XF 1.5 Specific phrases causing server error (possible bug)

[Live Free]

I haven't posted this a a bug because I haven't recreated it on a clean installation, and there's a good chance it's server configuration. I was hoping someone could shed some light on it. Two members have encountered this issue posting two different threads.

Basically, a two members tried posting and got an internal server error. They were unable to make the post, and I believe it's due to the specific phrase/sequence of characters in their post. I've encounted this before and it was due to Xenforo or the server trying to prevent SQL commands.

The first message:

As for 1^o. X^1/x^1 = 1 simplifies to x^(1-1) = 1

Posting the above in any thread gets a 500 server error and "Fetch failed; returning offline page instead. TypeError: Failed to fetch."

The same or similar problem was encountered when posting different content in a different thread. By reducing the full size of the message we have narrowed the problematic text down to something in this block:

...
As a selected Candidate Trustee, take a look at the not so distant past, and then a look at the story of our recent catastrophic global events. Decide what role you want to have in the Third Age of Man...
...

“Gohd! This is going to be so much not fun!” Baker said as his screen went local, “was this my idea? What a moron! How much of this concurrent live crap do I have to do? Yeah, yeah, I know, dammit! As much as possible!”

He turned away from the screen as the ultra classified story, of the formerly silent guardian of humanity, was revealed to the candidates… with some plastic attempt at style.

The above was eventually successfully posted by the member after several attempts of posting, eventually being sucessful by posting a partial post (part of it's not listed) and then using the edit function to add the rest.

Other information:

- The content in this thread causes an error if you press "Use BBCode Editor", but *not* if you press "Reply".
- If attempted a few times it will block you from the site for a few hours (timeout error)

My major concern is unseen problems and the possibility other members are experiencing this and not reporting it.

 

[TPerry]

Is your site using mod_security? If so, have you checked to log to see if that is getting blocked.
It's a security rule of some type most likely, especially with your commenting on the fact that it blocks you out for a few hours if attempted a few times.

 

[MJ0730]

...
As a selected Candidate Trustee, take a look at the not so distant past, and then a look at the story of our recent catastrophic global events. Decide what role you want to have in the Third Age of Man...
...

“Gohd! This is going to be so much not fun!” Baker said as his screen went local, “was this my idea? What a moron! How much of this concurrent live crap do I have to do? Yeah, yeah, I know, dammit! As much as possible!”

He turned away from the screen as the ultra classified story, of the formerly silent guardian of humanity, was revealed to the candidates… with some plastic attempt at style.

Old, but adding some info for anyone else who runs across this. The bolded words are what's causing the failure. Don't have the root cause yet, but will try to update if I find out more.

 

[beerForo]

Is your site using mod_security? If so, have you checked to log to see if that is getting blocked.

 

[MJ0730]

Didn't know what that was, but yeah. That module had some default regex rule blocking lots of SQL terms

 

[beerForo]

Have your host whitelist the rules causing the issues.

 

[MJ0730]

Have your host whitelist the rules causing the issues.

Yeah, I did. Thanks.