Updated Sendmail packages are available to fix a vulnerability that may allow remote attackers to gain root privileges by sending a carefully crafted message. These packages also fix a security bug if sendmail is configured to use smrsh.
Sendmail is a widely used Mail Transport Agent (MTA) which is included in all Red Hat Linux distributions. During a code audit of Sendmail by ISS, a critical vulnerability was uncovered that affects unpatched versions of Sendmail prior to version 8.12.8. A remote attacker can send a carefully crafted email message which, when processed by sendmail, causes arbitrary code to be executed as root. We are advised that a proof-of-concept exploit is known to exist, but is not believed to be in the wild. Since this is a message-based vulnerability, MTAs other than Sendmail may pass on the carefully crafted message. This means that unpatched versions of Sendmail inside a network could still be at risk even if they do not accept external connections directly. In addition, the restricted shell (SMRSH) in Sendmail allows attackers to bypass the intended restrictions of smrsh by inserting additional commands after "||" sequences or "/" characters, which are not properly filtered or verified. A sucessful attack would allow an attacker who has a local account on a system which has explicitly enabled smrsh to execute arbitrary binaries as themselves by utilizing their .forward file. All users are advised to update to these erratum packages. For Red Hat Linux 8.0 we have included Sendmail version 8.12.8 which is not vulnerable to these issues. For all other distributions we have included a backported patch which corrects these vulnerabilities. Red Hat would like to thank Eric Allman for his assistance with this vulnerability.