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From Christopher Schultz <ch...@christopherschultz.net>
Subject Re: Vulnerability from PCI scan
Date Tue, 01 Nov 2016 21:25:57 GMT
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Carl,

On 11/1/16 5:11 PM, Carl K. wrote:
> Control Scan has returned this as a vulnerability in Tomcat
> 8.0.38:
> 
> Vulnerable version of Apache Tomcat: 8.0.38
> 
> Risk: High (3) Port: 443/tcp Protocol: tcp Threat ID:
> web_dev_tomcatver
> 
> Details: 404 Error Page Cross Site Scripting Vulnerability 
> 12/21/09 Apache Tomcat is prone to a cross-site scripting
> vulnerability because it fails to properly sanitize user-supplied
> input. An attacker may leverage this issue to execute arbitrary
> script code in the browser of an unsuspecting user in the context
> of the affected site. Apache Tomcat mitigates HTTP_PROXY
> environment variable "httpoxy" issue
> 
> I have read everything I can find and it still doesn't make
> sense... can someone help to point me in the correct direction?
> 
> I am further puzzled because this is the first time this has come
> up and we run Tomcat for years... note that the date is listed as
> 12-21-2009.

Technically, this is not a vulnerability in Tomcat (or any
reverse-proxy, such as httpd) but it does represent a failure to
protect stupid command-line utilities from making bad decisions about
trusting environment variables.

Long story short, if using the CGI Servlet, any headers coming from
the request are set as HTTP_* environment variables on a script that
is executed as a CGI script. Notably, python, Perl, and PHP (and
others) use an environment variable called HTTP_PROXY to indicate the
presence of a forward-proxy to be used for outgoing HTTP connections.
Thus, setting a "Proxy" header in an HTTP request to Tomcat will
result in a CGI script seeing that value in the HTTP_PROXY environment
variable. This could present a problem in your environment, but is
possible to mitigate in a number of different ways.

https://www.apache.org/security/asf-httpoxy-response.txt

I have no idea where your scanner got the date 2009-12-21. Perhaps
they took the recently-disclosed CVE (CVE-2016-5388 -- note the year
on that CVE identifier) and made a best-guess of when the product was
first vulnerable. The first beta version of Tomcat 7 wasn't available
until 2010, so perhaps they were considering Tomcat 6 as well. But
Tomcat 6's history goes back well before that. Honestly, I think they
may have picked that date out of the air.

At any rate, you are safe if any of the following are true:

1. You don't use the CGI servlet
2. You don't use any scripts that use HTTP_PROXY in this manner
   (this is a weak criteria, since you may not KNOW if you are using
    such scripts)
3. You don't allow outgoing HTTP requests from your application servers,
   and no error messages produces by those scripts would leak any
   information like URLs, etc.
4. If you have a reverse-proxy (e.g. httpd) and explicitly remove any
   "proxy" headers from incoming HTTP requests

Mitigation is possible through a variety of means. If you aren't
vulnerable, this scan is likely to complain merely because of the
version number of Tomcat and the fact that this CVE hasn't officially
been closed, yet.

- -chris
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