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FreeBSD-SA-96:11:security compromise from man page utility Print E-mail
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Posted by Team   
FreeBSD The man program is setuid to the "man" user. By executing a particular sequence of commands, an unprivileged local user may gain the access privileges of the "man" user. However, root access could be obtained with further work.

FreeBSD-SA-96:11                                            Security Advisory
Revised: Wed May 22 00:11:46 PDT 1996                           FreeBSD, Inc.

Topic:          security compromise from man page utility

Category:       core
Module:         man
Announced:      1996-05-21
Affects:        FreeBSD 2.0, 2.0.5, 2.1, 2.1-stable, and 2.2-current
Corrected:      2.1-stable and 2.2-current as of 1996-05-21
FreeBSD only:   yes



I.   Background    

     FreeBSD replaced the standard BSD manual page reader with
     code developed by a third party to support compressed manual
     pages.  A bug was found in the manual page reader which can
     allow an unprivileged local user to compromise system security
     in a limited fashion.  This problem is present in all source
     code and binary distributions of FreeBSD version 2.x released
     before 1996-05-21.

II.  Problem Description

     The man program is setuid to the "man" user.  By executing a
     particular sequence of commands, an unprivileged local user
     may gain the access privileges of the "man" user.  However,
     root access could be obtained with further work.

III. Impact

     The "man" user has no particular special privileges, it is
     the owner of the /usr/share/man/cat[0-9] directory hierarchy.
     Unformatted system manual pages are owned by the "bin" user.
     However, further exploits once "man" is obtained could
     possibly allow a local user to obtain unlimited access via
     a trojan horse.

     This vulnerability can only be exploited by users with a valid
     account on the local system.

IV. Workaround

     One may simply disable the setuid bit on the /usr/bin/man file.
     This will disable caching of formatted manual pages, no system
     functionality will be lost.  This workaround will suffice for
     all versions of FreeBSD affected by this problem.
     As root, execute the command:

         # chmod u-s /usr/bin/man

     then verify that the setuid permissions of the files have been
     removed.  The permissions array should read "-r-xr-xr-x" as
     shown here:

         # ls -l /usr/bin/man
         -r-xr-xr-x  1 man  bin  28672 May 19 20:38 /usr/bin/man

     We also suggest applying the following patch to the source
     distribution so that the man program will not be installed
     setuid man should you rebuild from sources:

    *** /usr/src/gnu/usr.bin/man/man/Makefile   Sun Feb 25 13:39:52 1996
    --- /usr/src/gnu/usr.bin/man/man/Makefile   Wed May 22 00:13:05 1996
    *** 1,7 ****
      PROG=     man
      SRCS=     man.c manpath.c glob.c
    - BINMODE=4555
    - BINOWN=   man
      .if exists(${.CURDIR}/../lib/obj)
      LDADD=  -L${.CURDIR}/../lib/obj -lman
    --- 1,5 ----

V. Solution

     The FreeBSD team is in the process of rewriting portions of
     the manual program to avoid this and similar vulnerabilities.
     This security advisory will be updated when a complete solution
     is available.

FreeBSD, Inc.

Web Site:             
Confidential contacts:
PGP Key:              
Security notifications:
Security public discussion:

Notice: Any patches in this document may not apply cleanly due to
        modifications caused by digital signature or mailer software.
        Please reference the URL listed at the top of this document
        for original copies of all patches if necessary.

Version: 2.6.2

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