[Snort-sigs] SID 1497 documentation
kevin.peuhkurinen at ...1555...
Mon Jun 9 06:38:13 EDT 2003
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alert tcp $EXTERNAL_NET any -> $HTTP_SERVERS $HTTP_PORTS (msg:"WEB-MISC
cross site scripting attempt"; flow:to_server,established;
content:"<SCRIPT>"; nocase; classtype:web-application-attack; sid:1497;
A cross-site scripting attack is being attempted, or a potential
attacker is testing your site to determine if it is vulnerable.
Successful cross-site scripting attacks generally target the users of
your web site. Attackers can
potentially gain access to your users' cookies or session ids, allowing
the attacker to impersonate your
user. They could also set up elaborate fake logon screens to steal
user names and passwords.
Whenever a web application accepts input (either via the URL or via the
POST method) and then uses that input as part of the HTML of a new page
without filtering, the application is vulnerable to cross-site
scripting. The traditional means of exploiting this is to embed a
"<SCRIPT>" tag into the input. The code following the tag is then
executed by the victim's browser.
Many older versions of web server software are affected, as are numerous
The most common avenue of attack is for the attacker to send an HTML
formatted email to the victim. The
email will contain a link to a specially crafted URL which contains the
exploit. When the victim clicks on
the link, they are directed to the vulnerable web site and the attack
code is executed by their browser.
Ease of Attack:
Moderately Easy. Exploit code exists to automate attacks against users
of some widely deployed web
applications which are known to be vulnerable. Finding vulnerabilities
in other, including proprietary, web
applications is fairly trivial and existing exploit code could easily be
modified to take advantage of newly
Web pages that legimately include the <SCRIPT> tag could trigger this
alert under certain circumstances.
None known, although it is theoretically possible to obfuscate the
exploit code in a manner that Snort cannot
Determine if your web application is actually vulnerable to this
attack. If it is and the application is
not of your own design, contact the authors or vendor and see if there
is a patch or newer version. If the
application is proprietary to you or your company, ensure that it
properly validates input.
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