A spammer is using my cgiemail, what do I do?
Cgiemail is a program developed by
folks over at MIT. It’s a CGI or server-side program designed to
accept input from an HTML form, process that input against a
template, and send the results as email. Recently, a
vulnerability has been discovered that allows spammers to use
cgiemail to send mail “through” the system on which cgiemail
resides. This results in increased and sometimes overwhelming
system load as well as the potential for spam to be sent in
your name.
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More details on the specifics of cgiemail’s vulnerability
can be found here on
SecurityFocus.com.
Step one is easy: disable the existing cgiemail on your
system. Move it out of your cgi-bin directory or its
equivalent or take away its execute status. Forms using it
will now no longer work.
There is no official, or at least timely, support from MIT
for cgiemail. However various folks
have patched or fixed the exploit individually. One example for
those that have the source code (it’s part of the distribution
available at MIT) is provided here.
Aside from replacing cgiemail with a patched or updated version
the only real alternative is to find or build an alternative. One
of the more popular is called FormMail.
I wanted something that was a little closer to a plug-in
replacement for cgiemail to minimize changes to either the
forms that use it or the templates used. I wrote tmail.pl
which while not quite as full featured as cgiemail, tackles
common cgiemail-like templates with more of an eye to
security.
The major differences that tmail.pl introduces are:
- Template parameters are required by default. Unless
explicitly stated otherwise, it generates an error if a
parameter is used in a template but not present in the form’s
input. - A new type of parameter has been created: “email”. When a
template indicates that a parameter is of type email, some
rudimentary checks are made to ensure that the entered data is in
fact somewhat like a valid email address. - Additional restrictions can be placed on a parameter.
Specifically the value can be scanned for newlines (the source
of the current exploit). If one is found an error results.
In addition, tmail.pl is a Perl script and takes an additional
form parameter which is the name of the template. The template is
typically found relative to the location of the Perl script so
they can be moved to the cgibin directory where they are not
directly readable by site visitors.
tmail.pl can be downloaded
here.
Is there a way to find all pages that use cgiemail? It would be a great service to all of us if someone could find them all and email the webmasters to inform them of the spammer hijacking risk and possible fixes.
“Is there a way to find all pages that use cgiemail?” Not that I’m aware of offhand. Search engine cataloging of the usage of cgiemail is spotty at best, since most of the search engines avoid a lot of dynamic content and/or cgi scripts. Most ISPs are (or should be) on various security mailing lists that have discussed this issue. It’s quite common to find cgiemail on ISP provided web hosts, and if they’re on top of things, they’ll be aware of the problem. Certainly they will be if they get hijacked.
Leo
Well, by default there’s a header field enabled:
“X-Mailer: cgiemail “
If one personally doesn’t expect to recieve mail generated by a web form (which, if one doesn’t have a website with such a form, is a pretty safe bet) one can add a filter to block mails coming with that particular header.
That’s an individual, and not systematic, solution, however. I myself prefer FormMail because the source is more easily modifiable, and you don’t have to compile it.
For the record: tmail.pl is in Perl, and once you download it it’s easy to modify and you can do so to your heart’s content.
Leo
Hello,
It has been brought to my attention that tmail is exploitable. I am in the process of working out with my SA where the problem lies, please feel free to contact me via telephone at 407.445.3033×2167. I am available from 4PM-12AM tuesday through saturday.
A poorly designed template can still be exploited. Do let me know if you find out something more.
Does anyone have a “patched” copy of cgiemail that I can simply ftp upload to my server to overwrite my existing one? I am not a “c” programmer and don’t have a compiler either.
Any help is appreciated.
Don’t know if there is one, but this would be the place to start looking: http://web.mit.edu/wwwdev/cgiemail/
Hello,
I would like to use tmail.pl but my hosting service does not support it. They say to use the NET::SMTP component, as opposed to Sendmail.
Do you know what that means and how I get around it?
Thanks
Maryann
Thanks for this script, Leo. The only problem that I am having is getting the prefix “required-” to work. I must be missing something, but if the form has a field input name “required-firstName” and the template has [required-firstName] one can still send the form without filing in the first name field.
Other than that, it works great and I love the new parameter prefixes. Thanks.
Rick
For a real solution that introduces an optical security feature bundled in a PHP program that is easily implemented and thoroughly documented FOR FREE, go to:
http://www.dagondesign.com/articles/secure-php-form-mailer-script
Regarding question: Is there a way to find all pages that use cgiemail?
Well, the simple way would be to remove all permissions from the cgi-script…then they will come to you when it no longer works!