Re: [Full-disclosure] Samba Remote Zero-Day Exploit



You need admin rights to create junctions. At that point, path
constraints aren't relevant, just psexec and get not only arbitrary
path but arbitrary code.

The fix is to do what everybody with a directory traversal bug has to
do, block out of path relative directories. In this specific case,
prevent the creation of symlinks where the target is out of the SMB
share's range. (Still allow navigation to such symlinks if one exists,
though.)



On Feb 6, 2010, at 8:21 AM, "Stefan Kanthak" <stefan.kanthak@xxxxxxxx>
wrote:

Dan Kaminsky wrote:

[...]

(On a side note, you're not going to see this sort of symlink stuff
on
Windows,

What exactly do you mean?
Traversing symlinks on the server/share, or creation of "wide"
symlinks
by the client on the server/share?

Since Windows 2000 NTFS supports "junctions", which pretty much
resemble
Unix symlinks, but only for directories.
See <http://support.microsoft.com/kb/205524/en-us>

On the server, create a junction in your share and let it point to an
arbitrary local directory outside the share, and clients connected to
that share can enter the junction and access the "linked" directory.

If you have write access to the share from the client you can create
a "wide" junction there too, just as the OP showed with smbclient/
samba.

and Samba is supposed to match Windows semantics in general.

Except a mapping of directory symlinks to junctions for example.-(

Stefan


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