The most widely used software for sending Internet e-mail has a flaw that may allow a hacker to seize control of large computers that pass messages between networks, a computer-security company said.
The flaw in Sendmail Inc's software puts Internet messages at risk because a hacker could exploit it to read or delete mail or shut down computer networks. Sendmail, the oldest e-mail software, is used to store and forward messages in systems sold by companies including Sun Microsystems Inc, Hewlett-Packard Co, and International Business Machines Corp.
"It's one of the biggest bugs we've ever found," said Dan Ingevaldson, a researcher with Internet Security Systems Inc, which discovered the vulnerability. "Basically, anything that an administrator could do to the machine, a hacker could do."
Sendmail, based on a program developed in 1981 for transmitting correspondence at the University of California at Berkeley, is installed on more than a million server computers, Sendmail Chairman Greg Olson said. The flaw in the software may allow a hacker to gain access to parts of a machine's memory that are supposed to be off limits. It was found in versions of the software dating back to the late 1980s.
"It's been out there for 15 years. It's really obscure," Olson said.
There is no evidence that any viruses have used the flaw to access e-mail systems, Internet Security said. Internet Security has made software available on its Web site that can prevent hackers from exploiting the vulnerability. Internet Security's Web address is http://www.iss.net.
Computer hackers typically write viruses that affect the most prevalently used software, so the flaw in Sendmail, which carries as much as 75 percent of Internet mail, made it a likely candidate for an attack.
The flaw is exploited by attaching a special string of code to the address or subject lines of e-mail that spills into an overflow area, where a hacker can then install code to gain remote access of a computer, Ingevaldson said.
The "Slammer" virus exploited a similar mechanism in Microsoft Corp's server software. That virus was the fastest to spread ever.
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