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Summary:
A bug was introduced in Sudo's group matching code in version
1.6.9 when support for matching based on the supplemental group
vector was added. This bug may allow certain users listed in
the sudoers file to run a command as a different user than their
access rule specifies.
Patch for OpenBSD 4.3:
ftp://ftp.openbsd.org/pub/OpenBSD/patches/4.3/common/011_sudo.patch
Patch for OpenBSD 4.4:
ftp://ftp.openbsd.org/pub/OpenBSD/patches/4.4/common/011_sudo.patch
These patches are also available in the OPENBSD_4_3 and OPENBSD_4_4
stable CVS branches. OpenBSD-current is not affected.
Details:
Given a sudoers rule like the following:
bob ALL=(%users) ALL
user bob should only be able to run commands as a user that
is a member of the Unix group users.
However, due to the bug, if bob is himself a member of users,
he will actually be able to run a command as any user.
Impact:
The bug only impacts sudoers configurations where a Unix group
is used in the RunAs list, which is (%users) in the example above.
For example, the following sudoers rule is not affected
by the bug:
bob ALL = ALL
Credit:
This problem was brought to my attention by Harald Koenig.
Background:
Code was added to sudo version 1.7.0 to cache the user's
supplemental group vector and use it in group matches. When
this changed was back-ported to sudo version 1.6.9, the check
to only use the supplemental groups when matching against the
invoking user got dropped.
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