[pmwiki-users] Error encountered with upgrade to 2.2 beta 65

Henrik henrik.bechmann at sympatico.ca
Sat Mar 29 14:12:12 CDT 2008

Here's a good one, following up on webserve.ca's use of mod_security.

I finally convinced them to allow "http://" in postings, which again 
allows links to external websites, but there was still an apparently 
random problem ("Forbidden" error) occurring in long wiki page postings. 
After a couple of hours of diagnosis, it turns out that the words 
"select" and "from" cannot follow each other anywhere in a posting, 
regardless of location in the posting, and regardless of either one 
being embedded in longer words.

So the phrase "select from" will trigger the Forbidden error. But also:

if a user posts the sentence: "I select an apple from a pile", the error 
will occur.

if a user posts: "I selected a piece of fromage (French for cheese)", 
the error will occur, because the word "from" is embedded in the word 
"fromage", and follows the word "select" even though "select" is 
embedded in the word "selected".

And if the word "select" occurs at the top of the document, and the word 
"from" occurs several paragraphs later, the "Forbidden" error will occur.

I have submitted this diagnosis to them.

So Patrick: casting your mind back to your days as a professor (and 
bearing in mind that you are one of the world's leading authorities on 
regular expressions), if you had given a student the assignment to add a 
filter to mod_security against a "select from" problem, and they came up 
with the above results, what mark would you give them? What would you 
say to them?<grin>

I have since signed up with canadianwebhosting.com, and have begun the 
process of moving my websites away from webserve.ca. The above proves 
(if any more proof were needed) that they are basically dangerous.

- Henrik

Patrick R. Michaud wrote:
> On Wed, Mar 26, 2008 at 04:02:06PM -0400, Henrik wrote:
>>    Thanks for pointing me to the specific module responsible for the
>>    security, Patrick, and for the reality check.
>>    I am continuing to investigate alternate webserver hosts.
>>    canadianwebhosting.com looks promising. They use an suPHP scheme which
>>    looks tight but workable, with "Your scripts and directories can have a
>>    maximum of 755 permissions" (all files have the same owner with rwx). I
>>    presume that would be workable? Would I have to reconfigure the
>>    umask(002); statement in pmwiki.php for this?
> You might want to add umask(022); near the beginning of your config.php,
> but other than that you should find that things run much better under
> suPHP.
> Pm
>>  On Sun, Mar 23, 2008 at 10:11:49AM -0400, Henrik wrote:
>>  This security change by my webhost is confirmed. In response to my query
>>  they sent me the following response.
>>  =============================
>>  The web server security is setup such that it will automatically block system related words while posting data from php based applications, as this may lead to web server exploit. We request you to stop using system related words in your applications.
>>  =============================
>>  So suddenly none of my websites can post external links (with the string
>>  "http://" anywhere in the page), and hundreds if not thousands of pages
>>  that have this protocol embedded are suddenly uneditable.
>>  Truly horrible. A complete nightmare!
>>  But nothing to do with PmWiki.
>>  Just to follow up on this -- this particular issue is described
>>  at http://www.pmwiki.org/wiki/PmWiki/Troubleshooting#mod_security .
>>  There is no PmWiki-based workaround to it, as the problem is well
>>  outside of PmWiki (as you've recognized).
>>  I've never heard of someone using mod_security to block "http://"
>>  before, though, so that's new (and an additional reason to doubt
>>  the sanity of the webhosting provider).  Note that this security
>>  measure affects not only PmWiki, but also any application that
>>  tries to use an input form where someone might want to provide
>>  an http:// link (e.g., comments to blog postings, shopping carts,
>>  etc.).
>>  Pm
>>  --
>>  Henrik Bechmann
>>  www.bechmann.ca
>>  Webmaster, www.dufferinpark.ca


Henrik Bechmann
Webmaster, www.dufferinpark.ca

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