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__________________________________________________________
The U.S. Department of Energy
Computer Incident Advisory Capability
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__________________________________________________________
INFORMATION BULLETIN
FreeBSD setlocale() Vulnerability
February 7, 1997 00:00 GMT Number H-26
______________________________________________________________________________
PROBLEM: A vulnerability for all binaries due to setlocale() being
called from crt0.o.
PLATFORM: FreeBSD 2.1.6 and earlier systems
DAMAGE: If exploited, this vulnerability could be used to gain root
access to the system.
SOLUTION: Apply the patches described below.
______________________________________________________________________________
VULNERABILITY Because of the severity of this security hole, a full update
ASSESSMENT: release for FreeBSD 2.1.6 will be released very shortly, that
release being provisionally assigned the version number of
2.1.7.
______________________________________________________________________________
[ Start FreeBSD Advisory ]
=============================================================================
FreeBSD-SA-97:01 Security Advisory
Revised: Wed Feb 05 09:58:56 PDT 1997 FreeBSD, Inc.
Topic: setlocale() bug in all released versions of FreeBSD
Category: core
Module: libc
Announced: 1997-02-05
Affects: FreeBSD 2.1.6 and earlier systems suffer from this
vulnerability for all binaries due to setlocale() being
called from crt0.o.
Corrected: 1997-02-05 -stable, 1996-11-27 -current and RELENG_2_2 sources
Source: FreeBSD specific bug
FreeBSD only: unknown
Patches: ftp://freebsd.org/pub/CERT/patches/SA-97:01/
=============================================================================
I. Background
The setlocale() call contains a number of potential exploits through
string overflows during environment variable expansion. Because
the 2.1.6 and earlier versions of FreeBSD called setlocale() in
the C runtime code, the problem is especially acute there in that it
essentially effects all binaries on the system.
In FreeBSD 2.2 BETA and later releases, the setlocale() call was
removed from crt0.c and the exploit closed through additional checks.
There has also been some confusion over the implications of loading
locale data by privileged programs. The facility for a user to supply
their own (possibly corrupt or abused) locale data to non-privileged
processes was removed in all releases on 1997-02-04. This was
originally a debugging facility that got little use and the user can now
only direct system binaries to load system administrator sanctioned
locale files.
This problem is present in all source code and binary distributions of
FreeBSD released on or before 1996-11-27.
II. Problem Description
The setlocale() library function looks for the environment variable
"PATH_LOCALE" in the current process's environment, and if it exists,
later copies the contents of this variable to a stack buffer without
doing proper bounds checking. If the environment variable was specially
initialized with the proper amount and type of data prior to running a
setuid program, it is possible to cause the program to overflow its stack
and execute arbitrary code which could allow the user to become root.
III. Impact
Any binary linked on a system with setlocale() built into crt0.c (see
list of affected releases in section I above) or which calls setlocale()
directly has the buffer overrun vulnerability.
If this binary has the setuid or setgid bits set, or is called by
another setuid/setgid binary (even if that other setuid/setgid binary
does not have this vulnerability), unauthorized access may be allowed.
IV. Solution(s)
Recompiling libc with the following patches and then recompiling all
staticly linked binaries (all in /sbin and /bin as well as chflags,
gunzip, gzcat, gzip, ld, tar and zcat in /usr/bin) eliminates this
vulnerability in FreeBSD 2.1.6 and earlier releases:
However, a full solution may require a re-link of all setuid/setgid
local binaries or all local binaries likely to be called from another
setuid/setgid program that were originally linked statically under
one of the affected OSs. Dynamically linked executables will benefit
directly from this patch once libc is rebuilt and reinstalled and
do not need to be relinked.
Because of the severity of this security hole, a full update release for
FreeBSD 2.1.6 will also be released very shortly, that release being
provisionally assigned the version number of 2.1.7.
Index: lib/libc/locale/collate.c
===================================================================
RCS file: /home/ncvs/src/lib/libc/locale/collate.c,v
retrieving revision 1.4.4.2
diff -c -r1.4.4.2 collate.c
*** collate.c 1996/06/05 02:47:55 1.4.4.2
--- collate.c 1997/02/05 10:21:59
***************
*** 64,70 ****
__collate_load_error = 1;
if (!encoding)
return -1;
! if (!path_locale && !(path_locale = getenv("PATH_LOCALE")))
path_locale = _PATH_LOCALE;
strcpy(buf, path_locale);
strcat(buf, "/");
--- 64,70 ----
__collate_load_error = 1;
if (!encoding)
return -1;
! if (!path_locale)
path_locale = _PATH_LOCALE;
strcpy(buf, path_locale);
strcat(buf, "/");
Index: lib/libc/locale/rune.c
===================================================================
RCS file: /home/ncvs/src/lib/libc/locale/rune.c,v
retrieving revision 1.2.6.3
diff -c -r1.2.6.3 rune.c
*** rune.c 1996/06/05 02:47:59 1.2.6.3
--- rune.c 1997/02/05 10:22:00
***************
*** 71,77 ****
return(0);
}
! if (!PathLocale && !(PathLocale = getenv("PATH_LOCALE")))
PathLocale = _PATH_LOCALE;
(void) strcpy(name, PathLocale);
--- 71,77 ----
return(0);
}
! if (!PathLocale)
PathLocale = _PATH_LOCALE;
(void) strcpy(name, PathLocale);
Index: lib/libc/locale/setlocale.c
===================================================================
RCS file: /home/ncvs/src/lib/libc/locale/setlocale.c,v
retrieving revision 1.3.4.2.2.1
diff -c -r1.3.4.2.2.1 setlocale.c
*** setlocale.c 1996/06/05 02:48:03 1.3.4.2.2.1
--- setlocale.c 1997/02/05 10:22:00
***************
*** 58,64 ****
int found, i, len;
char *env, *r;
! if (!PathLocale && !(PathLocale = getenv("PATH_LOCALE")))
PathLocale = _PATH_LOCALE;
if (category < 0 || category >= _LC_LAST)
--- 58,64 ----
int found, i, len;
char *env, *r;
! if (!PathLocale)
PathLocale = _PATH_LOCALE;
if (category < 0 || category >= _LC_LAST)
Index: lib/libc/locale/startup_setlocale.c
===================================================================
RCS file: /home/ncvs/src/lib/libc/locale/Attic/startup_setlocale.c,v
retrieving revision 1.2.4.2
diff -c -r1.2.4.2 startup_setlocale.c
*** startup_setlocale.c 1995/08/28 05:06:50 1.2.4.2
--- startup_setlocale.c 1997/02/05 10:22:00
***************
*** 23,29 ****
int found, i, len;
char *env, *r;
! if (!PathLocale && !(PathLocale = getenv("PATH_LOCALE")))
PathLocale = _PATH_LOCALE;
if (category < 0 || category >= _LC_LAST)
--- 23,29 ----
int found, i, len;
char *env, *r;
! if (!PathLocale)
PathLocale = _PATH_LOCALE;
if (category < 0 || category >= _LC_LAST)
=============================================================================
[ End FreeBSD Advisory ]
_______________________________________________________________________________
CIAC wishes to acknowledge the contributions of FreeBSD for the
information contained in this bulletin.
_______________________________________________________________________________
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