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Date: Wed, 27 Feb 2013 11:23:29 -0500
From: "Todd C. Miller" <Todd.Miller@...rtesan.com>
To: oss security list <oss-security@...ts.openwall.com>
Subject: CVE request: sudo authentication bypass when clock is reset

Sudo 1.8.6p7 and 1.7.10p7 are now available which include a fix
for the following bug:

Sudo authentication bypass when clock is reset

Summary:
    When a user successfully authenticates with sudo, a time stamp
    file is updated to allow that user to continue running sudo
    without requiring a password for a preset time period (five
    minutes by default).  The user's time stamp file can be reset
    using "sudo -k" or removed altogether via "sudo -K".

    A user who has sudo access and is able to control the local
    clock (common in desktop environments) can run a command via
    sudo without authenticating as long as they have previously
    authenticated themselves at least once by running "sudo -k" and
    then setting the clock to the epoch (1970-01-01 01:00:00).

    The vulnerability does not permit a user to run commands other
    than those allowed by the sudoers policy.

Sudo versions affected:
    Sudo 1.6.0 through 1.7.10p7 and sudo 1.8.0 through 1.8.6p7.

Details:
    By default, sudo displays a lecture when the user's time stamp
    file is not present.  In sudo 1.6, the -k option was changed
    to reset the time stamp file to the epoch rather than remove
    it to prevent the lecture from being displayed the next time
    sudo was run.  No special case was added for handling a time
    stamp file set to the epoch since the clock should never
    legitimately be set to that value.

    However, there are two common ways for the clock to be reset
    to the epoch.  The first way is when the clock is reset due to
    a fully drained battery on some systems.  The other way is by
    a user logged in to a desktop environment that allows changes
    to the date and time.

    As long as the user has successfully run sudo before, they are
    able to run "sudo -k" to reset the time stamp file.  This action
    does not require a password and is not logged.  If the user is
    also able to reset the date and time to the epoch (1970-01-01
    01:00:00), they will be able to run sudo without having to
    authenticate.

Impact:
    The flaw may allow someone with physical access to a machine
    that is not password-protected to run sudo commands without
    knowing the logged in user's password.  On systems where sudo
    is the principal way of running commands as root, such as on
    Ubuntu and Mac OS X, there is a greater chance that the logged
    in user has run sudo before and thus that an attack would
    succeed.

Fix:
    The bug is fixed in sudo 1.8.6p7 and 1.7.10p7.  These versions
    will ignore a time stamp file that is set to the epoch.

Workaround:
    Using "sudo -K" instead of "sudo -k" will completely remove the
    time stamp file instead of just resetting it.

Credit:
    I'd like to thank Marco Schoepl for finding and reporting this
    long-standing bug.

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