From the description of the code, it seems that 1) the code doesn't use taint - the substitution on the cookie failed, so the cookie would still have been tainted. 2) the cookie is interpolated into a string, then evalled. I'm pretty sure that leaves many other possibilities to execute arbitrary code.

In this specific case, there is a test that a filename including the cookie string exists before the eval. Poisoned null on the stat call allows that test to be fooled. Without the poisoned null trick, only existing directory names can be shoved into the string to be evaled, making the exploit harder and maybe impossible in some cases.

I bet there are more scripts out there that are currently exploitable due to poisoned null. Wouldn't it be nice (from the web hoster's point of view) for those vulnerabilities to vanish the next time the hoster upgrades Perl ?

In reply to Re^4: Why do poisoned null attacks still work ? by pubnoop
in thread Why do poisoned null attacks still work ? by pubnoop

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