Anders Kaseorg and Evan Broder reported a flaw in the way sudo handled duplicated environment variables. When sudo set certain environment variables (such as PATH set to securepath value, or special sudo environment variables SUDO), the value overwrote first value from user's environment (if it had been preserved and had not removed previously due to envreset / envkeep / envdelete settings), but left following environment variables with the same name unchanged.

This problem can be used to override securepath setting from /etc/sudoers file for shell scripts executed using sudo, as bash uses last PATH environment variable value. In configurations where securepath is used to enforce sane PATH setting for shell scripts, this can allow users with the privileges to run some script using sudo to run arbitrary command with the privileges of the target user.

Upstream fixes to handle duplicated environment variables: http://www.sudo.ws/repos/sudo/rev/3057fde43cf0 http://www.sudo.ws/repos/sudo/rev/a09c6812eaec

This issue affects sudo packages shipped in Red Hat Enterprise Linux 5, however not the default configuration. In default configuration, no securepath is set. envreset is used by default, and PATH is not preserved during the environment reset (unlike the upstream sudo default).

The sudo packages in Red Hat Enterprise Linux 3 and 4 do not allow setting securepath in the /etc/sudoers, there is no compile-time default for the securepath either. Whether the user PATH setting is preserved depends on envreset / envdelete configuration.

Current Fedora configuration specifies securepath, but also removes PATH from the environment by default.

Incomplete blacklist vulnerability in sudo 1.6.8 and earlier allows local users to gain privileges via the (1) SHELLOPTS and (2) PS4 environment variables before executing a bash script on behalf of another user, which are not cleared even though other variables are.

Multiple race conditions in the (1) Sudo monitor mode and (2) Sysjail policies in Systrace on NetBSD and OpenBSD allow local users to defeat system call interposition, and consequently bypass access control policy and auditing.