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UNIRAS Brief - 404/03 - AUSCERT - Insecurity of Web-based Feedback Forms



 
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   UNIRAS (UK Govt CERT) Briefing Notice - 404/03 dated 15.07.03  Time: 10:25
 UNIRAS is part of NISCC(National Infrastructure Security Co-ordination Centre)
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  UNIRAS material is also available from its website at www.uniras.gov.uk and
         Information about NISCC is available from www.niscc.gov.uk
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Title
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AUSCERT Advisory:

Insecurity of Web-based Feedback Forms

Detail
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AA-2003.02                     AUSCERT Advisory

                  Insecurity of Web-based Feedback Forms
                               14 July 2003
Last Revised: --

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AusCERT has received information regarding potential vulnerabilities in the
implementation of some Web-based feedback forms.

This vulnerability may allow remote users to misuse these forms to send
Unsolicited Bulk Email (UBE).

This advisory will be updated as more information becomes available.

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1.  Description

    In order to obtain written feedback from their clients, many
    organisations implement web-based feedback forms. A common method for
    doing this is to use the FORM HTML element and the POST method option. 
    These forms often use email to send the results, with the destination
    email address configured using a hidden INPUT field. The CGI code which
    performs this function may be written "in house" or adapted from
    external sources (FormMail is a popular example).

    The following code snippet shows an example of the HTML tag used 
    (within the FORM tag) which may leave a web server open to abuse:

<FORM action="result-script" method="post">
...
<INPUT type=hidden name="recipient" value="feedback@xxxxxxxxxxxxxxxxx">
...
</FORM>


2.  Impact

    Without adequate server-side validation, it is possible for remote
    clients to make a form submission with an arbitrary destination email
    address. By allowing this, organisations inadvertently allow their
    servers to be used for sending UBE, via feedback forms. AusCERT has
    observed the exploitation of this weakness across the Internet.


3.  Workarounds/Mitigation

    Organisations who use feedback forms on their web sites should review
    their code and test the form submission to ensure proper server-side
    validation. Server-side CGI scripts should validate the domain of
    this email address or alternatively, hard-code the email address.

    If the feedback form is developed externally, then the vendor web site
    should be consulted for any updates or security information.

    Users of the popular FormMail CGI should upgrade to Version 1.91 or
    higher and make use of the "@recipients" array which allow
    specification of acceptable recipient email addresses or domains.

    There exists a related vulnerability in Allaire Forums which allows
    malicious users to impersonate other users using unverified hidden
    fields. See REFERENCES for more information.


REFERENCES: 

    http://www.stickysauce.com/tutorials/misc/spamproof.htm
    http://www.kb.cert.org/vuls/id/575619
    http://www.scriptarchive.com/formmail.html
    http://willmaster.com/master/feedback/

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AusCERT would like to acknowledge the assistance of Michael O'Brien, Senior
Security Consultant of LogicaCMG in producing this Advisory.
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AusCERT has made every effort to ensure that the information contained
in this document is accurate.  However, the decision to use the information
described is the responsibility of each user or organisation. The decision to
follow or act on information or advice contained in this security bulletin is
the responsibility of each user or organisation, and should be considered in
accordance with your organisation\'s site policies and procedures. AusCERT
takes no responsibility for consequences which may arise from following or
acting on information or advice contained in this security bulletin.

If you believe that your computer system has been compromised or attacked in 
any way, we encourage you to let us know by completing the secure National IT 
Incident Reporting Form at:

        http://www.auscert.org.au/render.html?it=3192

AusCERT also maintains a World Wide Web service which is found on:
http://www.auscert.org.au.

Internet Email: auscert@xxxxxxxxxxxxxx
Facsimile:      (07) 3365 7031
Telephone:      (07) 3365 4417 (International: +61 7 3365 4417)
                AusCERT personnel answer during Queensland business
                hours which are GMT+10:00 (AEST).  On call after hours
                for member emergencies only.

Postal:
Australian Computer Emergency Response Team
The University of Queensland
Brisbane
Qld  4072
AUSTRALIA


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Revision History


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For additional information or assistance, please contact the HELP Desk by 
telephone or Not Protectively Marked information may be sent via EMail to:
uniras@xxxxxxxxxxxx

Office Hours:
Mon - Fri: 08:30 - 17:00 Hrs
Tel: +44 (0) 20 7821 1330 Ext 4511
Fax: +44 (0) 20 7821 1686

Outside of Office Hours:
On Call Duty Officer:
Tel: +44 (0) 20 7821 1330 and follow the prompts

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UNIRAS wishes to acknowledge the contributions of AUSCERT for the information
contained in this Briefing. 
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This Briefing contains the information released by the original author. Some 
of the information may have changed since it was released. If the vulnerability 
affects you, it may be prudent to retrieve the advisory from the canonical site 
to ensure that you receive the most current information concerning that problem.

Reference to any specific commercial product, process, or service by trade 
name, trademark manufacturer, or otherwise, does not constitute or imply 
its endorsement, recommendation, or favouring by UNIRAS or NISCC.  The views 
and opinions of authors expressed within this notice shall not be used for 
advertising or product endorsement purposes.

Neither UNIRAS or NISCC shall also accept responsibility for any errors 
or omissions contained within this briefing notice. In particular, they shall 
not be liable for any loss or damage whatsoever, arising from or in connection 
with the usage of information contained within this notice.

UNIRAS is a member of the Forum of Incident Response and Security Teams (FIRST) 
and has contacts with other international Incident Response Teams (IRTs) in 
order to foster cooperation and coordination in incident prevention, to prompt 
rapid reaction to incidents, and to promote information sharing amongst its 
members and the community at large. 
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<End of UNIRAS Briefing>
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