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[Advisory][Unix] Buffer Overflow in FTP-Servern verschiedener Hersteller - CA-2001-07



[[PGP Signed Part:Undecided]]
Liebe Kolleginnen und Kollegen,

soeben erreichte uns das nachfolgende Advisory des CERT Coordination
Centers. Wir geben diese Informationen unveraendert an Sie weiter.

Beschrieben wird eine Schwachstelle im Buffer Handling verschiedener
FTP-Server, die es einem Angreifer ueber das Netz ermoeglichen
koennte, beliebigen Programmcode auf dem Server unter der Benutzer-ID
des FTP-Daemons zu starten.

Die Schwachstelle steht im Zusammenhang mit der
"Globbing"-Funktionalitaet, mit der Unix-Shells und auch viele
FTP-Server regulaere Ausdruecke und Abkuerzungen in komplette
Dateinamen aufloesen. So wird beispielsweise der Ausdruck "~foo/datei"
in den kompletten Pfad zum Heimatverzeichnis des Benutzers "foo"
aufgeloest. Mit "mget *.txt" werden alle Dateien im aktuellen
Verzeichnis mit der Endung ".txt" heruntergeladen und mit "ls *.c"
alle Dateien mit der Endung ".c" angezeigt.

Diese Schwachstelle darf nicht verwechselt werden mit der von PGP
Security entdeckten Schwachstelle, die eine Denial of Service Attacke
ermoeglicht und ebenfalls mit der "Globbing" Funktionalitaet in
Zusammenhang steht. Siehe

	http://www.pgp.com/research/covert/advisories/048.asp

Einen allgemeinen Workaround gibt es nicht. CERT/CC raet, Updates
einzuspielen, sobald der Hersteller sie zur Verfuegung stellt.

Derzeit liegen Meldungen vor von

Compaq Computer Corporation
Compaq arbeitet zur Zeit an einem Update.

FreeBSD, Inc.
Der Fehler ist behoben in FreeBSD 5.0-CURRENT und FreeBSD 4.2-STABLE,
und wird in FreeBSD 4.3-RELEASE nicht mehr enthalten sein.

Fujitsu
Der Hersteller arbeitet derzeit an einem Update.

IBM Corporation
Nach Aussagen von IBM ist die "glob()" Funktion im AIX FTP-Daemon von
der Schwachstelle nicht betroffen.

NetBSD
Fuer 4.4BSD gibt es bereits seit Ende Maerz einen Bugfix fuer beide
Schwachstellen, die mit "glob()" in Verbindung stehen.

SGI
Der Hersteller untersucht derzeit sein Produkt auf die genannte
Schwachstelle.

Mit freundlichen Gruessen,
	Marco Thorbruegge, DFN-CERT
-- 
Marco Thorbruegge        |              mailto:thorbruegge@cert.dfn.de
DFN-CERT GmbH            |          http://www.cert.dfn.de/team/matho/
Oberstrasse 14b          |                    Phone: +49(40)808077-555
D-20144 Hamburg          |                      FAX: +49(40)808077-556
Germany                  | PGP-Key: finger thorbruegge@ftp.cert.dfn.de

CERT Advisory CA-2001-07 File Globbing Vulnerabilities in Various FTP
Servers

   Original release date: April 10, 2001
   Last revised: --
   Source: CERT/CC

   A complete revision history can be found at the end of this file.

Systems Affected

   FTP servers on various platforms

Overview

   A variety of FTP servers incorrectly manage buffers in a way that can
   lead to remote intruders executing arbitrary code on the FTP server.
   The incorrect management of buffers is centered around the return from
   the glob() function, and may be confused with a related
   denial-of-service problem. These problems were discovered by the
   COVERT Labs at PGP Security.

I. Description

   Filename "globbing" is the process of expanding short-hand notation
   into complete file names. For example, the expression "*.c" (without
   the quotes) is short-hand notation for "all files ending in ".c"
   (again, without the quotes). This is commonly used in UNIX shells, in
   commands such as ls *.c. Globbing also often includes the expansion of
   certain characters into system-specific paths, such as the expansion
   of tilde character (~) into the path of the home directory of the user
   specified to the right of the tilde character. For example, "~foo"
   expands to the home directory for the user "foo" on the current
   system. The expressions used in filename globbing are not strictly
   regular expressions, but they are syntactically similar in many ways.

   Many FTP servers also implement globbing, so that the command mget *.c
   means retrieve all the files ending in ".c," and get ~foo/file.name
   means get the file named "file.name" in the home directory of foo.

   The COVERT Labs at PGP Security have discovered a means to use the
   expansion done by the glob function to overflow various buffers in FTP
   servers, allowing an intruder to execute arbitrary code. For more
   details about their discovery, see

          http://www.pgp.com/research/covert/advisories/048.asp

   Quoting from that document:

          [...] when an FTP daemon receives a request involving a file
          that has a tilde as its first character, it typically runs the
          entire filename string through globbing code in order to
          resolve the specified home directory into a full path. This has
          the side effect of expanding other metacharacters in the
          pathname string, which can lead to very large input strings
          being passed into the main command processing routines. This
          can lead to exploitable buffer overflow conditions, depending
          upon how these routines manipulate their input.

   For the latest information regarding this vulnerability, including
   information related to vendors' exposure to this problem, consult the
   vulnerability note describing this problem, available at

          http://www.kb.cert.org/vuls/id/808552

II. Impact

   Intruders can execute arbitrary code with the permissions of the
   process running the FTP server.

III. Solution

   Apply a patch or workaround from your vendor, as described in Appendix
   A.

Appendix A. - Vendor Information

   This appendix contains information provided by vendors for this
   advisory. When vendors report new information to the CERT/CC, we
   update this section and note the changes in our revision history. If a
   particular vendor is not listed below, we have not received their
   comments.

Compaq Computer Corporation

   COMPAQ COMPUTER CORPORATION

   -----------------------------
   x-ref: J Compaq case id - SSRT1-83

   At the time of writing this document, Compaq is currently
   investigating the potential impact to Compaq's ftp service.

   Initial tests indicate Compaq's ftp service is not vulnerable.

   As further information becomes available Compaq will provide notice of
   the completion/availibility of any necessary patches through AES
   services (DIA,DSNlink FLASH and posted to the Services WEB page) and
   be available from your normal Compaq Services Support channel.

   COMPAQ COMPUTER CORPORATION

FreeBSD, Inc.

   FreeBSD is vulnerable to the glob-related bugs. We have corrected
   these bugs in FreeBSD 5.0-CURRENT and FreeBSD 4.2-STABLE, and they
   will not be present in FreeBSD 4.3-RELEASE.

Fujitsu

   [...] we have determined that the versions of UXP/V shown below are
   vulnerable. JPatches are being prepared and will be assigned the patch
   numbers also shown below:

   OS Version,PTF level patch ID
   -------------------- --------
   UXP/V V20L10 X01021  UX28161
   UXP/V V20L10 X00091  UX28160
   UXP/V V10L20 X01041  UX15527

IBM Corporation

   [...] we have not found the described vulnerabilities to exist in the
   AIX versions of glob as used in the ftp daemon.

NetBSD

   Please be aware that as of March 29, 2001, NetBSD has a fix for both
   the glob resource consumption (via an application controlled
   GLOB_LIMIT flag) and the buffer overflow (always enforced). These
   fixes should work on any 4.4BSD derived glob(3).

SGI

   SGI acknowledges the vulnerability reported by NAI COVERT Labs and is
   currently investigating. No further information is available at this
   time.

   As further information becomes available, additional advisories will
   be issued via the normal SGI security information distribution methods
   including the wiretap mailing list and
   http://www.sgi.com/support/security/

   For the protection of all our customers, SGI does not disclose,
   discuss or confirm vulnerabilities until a full investigation has
   occurred and any necessary patch(es) or release streams are available
   for all vulnerable and supported IRIX operating systems.

   Until SGI has more definitive information to provide, customers are
   encouraged to assume all security vulnerabilities as exploitable and
   take appropriate steps according to local site security policies and
   requirements.
     _________________________________________________________________

   The CERT Coordination Center would like to thank the COVERT Labs at
   PGP Security for notifying us about this problem and for their help in
   constructing this advisory.
     _________________________________________________________________

   Author: Shawn V. Hernan
   ______________________________________________________________________

   This document is available from:
   http://www.cert.org/advisories/CA-2001-07.html
   ______________________________________________________________________

CERT/CC Contact Information

   Email: cert@cert.org
          Phone: +1 412-268-7090 (24-hour hotline)
          Fax: +1 412-268-6989
          Postal address:
          CERT Coordination Center
          Software Engineering Institute
          Carnegie Mellon University
          Pittsburgh PA 15213-3890
          U.S.A.

   CERT personnel answer the hotline 08:00-20:00 EST(GMT-5) / EDT(GMT-4)
   Monday through Friday; they are on call for emergencies during other
   hours, on U.S. holidays, and on weekends.

Using encryption

   We strongly urge you to encrypt sensitive information sent by email.
   Our public PGP key is available from

   http://www.cert.org/CERT_PGP.key

   If you prefer to use DES, please call the CERT hotline for more
   information.

Getting security information

   CERT publications and other security information are available from
   our web site

   http://www.cert.org/

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   * "CERT" and "CERT Coordination Center" are registered in the U.S.
   Patent and Trademark Office.
   ______________________________________________________________________

   NO WARRANTY
   Any material furnished by Carnegie Mellon University and the Software
   Engineering Institute is furnished on an "as is" basis. Carnegie
   Mellon University makes no warranties of any kind, either expressed or
   implied as to any matter including, but not limited to, warranty of
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     _________________________________________________________________

   Conditions for use, disclaimers, and sponsorship information

   Copyright 2001 Carnegie Mellon University.

   Revision History
April 10, 2001:  Initial release


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