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CERT Advisory CA-2001-33 Multiple Vulnerabilities in WU-FTPD
From: CERT Advisory <cert-advisory () cert org>
Date: Thu, 29 Nov 2001 18:47:23 -0500 (EST)


CERT Advisory CA-2001-33 Multiple Vulnerabilities in WU-FTPD

   Original release date: November 29, 2001
   Last revised: --
   Source: CERT/CC

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

Systems Affected

     * Systems running WU-FTPD and its derivatives


   WU-FTPD  is  a  widely  deployed software package used to provide File
   Transport Protocol (FTP) services on UNIX and Linux systems. There are
   two  vulnerabilities  in  WU-FTPD  that  expose  a system to potential
   remote root compromise by anyone with access to the FTP service. These
   vulnerabilities have recently received increased scrutiny.

I. Description

   There  are two remote code execution vulnerabilities in the Washington
   University  FTP  daemon  (WU-FTPD). Both of these vulnerabilities have
   been discussed in public forums and have received widespread exposure.

   VU#886083: WU-FTPD does not properly handle glob command

   WU-FTPD  features  globbing  capabilities that allow a user to specify
   multiple  file  names  and locations using typical shell notation. See
   CERT Advisory CA-2001-07 for a more complete explanation of globbing.

   WU-FTPD implements its own globbing code instead of using libraries in
   the  underlying operating system. When the globbing code is called, it
   allocates  memory on the heap to store a list of file names that match
   the  expanded  glob  expression.  The  globbing  code  is  designed to
   recognize  invalid syntax and return an error condition to the calling
   function.  However, when it encounters a specific string, the globbing
   code  fails  to  properly  return  the error condition. Therefore, the
   calling function proceeds as if the glob syntax were correct and later
   frees unallocated memory that can contain user-supplied data.
   If  intruders can place addresses and shellcode in the right locations
   on  the  heap using FTP commands, they may be able to cause WU-FTPD to
   execute  arbitrary  code by later issuing a command that is mishandled
   by the globbing code.

   This  vulnerability is potentially exploitable by any user who is able
   to  log  in  to  a  vulnerable  server, including users with anonymous
   access.  If  the  exploit  is  successful,  an attacker may be able to
   execute arbitrary code with the privileges of WU-FTPD, typically root.
   If  the exploit is unsuccessful, the thread servicing the request will
   fail, but the WU-FTPD process will continue to run.

   This  vulnerability  has been assigned the identifier CAN-2001-0550 by
   the Common Vulnerabilities and Exposures (CVE) group:


   CORE  Security  Technologies  has  published a Vulnerability Report on
   this issue:


   VU#639760: WU-FTPD configured to use RFC 931 authentication running in
   debug mode contains format string vulnerability

   WU-FTPD  can  perform  RFC  931  authentication when accepting inbound
   connections  from  clients.  RFC 931 defines the Authentication Server
   Protocol,  and  is  obsoleted  by  RFC 1413 which defines the Identity
   Protocol. RFC 931 is commonly known as "auth" or "authd", and RFC 1413
   is commonly known "ident" or "identd". Both are named after the daemon
   that commonly provides the service.

   When   using  RFC  931  authentication,  WU-FTPD  will  request  ident
   information before authorizing a connection request from a client. The
   auth  or  ident  service  running  on the client returns user-specific
   information,  allowing  WU-FTPD to make authentication decisions based
   on data in the ident response.

   WU-FTPD  can  also  be  run in debugging mode, which provides detailed
   information about its operation.

   When  WU-FTPD  is  configured to perform RFC 931 authentication and is
   run  in  debug  mode,  it  logs connection information using syslog(3)
   function  calls.  The  logging  code  does  not  include format string
   specifiers in some syslog(3) calls, nor does the code perform adequate
   input  validation on the contents of the identd response received from
   a   client.   As  a  result,  a  crafted  identd  response  containing
   user-supplied  format  string  specifiers is interpreted by syslog(3),
   possibly  overwriting  arbitrary  locations  in  memory.  By carefully
   designing  such a request, an attacker may execute arbitrary code with
   the privileges of WU-FTPD.

   This  vulnerability is potentially exploitable by any user who is able
   to  log  in  to  a  vulnerable  server, including users with anonymous
   access.  The  intruder  must also be able to control their response to
   the  ident  request. If successful, an attacker may be able to execute
   arbitrary code with the privileges of WU-FTPD, typically root.

   Note  that  this  vulnerability  does  not  manifest unless WU-FTPD is
   configured to use RFC 931 authentication and is run in debug mode.

   This  vulnerability  has been assigned the identifier CAN-2001-0187 by
   the Common Vulnerabilities and Exposures (CVE) group:


II. Impact

   Both  of  these  vulnerabilities can be exploited remotely by any user
   with  access  to  the  FTP  service,  including anonymous access. Both
   vulnerabilities  allow  an intruder to execute arbitrary code with the
   privileges  of  WU-FTPD,  typically root. An exploit attempt that does
   not  succeed in executing code may crash WU-FTPD or end the connection
   used by the intruder.

   For  additional  information  about  the  impacts  of  each  of  these
   vulnerabilities,  please consult the CERT Vulnerability Notes Database

III. Solution

Apply patches from your vendor

   Appendix A contains information for this advisory provided by vendors.
   As  they  report  new  information to the CERT/CC, we will 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.
   Please contact your vendor directly.

Restrict access to WU-FTPD

   As  a  general practice, the CERT/CC recommends disabling services and
   access  that  are  not  explicitly  required.  You may wish to disable
   WU-FTPD until you are able to apply a patch.

   If  you  cannot  disable  the  service, you can limit your exposure to
   these vulnerabilities by blocking or restricting access to the control
   channel  (by default, port 21/tcp) used by WU-FTPD. In the case of the
   format   string   vulnerability   (VU#639760),  an  exploit  would  be
   transmitted  from  port  113/tcp  on the attacking host to the WU-FTPD
   server  that  made  the identd request. Note that blocking access from
   untrusted  networks such as the Internet does not protect your systems
   against attacks from within your network.

Disable anonymous FTP access

   Although  disabling anonymous FTP access does not prevent attacks from
   occurring,  it  does  prevent unauthenticated users from attempting to
   exploit the globbing vulnerability (VU#886083).

Appendix A. Vendor Information

   This  appendix  contains  information  provided  by  vendors  for this
   advisory.  As  vendors  report new information to the CERT/CC, we will
   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.   Note   that   this   advisory   discusses   two   distinct
   vulnerabilities, and vendor statements may address one or both.


   Caldera has released Security Advisory CSSA-2001-041.0:



   Cray,  Inc.  is  not vulnerable since the ftp supplied with UNICOS and
   UNICOS/mk  is not based on the Washington University version. Cray did
   check their ftp code and does not see this exploit.


   Debian  addressed  VU#639760  with Debian Security Advisory DSA-016 in
   January 2001:


Hewlett-Packard Company

   HP's  HP-UX  is immune to this issue. It was fixed in conjunction with
   the  last  "globbing"  issue  announced  in  CERT Advisory CA-2001-07,
   released  April  10,  2001.  The  lab did a complete check/scan of the
   globbing software, and fixed this issue then as well. Customers should
   apply  the  patches  listed in HP Security Bulletin #162 released July

          HPSBUX0107-162 Security Vulnerability in ftpd and ftp

   Hewlett-Packard  Security  Bulletins  are available at the IT Resource
   Center web site (registration required):


IBM Corporation

   IBM's  AIX  operating  system  does  not  use  WU-FTPD,  hence  is not
   vulnerable to the exploit described by CORE ST.


   Immunix has released Security Advisory IMNX-2001-70-036-01:



   OpenBSD does not use WU-FTPD.

RedHat Inc.

   RedHat has released Errata Advisory RHSA-2001-147:



   SGI  does  not  ship  IRIX  with wu-ftpd, so IRIX is not vulnerable to
   these issues.


   SuSE has released SuSE Security Announcement SuSE-SA:2001:043.


   The  WU-FTPD  Development  Group has provided source code patches that
   address both of these issues.
     * VU#886083:
     * VU#639760:

   The CERT Coordination Center thanks CORE Security Technologies and the
   WU-FTPD Development Group for their help

   Author: Art Manion

     * http://www.kb.cert.org/vuls/id/886083
     * http://www.kb.cert.org/vuls/id/639760
     * http://www.kb.cert.org/vuls
     * http://www.ietf.org/rfc/rfc931.txt
     * http://www.ietf.org/rfc/rfc1413.txt
     * http://www.ietf.org/rfc/rfc959.txt
     * http://www.corest.com/pressroom/advisories_desplegado.php?idxsecti

   This document is available from:

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

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   Revision History
November 29, 2001:  Initial release

Version: PGP 6.5.8


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