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Home » Security Advisories» FreeBSD » Security compromise from man page utility

Security compromise from man page utility

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.

  • Vendor: FreeBSD
  • Vendor ID: SA-96:11
  • Date: May 22, 1996


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=====================================================================
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

Patches: ftp://freebsd.org/pub/CERT/patches/SA-96:11/

=====================================================================

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: http://www.freebsd.org/
Confidential contacts: [email protected]
PGP Key: ftp://freebsd.org/pub/CERT/public_key.asc
Security notifications: [email protected]
Security public discussion: [email protected]

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.
=====================================================================

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