Re: DoS in debian (potato) proftpd: 1.2.0pre10-2.0potato1
At 03:40 PM 3/29/2002, martin f krafft wrote:
ls */../*/../*/../*/../*/../*/../*/../*/../*/../*/../*/../*/../*
...
DenyFilter \*.*/
Just as a quick question, why not deny the string "/../" (you may have to
deny the regex "/\.\./", depending how the filter in question works)?
As far as I can tell, it's the ability to embed "/../" into a path that is
at the root of this, far more than the ability to embed wildcards. I can't
think of a situation in which "/../" should appear in a user-supplied path,
except after a string of repeated "../"s.
The workaround suggested by Mr Krafft would disable some useful
functionality - one large user of mine, for instance, was keen to have my
own software evaluate wildcards in the body of the path, which Mr Krafft's
workaround disables completely. They even paid for the privilege (not
enough, but they paid ;-))
So, let's see, a regex that would deny "/../", except as part of a string
of such...
One bash would be "[^/.].*/\.\./" - matching "/../" if it's after any
character other than '/' or '.'. Doubtless someone can come up with
something better.
Alun.
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