Tim Starling wrote:
UsernameBlacklist makes the servers crash when people
try to create
accounts. This is due to the excessively complex regexes entered by
administrators. PCRE has lots of bugs which allow you to crash it with
arbitrary regexes, but as long as you keep them simple (like in
SpamBlacklist), it's not a problem.
The extension has been disabled pending a workaround.
This is quite surprising, given that I've added some some almost
ridiculously complicated regexes to MediaWiki:Titleblacklist on enwiki,
and I've heard no reports of problems from that. Looking at the code
quickly, the only major difference between the two extensions seems to
be that the title blacklist checks each regexp separately, while the
username blacklist tries to concatenate them all into one mega-regex.