This is exploitable in an obvious way; “../” can be included in the filename, and it can be used to open any file ending in “.html” that’s readable by the web user. However, there’s a second, less obvious exploit path.
If magic\_quotes\_gpc is off, the following is possible:
test.php?filename=../../../../../../etc/passwd%00
PHP stores strings internally as binary-safe, but the include() requires a syscall, which expects a nil-terminated string. The result is that the syscall considers the string over at the \0, and opens /etc/passwd. PHP should really check to see if the binary-safe string contains nils before the syscall, and fail with an error if it does.
---
In __PERL__:
open IN,”foo\0bar”;
causes the syscall:
open(”foo”, O_RDONLY|O_LARGEFILE)
---
In __Ruby__:
File.open(”foo\0bar”,’r');
causes the syscall:
open(”foo”, O_RDONLY|O_LARGEFILE)
---
__Python__ appears to be safe:
open(”foo\0bar”,”r”);
throws an error:
TypeError: file() argument 1 must be (encoded string without NULL bytes), not str
