||PHP 4.2.0 and 4.2.1 have an error in the handling of POST requests which
can lead to the corruption of memory, and the usual bad consequences. According to this alert, the vulnerability can only be used for denial of service on x86 systems - there is no way to get it to run exploit code. SPARC/Solaris systems are apparently vulnerable to full remote compromise.
According to the CERT Advisory,
almost every Linux distributor, it seems, ships older (and thus not vulnerable) versions of PHP.
Note that, sometimes, systems thought to be safe from remote compromise turn out to be vulnerable to a modified attack, so x86 users should not relax too much. The solution, for those systems with PHP
4.2.0 or 4.2.1 installed,
is to upgrade to PHP 4.2.2.
For more information see the alert from
the discover of the vulnerability, Stefan Esser of e-matters GmbH,
or the security
advisory from the php team.
CERT Advisory: CA-2002-21 Vulnerability in PHP