[Global InterSec 2001121001] glibc globbing issues.

Type securityvulns
Reporter Securityvulns
Modified 2001-12-18T00:00:00


Global InterSec LLC http://www.globalintersec.com

GIS Advisory ID: 2001121001 Changed: 12/12/2001 Author: tom.parker@globalintersec.com Reference: http://www.globalintersec.com/adv/glibc-glob-2001121001.txt


The release of this advisory has been earlier than first planned due to RedHats release of information regarding this vulnerability. Redhat are not to blame this time around. However better vendor/researcher coordination is called for.


glibc contains a globbing error which may be remotely exploitable when glob functions are used in software such as ftp daemons.


A remote attacker may execute arbitrary commands via heap corruption.


The glibc glob() function allows programs to search for path names matching specific patterns according the rules used by the shell. Glibc also implements the globfree() function which free()'s memory used earlier by other glob() matches. The glob function itself may encounter errors when handling strings ending with the "{"(0x7b)character. This is due to next_brace_sub() which could cause glob to read memory pages it shouldn't be, eventually causing the program to exit (Normally with SEGV)..

Note: The vulnerability described in CA-2001-33 with Washington Universities ftpd was not due to errors in glibc glob - but their own implementation of this function.

Previous discussions on bugtraq and other mailing lists ruled this bug as not exploitable. This is not entirely true. Global Intersec has since discovered a condition under which the bug may be used to exploit this vulnerability.

This is dependant on the program in question using the globfree() function, also defined in glibc glob.c (sysdeps/generic/glob.c). An example of this would be the OpenBSD ftpd Linux port. By carefully crafting user input to such daemons it is possible to corrupt memory space of the process. Ultimately the result of this would be an ability to execute arbitrary commands with the privileges of the server process. This is often root(0).

Scope for attack:

For this bug to be exploitable the attacker must be able to cause a daemon to call glob matching functions via services which allow either anonymous/public access or which may require authentication. This includes ftp daemons.

Work around:

The scope for your systems being targeted to this form of attack can be reduced by disabling remotely accessible daemons which use the functions in question. These include the OpenBSD ftpd Linux port. It is also suggested that removal of any public access to such daemons is removed until vendor fixes have been applied.


The glob bug was originally bought to light on several mailing lists, but was ruled out as not being exploitable. These include posts by flaviovs@magnux.com who later concluded the bug was exploitable.

Tom Parker from Global InterSec has discovered ways in which these bugs can be exploited when used in conjunction with globfree().

Many thanks go to SuSE GmbH who have worked with GIS to release the information described in this advisory on a mutually appropriate date.

Vendor Solutions:

Red Hat have released the following series of packages which fix the glibc issues. Other vendors are yet to release official packages due to a lack of preparation time. As vendors release their own updates, this document will be updated and can be viewed at the "Reference" location posted at the top of this document.

Red Hat Linux 6.2:

SRPMS: ftp://updates.redhat.com/6.2/en/os/SRPMS/glibc-2.1.3-23.src.rpm

alpha: ftp://updates.redhat.com/6.2/en/os/alpha/glibc-2.1.3-23.alpha.rpm ftp://updates.redhat.com/6.2/en/os/alpha/glibc-devel-2.1.3-23.alpha.rpm ftp://updates.redhat.com/6.2/en/os/alpha/glibc-profile-2.1.3-23.alpha.rpm ftp://updates.redhat.com/6.2/en/os/alpha/nscd-2.1.3-23.alpha.rpm

i386: ftp://updates.redhat.com/6.2/en/os/i386/glibc-2.1.3-23.i386.rpm ftp://updates.redhat.com/6.2/en/os/i386/glibc-devel-2.1.3-23.i386.rpm ftp://updates.redhat.com/6.2/en/os/i386/glibc-profile-2.1.3-23.i386.rpm ftp://updates.redhat.com/6.2/en/os/i386/nscd-2.1.3-23.i386.rpm

sparc: ftp://updates.redhat.com/6.2/en/os/sparc/glibc-2.1.3-23.sparc.rpm ftp://updates.redhat.com/6.2/en/os/sparc/glibc-devel-2.1.3-23.sparc.rpm ftp://updates.redhat.com/6.2/en/os/sparc/glibc-profile-2.1.3-23.sparc.rpm ftp://updates.redhat.com/6.2/en/os/sparc/nscd-2.1.3-23.sparc.rpm

sparcv9: ftp://updates.redhat.com/6.2/en/os/sparcv9/glibc-2.1.3-23.sparcv9.rpm

Red Hat Linux 7.0:

SRPMS: ftp://updates.redhat.com/7.0/en/os/SRPMS/glibc-2.2.4-

alpha: ftp://updates.redhat.com/7.0/en/os/alpha/glibc-2.2.4- ftp://updates.redhat.com/7.0/en/os/alpha/glibc-devel-2.2.4- m ftp://updates.redhat.com/7.0/en/os/alpha/glibc-profile-2.2.4- rpm ftp://updates.redhat.com/7.0/en/os/alpha/glibc-common-2.2.4- pm ftp://updates.redhat.com/7.0/en/os/alpha/nscd-2.2.4-

alphaev6: ftp://updates.redhat.com/7.0/en/os/alphaev6/glibc-2.2.4- m

i386: ftp://updates.redhat.com/7.0/en/os/i386/glibc-2.2.4- ftp://updates.redhat.com/7.0/en/os/i386/glibc-devel-2.2.4- ftp://updates.redhat.com/7.0/en/os/i386/glibc-profile-2.2.4- m ftp://updates.redhat.com/7.0/en/os/i386/glibc-common-2.2.4- ftp://updates.redhat.com/7.0/en/os/i386/nscd-2.2.4-

i686: ftp://updates.redhat.com/7.0/en/os/i686/glibc-2.2.4-

Red Hat Linux 7.1:

SRPMS: ftp://updates.redhat.com/7.1/en/os/SRPMS/glibc-2.2.4-19.3.src.rpm

alpha: ftp://updates.redhat.com/7.1/en/os/alpha/glibc-2.2.4-19.3.alpha.rpm ftp://updates.redhat.com/7.1/en/os/alpha/glibc-devel-2.2.4-19.3.alpha.rpm ftp://updates.redhat.com/7.1/en/os/alpha/glibc-profile-2.2.4-19.3.alpha.rpm ftp://updates.redhat.com/7.1/en/os/alpha/glibc-common-2.2.4-19.3.alpha.rpm ftp://updates.redhat.com/7.1/en/os/alpha/nscd-2.2.4-19.3.alpha.rpm

alphaev6: ftp://updates.redhat.com/7.1/en/os/alphaev6/glibc-2.2.4-19.3.alphaev6.rpm

i386: ftp://updates.redhat.com/7.1/en/os/i386/glibc-2.2.4-19.3.i386.rpm ftp://updates.redhat.com/7.1/en/os/i386/glibc-devel-2.2.4-19.3.i386.rpm ftp://updates.redhat.com/7.1/en/os/i386/glibc-profile-2.2.4-19.3.i386.rpm ftp://updates.redhat.com/7.1/en/os/i386/glibc-common-2.2.4-19.3.i386.rpm ftp://updates.redhat.com/7.1/en/os/i386/nscd-2.2.4-19.3.i386.rpm

i686: ftp://updates.redhat.com/7.1/en/os/i686/glibc-2.2.4-19.3.i686.rpm

ia64: ftp://updates.redhat.com/7.1/en/os/ia64/glibc-2.2.4-19.3.ia64.rpm ftp://updates.redhat.com/7.1/en/os/ia64/glibc-devel-2.2.4-19.3.ia64.rpm ftp://updates.redhat.com/7.1/en/os/ia64/glibc-profile-2.2.4-19.3.ia64.rpm ftp://updates.redhat.com/7.1/en/os/ia64/glibc-common-2.2.4-19.3.ia64.rpm ftp://updates.redhat.com/7.1/en/os/ia64/nscd-2.2.4-19.3.ia64.rpm

Red Hat Linux 7.2:

SRPMS: ftp://updates.redhat.com/7.2/en/os/SRPMS/glibc-2.2.4-19.3.src.rpm

i386: ftp://updates.redhat.com/7.2/en/os/i386/glibc-2.2.4-19.3.i386.rpm ftp://updates.redhat.com/7.2/en/os/i386/glibc-devel-2.2.4-19.3.i386.rpm ftp://updates.redhat.com/7.2/en/os/i386/glibc-profile-2.2.4-19.3.i386.rpm ftp://updates.redhat.com/7.2/en/os/i386/glibc-common-2.2.4-19.3.i386.rpm ftp://updates.redhat.com/7.2/en/os/i386/nscd-2.2.4-19.3.i386.rpm

i686: ftp://updates.redhat.com/7.2/en/os/i686/glibc-2.2.4-19.3.i686.rpm.

Exploits (Proof of concept):

For the purposes of proving a concept we will now refer to use of these functions in the OpenBSD ftp daemon - ported to Linux by David Madore.

As we have recently seen in the Washington University ftp daemon, free() based vulnerabilities are readily exploitable. In the case of the OpenBSD ftpd we must ensure that globfree() is called to make any use of the glob vulnerabilities.

Note: OpenBSD itself is not vulnerable to this form of
attack due to the way in which it handles memory pages.

By forcing globfree() to be called before the next_brace_sub condition occurs it is possible to control the address which is free()'d. In our first example we insert an invalid address onto the stack, causing the program to SEGV.

: 220 localhost FTP server (Version 6.5/OpenBSD, linux port 0.3.3) ready. -> USER ftp : 331 Guest login ok, type your name as password. Sleeping for 10 seconds... -> PASS AAAAAAAAAAAAAAAAAAA\xef\xef\xbe\xad\xde # ( <19 Bytes> <Addr to write> <Glob char>) : 230 Guest login ok, access restrictions apply. -> STAT ~AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA{

#0 0x400f7968 in globfree () at ../sysdeps/generic/glob.c:1055 #1 0x8051b0b in yyparse () at ftpcmd.y:1138 # 2 0x804b455 in main (argc=3D1094795585, argv=3D0xbffff864, envp=3D0xbffff86c) at ftpd.c:715

Examination of the registers shows that we have successfully inserted the intended address. As the address is not valid the ftp daemon seg faults.

<snip> esi 0xdeadbeef -559038737 edi 0xdeadbeef -559038737 </snip>

On giving the ftp daemon a valid address to free (In this case a pointer to syslog()) the daemon will continue to free() the address we gave it # where it again will segfault due to the address we gave it not being a valid malloc chunk.

#0 0x400c6178 in free () at malloc.c:2952 #1 0x400f7989 in globfree () at ../sysdeps/generic/glob.c:1055 #2 0x8051b0b in yyparse () at ftpcmd.y:1138 #3 0x804b455 in main (argc=3D1094795585, argv=3D0xbffff864, envp=3D0xbffff86c) at ftpd.c:715

ie (SuSE glibc-2.2/sysdeps/generic/glob.c): glob.c:1097 if (pglob->gl_pathv[pglob->gl_offs + i] != NULL) glob.c:1098 free ((__ptr_t) pglob->gl_pathv[pglob->gl_offs + i]); glob.c:1099 free ((__ptr_t) pglob->gl_pathv);

Information on exploiting this form of vulnerability are available at http://www.phrack.org/show.php?p=57&a=9

Legal: This advisory is the intellectual property of Global InterSec LLC but may be freely distributed with the conditions that: a) no fee is charged and b) appropriate credit is given. (c) Global InterSec LLC 2001