Malicious hackers could exploit a security flaw to gain control of software responsible for transporting three-quarters of internet email.
Details of the buffer overflow vulnerability in Sendmail's Mail Transfer Agent (MTA) were released yesterday by Sendmail and security firm Internet Security Systems (ISS), which discovered the flaw.
Sendmail is the internet's most popular email handling agent. Between 50 and 75 per cent of all internet email uses Sendmail MTA.
A similar exploit in Microsoft's software was responsible for the Slammer virus spreading so rapidly and slowing down internet traffic in January.
Attackers could remotely exploit this vulnerability to gain 'root' or 'superuser' control of vulnerable Sendmail servers, according to ISS.
The vulnerability is especially dangerous because exploits can be delivered by email. Hackers would not need specific knowledge of target servers to be able to launch successful attacks, ISS warned.
If an exploit is developed to take advantage of this vulnerability, the security firm said that email and messaging systems could be affected.
This could lead to extreme latency, complete unresponsiveness, and compromised data integrity in both incoming and outgoing communications.
Sendmail versions 5.79 to 8.12.7 are vulnerable, and the company is urging all users to either upgrade to version 8.12.8 or apply a patch for 8.12.x or older versions.
The latest version and patch can be downloaded from the Sendmail website here.
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