Makers of Sendmail, the popular e-mail transmission software, were taken by surprise over the weekend by a public announcement of another flaw in the program.
Systems affected by the vulnerability include all versions of Sendmail Pro, as well as systems running open-source Sendmail versions prior to 8.12.9, including UNIX and Linux systems. A complete list of affected systems is available from CERT.
CERT said an attacker could gain control of a vulnerable Sendmail server or create a denial of service condition by exploiting the vulnerability, which was discovered by Michal Zalewski. The flaw is considered particularly dangerous since it can be exploited simply by sending a properly formatted e-mail to a vulnerable system, and CERT said the vulnerability has been successfully exploited in laboratory conditions. An e-mail message capable of exploiting the vulnerability would probably pass through a firewall undetected.
The vulnerability is different from the Sendmail flaw identified earlier this month. In that case, the flaw had been discovered several months earlier by US e-security firm Internet Security Systems, who quietly passed on the information to the US Department of Homeland Security. The two bodies then cooperated to develop patches prior to the announcement of the flaw in early March.
The new flaw, however, was evidently publicised soon after its discovery, forcing Sendmail to scramble over the weekend to acknowledge and repair the fault. In its bug notice, Sendmail apologised for releasing the information on the vulnerability on a Saturday. "We apologise for releasing this information today (2003-03-29) but we were forced to do so by an e-mail on a public mailing list which contains information about the security flaw," the company said.
Many software vendors include a version of Sendmail as part of their software packages. With the earlier vulnerability, vendors like HP, IBM and Apple were able to make their own assessment and ready patches before the Internet community was told of the fault.
The premature publicity surrounding the new flaw, however, means that a number of major vendors have no patches available yet. Sendmail has posted patches for earlier versions of Sendmail but is urging users to upgrade to version 8.12.9 wherever possible.
CERT is updating its advisory on the vulnerability as new information becomes available. © ENN