Perl scripts run via Sudo can be subverted

A flaw in exists in sudo’s environment sanitizing prior to sudo version 1.6.8p12 that could allow a malicious user with permission to run a perl script to execute arbitrary perl code.

All versions prior to 1.6.8p12.

This vulnerability has been assigned CVE-2004-1051 in the Common Vulnerabilities and Exposures database.

The PERL5LIB and PERLLIB environment variables can be used to provide a list of directories in which to look for perl library files before the system directories are searched. It is similar in concept to the LD_LIBRARY_PATH environment variables, only for perl. These variables are ignored if “tainting” is enabled (via the -T switch). The PERL5OPT environment variable specifies additional command line options to be passed to the script which may modify its behavior.

Malicious users with sudo access to run a perl script can use these variables to include and execute their own library file with the same name as a system library file that is included (via the “use” or “require” directives) by the perl script run via sudo.

Exploitation of the bug requires that perl be installed on the machine and that users be granted sudo access to run perl scripts that do not have tainting turned on.

The bug is fixed in sudo 1.6.8p12.

The administrator can add a line at the top of the sudoers file:

Defaults	env_delete+="PERLLIB PERL5LIB PERL5OPT"

which will cause sudo to strip the PERLLIB, PERL5LIB and PERL5OPT environment variables without requiring a recompile. Alternately, the administrator can add a line to the top of sudoers file:

Defaults	env_reset

which will reset the environment to only contain the variables HOME, LOGNAME, PATH, SHELL, TERM, and USER, also preventing this attack.

This problem was brought to my attention by Charles Morris.