CVE-2012-3440: Race Condition

The sudo packages in Red Hat Enterprise Linux 5 contained a %postun script (executed during the package removal or upgrade) that created a temporary file insecurely. The script did the following:

Remove the "sudoers:" line from nsswitch.conf if it's not modified if grep -q "^sudoers: files ldap$" ""/etc/nsswitch.conf""; then rm -f ""/var/tmp/nsswitch.conf.bak"" && \ touch ""/var/tmp/nsswitch.conf.bak"" && \ grep -v "^sudoers: files ldap$" ""/etc/nsswitch.conf"" > ""/var/tmp/nsswitch.conf.bak"" && \ mv -f ""/var/tmp/nsswitch.conf.bak"" ""/etc/nsswitch.conf"" fi

There was a race condition between the removal of the temporary file and its re-creation using touch. A local attacker could possibly use this to create nsswitch.conf.bak file or symlink after rm -f "/var/tmp/nsswitch.conf.bak" was run and cause the script to overwrite arbitrary file with the contents of the /etc/nsswitch.conf file, or make the script create /etc/nsswitch.conf file with attacker controlled content and permissions. The attack would have to be executed during the sudo package upgrade or removal.

This problem was introduced in the sudo erratum RHSA-2012:0309 which was released in Red Hat Enterprise Linux 5.8:

https://rhn.redhat.com/errata/RHSA-2012-0309.html

The sudo packages in other Red Hat Enterprise Linux versions did not include this %postun script and were not affected this issue.