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Subject: CERT Advisory CA-2003-06 Multiple vulnerabilities in implementations of the
From: CERT Advisory <This email address is being protected from spambots. You need JavaScript enabled to view it.>
Date: Fri, 21 Feb 2003 10:24:08 -0500


CERT Advisory CA-2003-06 Multiple vulnerabilities in implementations of the
Session Initiation Protocol (SIP)

   Original release date: February 21, 2003
   Last revised: --
   Source: CERT/CC

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

Systems Affected

   SIP-enabled  products  from  a  wide  variety of vendors are affected.
   Other  systems  making  use of SIP may also be vulnerable but were not
   specifically  tested.  Not  all  SIP implementations are affected. See
   Vendor Information for details from vendors who have provided feedback
   for this advisory.

   In  addition to the vendors who provided feedback for this advisory, a
   list  of  vendors  whom  CERT/CC contacted regarding these problems is
   available from VU#528719.


   Numerous  vulnerabilities  have  been  reported  in  multiple vendors'
   implementations    of   the   Session   Initiation   Protocol.   These
   vulnerabilities  may allow an attacker to gain unauthorized privileged
   access,  cause  denial-of-service  attacks,  or  cause unstable system
   behavior.  If your site uses SIP-enabled products in any capacity, the
   CERT/CC  encourages  you  to  read this advisory and follow the advice
   provided in the Solution section below.

I. Description

   The  Session  Initiation  Protocol  (SIP)  is  a  developing and newly
   deployed  protocol  that  is  commonly  used  in Voice over IP (VoIP),
   Internet telephony, instant messaging, and various other applications.
   SIP  is  a  text-based  protocol for initiating communication and data
   sessions between users.

   The  Oulu  University  Secure  Programming  Group  (OUSPG)  previously
   conducted  research  into vulnerabilities in LDAP, culminating in CERT
   Advisory CA-2001-18, and SNMP, resulting in CERT Advisory CA-2002-03.

   OUSPG's most recent research focused on a subset of SIP related to the
   INVITE message, which SIP agents and proxies are required to accept in
   order to set up sessions. By applying the PROTOS c07-sip test suite to
   a  variety  of  popular  SIP-enabled  products,  the  OUSPG discovered
   impacts ranging from unexpected system behavior and denial of services
   to  remote  code  execution.  Note  that  "throttling"  is an expected

   Specifications  for  the  Session Initiation Protocol are available in

   OUSPG  has  established the following site with detailed documentation
   regarding SIP and the implementation test results from the test suite:

   The IETF Charter page for SIP is available at

II. Impact

   Exploitation  of these vulnerabilities may result in denial-of-service
   conditions,  service  interruptions,  and  in  some cases may allow an
   attacker  to gain unauthorized access to the affected device. Specific
   impacts will vary from product to product.

III. Solution

   Many  of  the  mitigation steps recommended below may have significant
   impact   on   your   everyday   network   operations   and/or  network
   architecture.  Ensure  that  any  changes  made based on the following
   recommendations  will  not  unacceptably  affect  your ongoing network
   operations capability.

  Apply a patch from your vendor

     Appendix  A  contains  information  provided  by  vendors  for this
     advisory.  Please  consult this appendix and VU#528719 to determine
     if  your  product is vulnerable. If a statement is unavailable, you
     may need to contact your vendor directly.

  Disable the SIP-enabled devices and services

     As  a general rule, the CERT/CC recommends disabling any service or
     capability  that  is  not explicitly required. Some of the affected
     products  may  rely  on  SIP to be functional. You should carefully
     consider the impact of blocking services that you may be using.

  Ingress filtering

     As  a  temporary  measure, it may be possible to limit the scope of
     these  vulnerabilities  by  blocking  access  to  SIP  devices  and
     services at the network perimeter.

     Ingress  filtering  manages  the  flow  of  traffic  as it enters a
     network  under  your  administrative control. Servers are typically
     the  only  machines  that  need  to accept inbound traffic from the
     public  Internet.  Note  that  most  SIP  User Agents (including IP
     phones  or  "clien"t software) consist of a User Agent Client and a
     User Agent Server. In the network usage policy of many sites, there
     are  few  reasons for external hosts to initiate inbound traffic to
     machines  that  provide no public services. Thus, ingress filtering
     should  be performed at the border to prohibit externally initiated
     inbound  traffic  to  non-authorized  services.  For  SIP,  ingress
     filtering  of  the following ports can prevent attackers outside of
     your network from accessing vulnerable devices in the local network
     that are not explicitly authorized to provide public SIP services:

     sip     5060/udp     # Session Initiation Protocol (SIP)
     sip     5060/tcp     # Session Initiation Protocol (SIP)
     sip     5061/tcp     # Session Initiation Protocol (SIP) over TLS

     Careful  consideration  should  be  given to addresses of the types
     mentioned  above  by sites planning for packet filtering as part of
     their mitigation strategy for these vulnerabilities.

     Please note that this workaround may not protect vulnerable devices
     from internal attacks.

  Egress filtering

     Egress filtering manages the flow of traffic as it leaves a network
     under  your administrative control. There is typically limited need
     for machines providing public services to initiate outbound traffic
     to  the Internet. In the case of the SIP vulnerabilities, employing
     egress  filtering  on the ports listed above at your network border
     may prevent your network from being used as a source for attacks on
     other sites.

  Block SIP requests directed to broadcast addresses at your router.

     Since  SIP  requests  can be transmitted via UDP, broadcast attacks
     are  possible. One solution to prevent your site from being used as
     an  intermediary  in an attack is to block SIP requests directed to
     broadcast addresses at your router.

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

  America Online Inc

     Not vulnerable.

  Apple Computer Inc.

     There  are currently no applications shipped by Apple with Mac OS X
     or  Mac  OS  X  Server  which  make  use  of the Session Initiation


     No  BorderWare  products  make  use  of  SIP and thus no BorderWare
     products are affected by this vulnerability.


     No  Clavister  products  currently  incorporate support for the SIP
     protocol suite, and as such, are not vulnerable.
     We  would  however like to extend our thanks to the OUSPG for their
     work  as  well  as  for the responsible manner in which they handle
     their  discoveries.  Their  detailed  reports  and  test suites are
     certainly well-received.
     We  would  also  like  to  reiterate  the  fact that SIP has yet to
     mature,  protocol-wise  as  well  as implementation-wise. We do not
     recommend  that  our customers set up SIP relays in parallel to our
     firewall  products  to  pass  SIP-based  applications  in or out of
     networks where security is a concern of note.

  F5 Networks

     F5  Networks  does  not have a SIP server product, and is therefore
     not affected by this vulnerability.


     With  regards  to VU#528719, Fujitsu's UXP/V o.s. is not vulnerable
     because the relevant function is not supported under UXP/V.


     SIP is not implemented as part of the AIX operating system.

  IP Filter

     IPFilter  does  not  do  any  SIP specific protocol handling and is
     therefore not affected by the issues mentioned in the paper cited.


     All versions of SIP Express Router up to 0.8.9 are sadly vulnerable
     to  the  OUSPG test suite. We strongly advice to upgrade to version
     0.8.10.  Please  also  apply  the  patch  to  version  0.8.10  from
     before  installation  and keep on watching this site in the future.
     We apologize to our users for the trouble.

  Hewlett-Packard Company

     Hewlett-Packard Company
     Software Security Response Team
     cross reference id: SSRT2402

     HP-UX - not vulnerable
     HP-MPE/ix - not vulnerable
     HP Tru64 UNIX - not vulnerable
     HP OpenVMS - not vulnerable
     HP NonStop Servers - not vulnerable

     To  report  potential security vulnerabilities in HP software, send
     an E-mail message to: This email address is being protected from spambots. You need JavaScript enabled to view it.


     No  Lucent products are known to be affected by this vulnerability,
     however  we  are  still  researching the issue and will update this
     statement as needed.

  Microsoft Corporation

     Microsoft  has  investigated these issues. The Microsoft SIP client
     implementation is not affected.

  NEC Corporation

     NEC vendor statement for VU#528719

     sent on February 13, 2002
     Server Products
       * EWS/UP 48 Series operating system
       * - is NOT vulnerable, because it does not support SIP.

     Router Products
       * IX 1000 / 2000 / 5000 Series
       * - is NOT vulnerable, because it does not support SIP.

     Other Network products
       * We continue to check our products which support SIP protocol.



     NetBSD does not ship any implementation of SIP.

     As  the  linux  2.4/2.5  netfilter implementation currently doesn't
     support  connection  tracking or NAT for the SIP protocol suite, we
     are not vulnerable to this bug.


     NetScreen is not vulnerable to this issue.

  Network Appliance

     NetApp products are not affected by this vulnerability.


     Nokia  IP  Security  Platforms  based  on  IPSO, Nokis Small Office
     Solution  platforms, Nokia VPN products and Nokia Message Protector
     platform  do  not  initiate  or  terminate  SIP based sessions. The
     mentioned Nokia products are not susceptible to this vulnerability

  Nortel Networks

     Nortel  Networks is cooperating to the fullest extent with the CERT
     Coordination  Center. All Nortel Networks products that use Session
     Initiation  Protocol  SIP)  have  been  tested  and  all  generally
     available  products, with the following exceptions, have passed the
     test suite:

     Succession  Communication  Server 2000 and Succession Communication
     Server  2000  -  Compact  are  impacted  by  the test suite only in
     configurations   where   SIP-T  has  been  provisioned  within  the
     Communication  Server; a software patch is expected to be available
     by the end of February.

     For  further  information  about  Nortel  Networks  products please
     contact Nortel Networks Global Network Support.

     North America: 1-800-4-NORTEL, or (1-800-466-7835)
     Europe,  Middle  East & Africa: 00800 8008 9009, or +44 (0) 870 907

     Contacts   for  other  regions  available  at  the  Global  Contact
     <> web page.


     Novell has no products implementing SIP.

  Secure Computing Corporation

     Neither  Sidewinder  nor Gauntlet implements SIP, so we do not need
     to be on the vendor list for this vulnerability.


     We  hereby attest that SecureWorx Basilisk Gateway Security product
     suite  (Firmware  version  3.4.2 or later) is NOT VULNERABLE to the
     Session   Initiation  Protocol  (SIP)  Vulnerability  VU#528719  as
     described in the OUSPG announcement (OUSPG#0106) received on Fri, 8
     Nov 2002 10:17:11 -0500.


     Stonesoft's  StoneGate  high  availability firewall and VPN product
     does not contain any code that handles SIP protocol. No versions of
     StoneGate are vulnerable.


     Symantec  Corporation  products  are  not vulnerable to this issue.
     Symantec  does  not implement the Session Initiation Protocol (SIP)
     in any of our products.


     Xerox is aware of this vulnerability and is currently assessing all
     products. This statement will be updated as new information becomes

Appendix B. - References

    5. RFC3261 - SIP: Session Initiation Protocol
    6. RFC2327 - SDP: Session Description Protocol
    7. RFC2279 - UTF-8, a transformation format of ISO 10646
    8. Session Initiation Protocol Basic Call Flow Examples 
    9. Session Initiation Protocol Torture Test Messages, Draft 

   The  CERT  Coordination  Center  thanks  the  Oulu  University  Secure
   Programming  Group  for  reporting  these  vulnerabilities  to us, for
   providing  detailed  technical  analysis,  and  for  assisting  us  in
   preparing  this  advisory.  We  would  also  like  to  acknowledge the
   "RedSkins"  project  of  "MediaTeam  Oulu"  for  their support of this

   Feedback  on  this  document  can be directed to the authors, 
   Jason A. Rafail and Ian A. Finlay.

   This document is available from:

CERT/CC Contact Information

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          Fax: +1 412-268-6989
          Postal address:
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          Carnegie Mellon University
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   Revision History
      Feb 21, 2003: Initial release

Version: PGP 6.5.8


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