WU-FTPD contains a format string vulnerability that manifests when WU-FTPD is configured to use RFC 931 authentication and is run in debug mode. A crafted identd response could be used to execute arbitrary code on a vulnerable server.
A format string vulnerability exists in the Washington University FTP daemon, WU-FTPD. WU-FTPD is a widely deployed FTP daemon that runs on UNIX and Linux systems and is included in a number of distributions. WU-FTPD can be compiled to use RFC 931 authentication using the '--enable-rfc931' configuration option, in which the server requests user information from the ident daemon running on an FTP client host. Note that RFC 1413 (Identification Protocol) obsoletes RFC 931 (Authentication Server). WU-FTPD can also be run in debugging mode using the '-d' option. Under these conditions, WU-FTPD logs connection information using syslog(3) calls without providing format string specifiers or adequately validating client identd responses. As a result, a crafted identd response containing user-supplied format string specifiers is interpreted by syslog(3), possibly overwriting arbitrary locations in memory. By carefully designing such a request an attacker may execute arbitrary code with the privileges of WU-FTPD.
This vulnerability is potentially exploitable by any user who is able to log in to a vulnerable server, including users with anonymous access. The intruder must also be able to control the response of the auth or ident daemon. If successful, an attacker may be able to execute arbitrary code with the privileges of WU-FTPD, typically root.
A remote attacker may be able to execute arbitrary code with the privileges of WU-FTPD, typically root.
Disable RFC 931 AuthenticationDo not run WU-FTPD configured with '--enable-RFC931'.Disable Debug ModeDo not run WU-FTPD with the '-d' option.Block or Restrict AccessBlock or restrict access to the port used by WU-FTPD, typically 21/tcp. It may be possible to use TCP Wrapper or a similar technology to provide improved access control and logging. Additionally, an application-level firewall may be able to filter requests made to WU-FTPD. Note that potential exploit strings would be transmitted from 113/tcp on clients to the WU-FTPD server that requested RFC 931 authentication.Disable Vulnerable ServiceDisable WU-FTPD until a patch can be applied.
WU-FTPD Development Group
The CERT Coordination thanks INTEXXIA for bringing this matter to our attention.
This document was written by Art Manion.
|Date First Published:||2001-11-29|
|Date Last Updated:||2001-12-17 19:48 UTC|