to researchers at Lockeddown.net.

"Not only do we have a virus spreading, but it is
opening up the infected boxes to attackers," they
added.

A SecurityFocus researcher who attempted to contact
the host of the web server that had infected the
machines said: "The response I got indicated that 'his
account was terminated a few weeks ago'. I received no
response to a later request for clarification."

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