SpamAssassin Bug Upsets Global Email System

A New Year bug in leading anti-spam software code caused a glitch in the international email system in the early hours of 2010, according to a UK blogger.

The blogger, Mark Cardwell, spotted that SpamAssassin was upping the spam score of any email sent with a date after 2009 due to an error in the ‘FH_DATE_PAST_20XX’ rule the software uses to weed out email that had a header date at an indefinite future date that is often a signature in spam.

Many of the world’s leading ISPs implement SpamAssassin as a first line of defense against spam – and the developers did not spot the error in versions 3.2.0 thru 3.2.5 that meant many emails received undue high spam alert scores.

Fortunately, the ‘FH_DATE_PAST_20XX’ rule is just one of many that combines to stop spam, and on its own was not sufficient to kill messages, but the number of false positives would have hugely increased.

These false positives were reported in Sweden, Germany, and The Netherlands. Daniel Axster, CEO of Swedish open source anti-spam company CronLab, claims the effects of the bug would have been global, affecting every country as the clock ticked past midnight on New Year’s Eve.

“Almost all ISPs use the standard rule set with some modifications,” he said. “The problem probably affected providers for anything from minutes and hours to days in some cases.”

According to Axster, providers should update filters regularly, archive spam for a month or more in case of problems, and offer end users a mechanism to check their filtered emails for false positives.

“Customers should simply not accept having their emails deleted if suspected as spam, but rather have them stored for a while so the ISP can do further analysis on the emails,” he said. “ISPs and filtering providers need to up their game.”

SpamAssassin quickly sent out a fix after being informed of the bug and set up a web site help page.