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Re: Microsoft Windows Vista/2003/XP/2000 file management security issues
From: "M. Burnett" <mb () xato net>
Date: Fri, 9 Mar 2007 10:43:50 -0700

But we'll have to agree to disagree. Your security scenarios are just
bizarre. It's a lot easier to hack people then going through all the
interations you suggest.

Roger, don't be so hard on 3APA3A for this. You can't judge a vulnerability
based on current scenarios because we really can't begin to imagine how
these things might be exploited in future attacks. For example, the attack
of deleting someone's folder and re-creating it before they set permissions
sounds bizarre until someone makes a tool that does that automatically to
all new folders. It changes everything when even the front desk secretary
can pull off the attack. 

And even if it would be lame for someone to set up a folder where this would
be possible, people will still set up folders where this is possible. It's
important for us to be aware of the risks of these configurations. And you
have to admit, it is pretty amazing he found something we all missed for the
last ten years, despite how simple it is. 
 
Finally, I don't think 3APA3A is over hyping this issue beyond what it
really is. He acknowledges that it isn't really a vulnerability and he's not
submitting press releases to all the mainstream media. He gave Microsoft
fair notice and awaited their decision and he's not screaming that everyone
must abandon Windows. But he is informing the security community of
something that we certainly should be aware of. 


Mark Burnett
http://xato.net

 
For one, I've been a sys admin for 20 years and NEVER created a private
folder under a public folder. Not in my Novell days, not in my Windows
days. The only time I've seen a private folder created under a public
folder is the \Users folder, and in that case, the users only have Read
and List access to the parent \Users folder, and then Full Control to
their own folders.

I mean let's debate why users get Full Control to their own folders in
the first place. That's a common scenario (it's on nearly every
network) and its almost always too many permissions. Do I want my
regular end-users changing their folder's security permissions? No.
Should any regular end-user have Full Control to any share? No, for the
same reason.  These are valid, common, security points that really do
beg further discussion.

You're just making up crap up that isn't overly realistic in the world,
then going further to assume that a bonehead administrator compounds
the problem by making further insecure decisions.

You are essentially say, "If you misconfigure your system and make
further insecure choices, someone can hack you." Duh.

There's a reason why your "announcements" aren't making the news
media...because it isn't news.

With that said, you have something valid to say, but so far it just
isn't a "security vulnerability" that people need to be aware of.

You're a smart person, concentrate on issues that will really give us
bang for the buck discussions and issues.

Roger

*****************************************************************
*Roger A. Grimes, InfoWorld, Security Columnist
*CPA, CISSP, MCSE: Security (2000/2003/MVP), CEH, yada...yada...
*email: roger_grimes () infoworld com or roger () banneretcs com
*Author of Professional Windows Desktop and Server Hardening (Wrox)
*http://www.amazon.com/gp/product/0764599909
*****************************************************************
http://winblogs.security-feed.com
Server Hardening, NTFS
-----Original Message-----
From: 3APA3A [mailto:3APA3A () SECURITY NNOV RU]
Sent: Friday, March 09, 2007 7:09 AM
To: Roger A. Grimes
Cc: bugtraq () securityfocus com; full-disclosure () lists grok org uk
Subject: Re[2]: Microsoft Windows Vista/2003/XP/2000 file management
security issues

Dear Roger A. Grimes,

--Friday, March 9, 2007, 7:31:54 AM, you wrote to
3APA3A () SECURITY NNOV RU:

RAG> If Alice deletes Bob's folder (which she could do in some
scenarios
RAG> because she has the write/modify permission) and re-creates it,
she
RAG> becomes  the Creator Owner and now Bob no longer has the ability
to
RAG> set permissions on it.

As a folder owner Alice can give any permissions to Bob she wants.

RAG> If I take your strange assumptions, Bob could re-discover the
newly
RAG> created folder that Alice made, just like she did (I mean if you
RAG> make up crap scenarios, why can't I), and do the same trick back
to her.

He can, if he knows he must.

RAG> And Windows does have a umask-like function. It's called Creator
Owner.
RAG> It's a well known SID, and the default permissions for it can be
RAG> set so that any granular permission you want can be set to be
default.

I  see  nothing  similar  between Creator Owner and umask. BTW, the
same article  explains  why  Creator  Owner  is not 100% solution and
why you should not rely on Creator Owner in case of DFS replication.

RAG> Vista does have symbolic links, and Windows has supported Junction
RAG> Points (similar to symbolic links) since Windows 2000. The main
RAG> difference is that Junction Points could only point to local
RAG> resources and symbolic links can do remote resources as well.

Junction  points are very close to Unix mounts, I see no any likeness
to symbolic  links.  Junctions  points  (and  by default, symbolic
links in
Vista)  can  only  be  created  by  administrators,  it prevents
symlink attack. And it's right choice.

RAG> You've come up with some strange scenarios below, and in all cases
RAG> I could easily defeat the problem you are suggesting by using
RAG> basic, recommended, security settings.


"You never know what is enough unless you know more than enough."
                                                    William Blake

It's  quite  hard  to defeat the threat without knowing it. I'm
disagree with  you about "recommended security settings". I never saw
"disconnect all  users and close access to the share" or "check you are
still folder owner before copy the data" in instructions on how to
create file/folder with restricted access inside public one. Or "xcopy
/O doesn't guarantee file  can  not  be  accessed  during  copy
operation" or "Do not rely on Creator Owner in case of replication".

RAG> Why  do  you spend your time coming up with such weird scenarios
to
RAG> focus  on?

Roger,  have  you  ever  used  robocopy  or  xcopy  /O? I'm not
security columnist,  I  am  system  administrator/engineer.  For  last
10 years I
develop   and   implement  a  lot  of  corporate  directory
structures,
replications,  and  backup/restore  policies  for  many  very
different organizations.  I explain mistakes I can personally make and
sometimes I personally  did (mixing secure and insecure data,
implementing automatic replication  to  unprotected folders,
implementing data restore policies where  user  can  ask  system
administrator  to  restore some directory structure  to  user
accessible folder, etc). May be I'm only dumb person who  does
mistakes  like  that,  most probably not. I call it "properly placed
rakes to step on".

RAG> You're  obviously  a  creative  guy  with  some Windows security
RAG> smarts.

Thanks.

RAG> Why  not  focus on more realistic scenarios with more  real-world
RAG> use? There's plenty of them for us to focus on and to try and
RAG> solve.

Roger,  of  cause  next  time  I  should  concentrate on a single-
packet exploitable overflow in IPv6 stack to interest InfoWorld
readers. I will not,  because  it's  nothing interesting for me in
searching yet another buffer  overflow.  Let  another  creative  guys
who are professional in vulnerability  researching  to  dig it. They
have tools, time and money.
For me, most valuable vulnerability is one simple enough to be
exploited with notepad, because it can be noted by everyone, but was
unnoticed for 10 years.

RAG> Roger

RAG> *****************************************************************
RAG> *Roger A. Grimes, InfoWorld, Security Columnist *CPA, CISSP, MCSE:
RAG> Security (2000/2003/MVP), CEH, yada...yada...

3APA3A. MCSE/MCT since Windows NT 4.0.

RAG> *email: roger_grimes () infoworld com or roger () banneretcs com *Author
RAG> of Professional Windows Desktop and Server Hardening (Wrox)
RAG> *http://www.amazon.com/gp/product/0764599909
RAG> *****************************************************************


RAG> -----Original Message-----
RAG> From: 3APA3A [mailto:3APA3A () SECURITY NNOV RU]
RAG> Sent: Thursday, March 08, 2007 2:59 PM
RAG> To: bugtraq () securityfocus com; full-disclosure () lists grok org uk
RAG> Subject: Microsoft Windows Vista/2003/XP/2000 file management
RAG> security issues


RAG> This   is   an   article   I   promised   to   publish   after
Windows
RAG> ReadDirectoryChangesW  (CVE-2007-0843)  [1] issue. It should
RAG> explain why you must never place secure data inside insecure
directory.



RAG> Title: Microsoft Windows Vista/2003/XP/2000 file management
RAG> security issues
RAG> Author: 3APA3A, http://securityvulns.com/
RAG> Vendor: Microsoft (and potentially another vendors)
RAG> Products:  Microsoft  Windows Vista/2003/XP/2000, Microsoft
resource kit
RAG>            for Windows 2000 and different utilities.
RAG> Access Vector: Local
RAG> Type: multiple/complex (weak design, insecure file operations,
etc)
RAG> Original advisory:
http://securityvulns.com/advisories/winfiles.asp
RAG> Securityvulns.com news:
RAG> http://security.nnov.ru/news/Microsoft/Windows/files.html

RAG> 0. Intro

RAG> This  article contains a set of attack scenarios to demonstrate
RAG> security weakness in few very common Windows management practices.
RAG> Neither of the problem  explained  is critical, yet combined
together they should force
RAG> you   to   review   your   security   practices.   I   can't  even
say
RAG> "vulnerabilities"   because   there   is   no  something  you can
call
RAG> "vulnerability". It's just something you believe is secure and
it's not.

RAG> 1.1 Problem: inability to create secured file / folder in public
one.
RAG>     Attack: folder hijack attack

RAG> First,  it's simply impossible with standard Windows interface to
RAG> create something secured in insecure folder.

RAG>  Scenario  1.1:

RAG>  Bob  wishes  to  create "Bob private data" folder in "Public"
RAG> folder to place  few private files. "Public" has at least "Write"
RAG> permissions for "User" group. Bob:

RAG>      I   Creates "Bob private data" folder
RAG>      II  Sets permission for folder to only allow access to folder
RAG> himself
RAG>      III Copies private files into folder

RAG>   Alice wants to get access to folder Bob created. She

RAG>      Ia  Immediately  after  folder  is  created,  deletes "Bob
private
RAG>          data"  folder  and creates "Bob private data" folder
again (or
RAG>          simply  takes  ownership  under  "Bob  private data"
folder if
RAG>          permissions allow). It makes Alice folder owner.
RAG>      IIa Immediately  after  Bob  sets permissions, she grants
herself
RAG>          full control under folder. She can do it as a folder
owner.
RAG>      IIIa  Reads  Bob's  private  files,  because  files
permissions are
RAG>          inherited from folder

RAG>   Alice   can  use  "Spydir"
RAG> (http://securityvulns.com/soft/)  tool  to
RAG>   monitor  files  access  and automate this process. As you can
see, [1]
RAG>   elevates this problem significantly.

RAG>   This   is  not  new  attack.  Unix  has  "umask"  command  to
protect
RAG>   administrators and users. Currently, Windows has nothing
similar.

RAG>   CreateFile() API supports setting file ACL on file creation
(just like
RAG>   open()  allows  to set mode on POSIX systems). ACL can be
securely set
RAG>   only  on  newly  created  files.  This raises a problem of
secure file
RAG>   creation.

RAG> 1.2  Problem: Inability to lock / securely change permissions of
already
RAG>      created file
RAG>      Attack: pre-open file/directory attack.

RAG>   There  are  few  classes  of insecure file creation attack
(attempt to
RAG>   open   existing  file),  exploitable  under  Unix  with
hardlinks  or
RAG>   symlinks.  It's  believed  Windows  is  not vulnerable to this
attacks
RAG>   because

RAG>     I.  There  is  no  symlinks  under Windows. Symlink attacks
are not
RAG>         possible.
RAG>     II. Security  information  in  NTFS  is  not  stored  as  a
part of
RAG>         directory entry, it's a part of file data. Hard link
attacks are
RAG>         not possible.
RAG>     III. File  locks  in  Windows  are  mandatory.  It  means,  if
one
RAG>          application  locks  the file, another application can not
open
RAG>          this  file, if user doesn't have backup privileges. It
mitigate
RAG>          different file-based attacks.

RAG>   There  is at least one scenario, attacker can succeed without
symbolic
RAG>   link:  to  steal  data  written to file created without check
for file
RAG>   existence regardless of file locks and permissions.

RAG>   Attack description: if attacker can predict filename to be
written, he
RAG>   can  create file, open it and share this file for all types of
access.
RAG>   Because  locking  and  permissions  are  only  checked  on  file
open,
RAG>   attacker  retain  access  to  the  file  even  if it's locked
and it's
RAG>   permissions are changed to deny file access to attacker.

RAG>   Exploit (or useful tool):
RAG> http://securityvulns.com/files/spyfile.c

RAG>   Opens  file, shares it for different types of access and logs
changes,
RAG>   keeping the file open.

RAG>   Compiled version is available from
http://securityvulns.com/soft/

RAG>   Scenario 1.2.1:

RAG>    Bob is now aware about folder hijack attack. He use xcopy /O /U
/S to
RAG>    synchronize  his  files  to  newly  created  folder.  xcopy /O
copies
RAG>    security  information (ownership and permissions) before
writing data
RAG>    to file.

RAG>    Alice  use  "Spydir"  to  monitor  newly created folders and
files in
RAG>    Bob's  directory.  She  use Spyfile to create spoofed files in
target
RAG>    directory  and  waits for Bob to run xcopy. Now, she has full
control
RAG>    under  content of Bob's files despite the fact she has no
permissions
RAG>    to access these files.

RAG>    In  a  same  way  directory  content  may be monitored by pre-
opening
RAG>    directory.

RAG>   Scenario 1.2.2:

RAG>    Enterprise  directory  structure  is  replicated every day to
another
RAG>    user-writable  location  in  order  to alow users to recover
suddenly
RAG>    deleted  or  modified files. xcopy or robocopy (from resource
kit) is
RAG>    used  for  replication.  Attacker can hijack content of newly
created
RAG>    files in newly created folders.

RAG>   Same problem may happen on archive extraction or backup
restoration.

RAG>   Vulnerable  applications:
RAG>     xcopy (from all Windows versions),
RAG>     robocopy (Windows  2000  Resource Kit),
RAG>     different archivers
RAG>     backup restoration utilities

RAG>   By  default,  xcopy warns user the file exists, unless /Y or /U
key is
RAG>   specified.  But
RAG>     I.  /Y  is  always  specified  for replication
RAG>     II. /Y  can  be specified via COPYCMD environment variable.
COPYCMD
RAG>     environment    variable   can  be  created  in  autoexec.bat
file.
RAG>     Different situations are possible, where autoexec.bat is
writable by
RAG>     attacker, if:
RAG>      - Default Windows 2000 permissions are used or applied with
domain
RAG>      policy [2].
RAG>      - One can try to re-create autoexec.bat using POSIX subsystem
RAG>     III.  Neither  xcopy  nor  other  utilities  warn user on
existing
RAG>     directory. Pre-open directory attack will always succeed.

RAG>   As you can see, [1] again dramatically elevates this problem.

RAG> 1.3 Problem: user can completely block access to the files
RAG>     Attack: open file deletion
RAG>     (including Windows file replication service DoS)

RAG>     If files is deleted while it's open, it still present in file
system
RAG>     under  it's  old  name  until  close.  Any  operation  on this
file
RAG>     (including  attributes  requests)  fails,  regardless of
application
RAG>     rights and permissions (including backup ones).

RAG>     Exploit:  use  spyfile,  delete  file while it's spied. Now,
without
RAG>     closing  spyfile,  attempt  any  operation on this file (e.g.
try to
RAG>     find it's ownership).

RAG>     Scenario 1.3.1

RAG>     Now Bob found an copy application to securely copy files. It
deletes
RAG>     old file before creating new one. But it fails if Alice tries
to spy
RAG>     on  Bob  files,  because  attempt  to delete file succeeds,
but file
RAG>     still present and is unmanageable.

RAG>     Scenario 1.3.2

RAG>     Windows  file  replication  service  (FRS) is used to
replicate data
RAG>     between  2  public  DFS  folders  to  distribute  load.
Folder  has
RAG>     permissions:
RAG>      Everyone: Add & read
RAG>      Creator Owner: Full Control
RAG>     Thouse, Alice has no permissions to delete files created by
Bob.

RAG>     Replicated  folder  is  available as a share on 2 different
servers:
RAG>     \\SERVER1\Share    and    \\SERVER2\Share.    Bob    is
connected
RAG>     to \\SERVER1\Share.

RAG>     Alice uses "Spydir" to monitor files creation by Bob. Every
time Bob
RAG>     creates  new  file  on  \\SERVER1\Share, Alice use spyfile to
create
RAG>     file  with same name on \\SERVER2\Share. It effectively leads
to FRS
RAG>     collision.  While  trying  to resolve collision, FRS fails to
delete
RAG>     file  created  by  Alice  and  Bob file is deleted (original
file is
RAG>     moved to special hidden folder only accessible by
administrator).

RAG>     Workaround:  never  try  to  use  creator-owner based
permissions in
RAG>     replicated folders.

RAG>     Again, [1] seriously escalates this problem.

RAG> 2. Conclusion:

RAG>   It's  simply impossible to securely create something in public
folder.
RAG>   At least DoS conditions are always possible.
RAG>   Developers should  not  consider mandatory file locking as a
security
RAG>   feature.
RAG>   Developers  should  care about secure file creation to store
sensitive
RAG>   information.  CREATE_NEW  should  always be used and ACL should
be set
RAG>   with  lpSecurityAttributes  of CreateFile. No attempt to open
existing
RAG>   file should be made.
RAG>   Never  try  to  create secure folder in public one. If you are
forced,
RAG>   disconnect     all   users   before   this   operation.
RAG>   Never  use  replication,  archive  extraction  or  backup
restore  to
RAG>   user-accessible folder.
RAG>   Bob and Alice should finally marry.

RAG> 3. Vendor:

RAG>   All timelines are same with [1].

http://passwords.security-feed.com
RAG> [1]. Microsoft Windows ReadDirectoryChangesW information leak
RAG> (CVE-2007-0843)
RAG> http://security.nnov.ru/news/Microsoft/Windows/ReadDirector.html
RAG> [2]. Windows 2000 system partition weak default permissions
RAG> http://securityvulns.ru/news2205.html
http://xato.net
RAG> --
RAG> http://securityvulns.com/
RAG>          /\_/\
RAG>         { , . }     |\
RAG> +--oQQo->{ ^ }<-----+ \
RAG> |  ZARAZA  U  3APA3A   } You know my name - look up my number (The
RAG> Beatles)
RAG> +-------------o66o--+ /
RAG>                     |/



--
~/ZARAZA http://securityvulns.com/
Но ведь кому угодно могут прийти в голову яйца, пятки и епископы. (Лем)

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