03-May-2012
There is a vulnerability in certain CGI-based setups (Apache+mod_php and nginx+php-fpm are not affected)
that has gone unnoticed for at least 8 years. Section
7 of the CGI spec states:
Some systems support a method for supplying a [sic] array of strings to the
CGI script. This is only used in the case of an `indexed' query. This
is identified by a "GET" or "HEAD" HTTP request with a URL search
string not containing any unencoded "=" characters.
So, requests that do not have a "=" in the query string are treated
differently from those who do in some CGI implementations. For PHP this
means that a request containing ?-s may dump the PHP source code for the
page, but a request that has ?-s&=1 is fine.
A large number of sites run PHP as either an Apache module through
mod_php or using php-fpm under nginx. Neither of these setups are
vulnerable to this. Straight shebang-style CGI also does not appear to
be vulnerable.
If you are using Apache mod_cgi to run PHP you may be vulnerable. To see
if you are, just add ?-s to the end of any of your URLs. If you see your
source code, you are vulnerable. If your site renders normally, you are not.
To fix this, update to PHP 5.3.12 or PHP 5.4.2.
We recognize that since CGI is a rather outdated way to run PHP, it may not be feasible to
upgrade these sites to a modern version of PHP. An alternative is to
configure your web server to not let these types of requests with query
strings starting with a "-" and not containing a "=" through. Adding a
rule like this should not break any sites. For Apache using mod_rewrite
it would look like this:
RewriteCond %{QUERY_STRING} ^(%2d|-)[^=]+$ [NC]
RewriteRule ^(.*) $1? [L]
If you are writing your own rule, be sure to take the urlencoded ?%2ds
version into account.
Making a bad week worse, we had a bug in our bug system that toggled the
private flag of a bug report to public on a comment to the bug report
causing this issue to go public before we had time to test solutions to
the level we would like. Please report any issues via bugs.php.net.
For source downloads of PHP 5.3.12 and PHP 5.4.2 please visit
our downloads page, Windows binaries can be found
on windows.php.net/download/. A
ChangeLog exists.