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16 February 2009, 14:41

Telnetd exploit on FreeBSD 7

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A posting on the Full Disclosure mailing list has revealed what the FreeBSD Security team call a semi-remote root exploit for the telnetd service in FreeBSD 7, and later. By default, this service is disabled.

To exploit the vulnerability, a maliciously crafted library must be placed on the victim system beforehand, and then an attacker must connect via telnetd, passing the location of that library in the LD_PRELOAD environment variable. The malicious library is then loaded before the /bin/login process and executed as root.

Colin Percival, Security Officer for FreeBSD, recommends that FreeBSD 7.0-RELEASE, 7.1-RELEASE, 7-STABLE, and 8-CURRENT users ensure that telnetd is disabled. Dragonfly BSD is also reportedly vulnerable to the issue, but for a different reason, and patches for it, will not work on FreeBSD.

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