[8lgm]-Advisory-22.UNIX.syslog.2-Aug-1995

[8lgm () 8lgm org ([8LGM] Security Team)]

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                [8lgm]-Advisory-22.UNIX.syslog.2-Aug-1995

VULNERABLE PROGRAMS:

        All programs calling syslog(3) with user supplied data, without
        checking argument lengths.

KNOWN VULNERABLE PLATFORMS:

        SunOS 4.1.*

KNOWN SECURE PLATFORMS:

        None at present.

DESCRIPTION:

        syslog(3) uses an internal buffer to build messages.  However
        it performs no bound checking, and relies on the caller to
        check arguments passed to it.

IMPACT:

        Local and remote users can obtain root access.

REPEAT BY:

        We have written an example exploit to overwrite syslog(3)'s
        internal buffer using SunOS sendmail(8).  However due to the
        severity of this problem, this code will not be made available
        to anyone at this time.  Please note that the exploit was fairly
        straightforward to put together, therefore expect exploits to be
        widely available soon after the release of this advisory.

        Here is a edited sample of using a modified telnet client to
        obtain a root shell through SunOS sendmail(8) on a sparc
        based machine.

        legless[8lgm]% syslog_telnet localhost smtp
        Trying 127.0.0.1 ...
        Connected to localhost.
        Escape character is '^]'.
        220 legless.8lgm.org Sendmail 4.1/SMI-4.1 ready at Sun,\
         27 Aug 95 15:56:27 BST
        mail from: root
        250 root... Sender ok
        rcpt to: root
        250 root... Recipient ok
        data
        354 Enter mail, end with "." on a line by itself
        ^]
        syslog_telnet>

        ### At this point, we provide some information to the modified
        ### telnet client about the remote host.  Then sparc instructions
        ### are sent over the link within the body of the message to
        ### execute a shell.
        ###
        ### As soon as data is finished (with .), sendmail will eventually
        ### report, through syslog(3), data about this message.  syslog's
        ### internal buffer will be overwritten, and our supplied
        ### instructions are executed.

        Hit <cr>, then .<cr>

        .
        /usr/bin/id;
        uid=0(root) gid=0(wheel) groups=0(wheel)
        /bin/sh: ^M: not found
        uptime;
          3:57pm  up  1:25,  5 users,  load average: 0.11, 0.05, 0.00
        /bin/sh: ^M: not found
        exit;
        Connection closed by foreign host.

        ### Here we can see that sendmail has execed a shell as root,
        ### and that we can type commands.  (lines ending in ; are
        ### user input through the telnet client).
        ###
        ### This exploit could be further expanded upon to encapsulate
        ### instructions within the body of a message, which can then
        ### be mailed out to a site (ie without the necessity to connect
        ### directly to the smtp port).  This may be used to bypass
        ### firewalls.

WORKAROUNDS:

        We have two methods to ensure that syslog(3) can not be used in
        the above manner.

        Fix syslog(3), to perform bound checking.  Shared libraries
        can be then fixed to use the new function.  Statically linked
        programs will require rebuilding.

        Alternatively, ensure all calls to syslog(3), by all programs,
        check all arguments passed to syslog(3).

        Ideally both of the above should be implemented.

FIX:

        Contact vendors for fixes.

STATUS UPDATE:

        The file:

        [8lgm]-Advisory-22.UNIX.syslog.2-Aug-1995.README

        will be created on www.8lgm.org.  This will contain updates on
        any further versions which are found to be vulnerable, and any
        other information received pertaining to this advisory.

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