SECURITY.NNOV: directory traversal and path globing in multiple archivers

[3APA3A <3APA3A () SECURITY NNOV RU>]

Hello,

Topic:                    Directory traversal and path globing in
                          multiple archivers
Author:                   3APA3A <3APA3A () security nnov ru>
Affected Software:        GNU tar <= 1.13.19, Info-Zip UnZip <= 5.42,
                          RARSoft rar <= 2.02, PKWare pkzipc <= 4.00
Not affected:             rar 2.80, WinZIP 8.0
Risk:                     average
Released:                 July, 2, 2001
SECURITY.NNOV advisories: http://www.security.nnov.ru/advisories


Background:

Archive  extraction  is  usually treated by users as a safe operation.
There are few problems with files extraction though.

Problem(s):

Among  them:  huge  files with high compression ratio are able to fill
memory/disk  (see  "Antivirus scanner DoS with zip archives" thread on
Vuln-Dev),  special device names and special characters in file names,
directory  traversal  (dot-dot  bug). Probably, directory traversal is
most  dangerous  among  this  bugs, because it allows to craft archive
which  will  trojan  system  on  extraction. This problem is known for
software  developers,  and  newer  archivers usually have some kind of
protection.  But  in  some  cases  this  protection is weak and can be
bypassed.  I did very quick (approx. 30 minutes, so may be I've missed
something) researches on few popular archivers. Results are below.


Detailed info:

GNU tar (all platforms):

 tar  below  1.13.19  including  latest  releases  has  no any ".." or
 absolute  path  protection.  Tar development team was contacted. They
 replied  they're  aware  of  problem  and current development version
 1.13.19  implements  some  kind of protection but it doesn't work for
 most  cases  due  to  bug in coding. Exploitation scenario was passed
 back  to  development  team. I hope it will work then 1.13.19 will be
 finally  released.  See  attached  patch (tar-1.13.19.patch). 1.13.19
 sources can be obtained from ftp://alpha.gnu.org/gnu/tar/

Info-Zip's UnZip (all platforms):

 all  versions  have neither .. nor absolute path protection. No reply
 from vendor. See attached patch (unzip-5.42.patch).

PKWare's PKZip (Windows):

 console  version was tested. It's vulnerable, if archive is extracted
 with  -rec (recursive) option. If this option is not given archive is
 extracted without directory structure. All versions up to latest 4.00
 are  vulnerable.  Program  is shareware, no sources available. Vendor
 contacted but status of patch unknown.

RARsoft (Eugene Roshal's) RAR (all platforms):

 Directory  traversal  protection  was  implemented  in rar 2.02. This
 protection  can  be bypassed. Eugene Roshal was contacted and replied
 latest  version of rar (2.80) is absolutely safe. It's true, but 2.02
 is latest available version in most Unix ports (2.80 is available for
 Windows  and Linux, you can use Linux version if your system supports
 Linux emulation). Program is shareware, no sources available.

WinZip (Windows):

 Behavior  is  close  to  ideal. Console version doesn't extract files
 with  ".."  until  special  switch  is not selected, windowed version
 warns user on ".." about possible impacts of such extraction.

Exploitation:

 Exploitation  of  path globing and directory traversal under Windows
 exploitation  is  trivial.  On  most unix system to exploit directory
 traversal  you should guess level of directory file will be extracted
 to.  tar  and  rar are able to create files with permission different
 from  umask,  it  makes  it  possible to create executables. Only tar
 overwrites target files without prompt by default.

 Demo archives can be found on
 http://www.security.nnov.ru/advisories/archdt.asp

Workaround:

 List  content  of  archive  before extraction if archive was obtained
 from  untrusted source (but have in mind that name of the file can be
 with  something  like  ../^H^H^H  -  do not trust your eyes, use some
 program).  Never automate archive extraction, or use jail if you need
 automation.  Be  sure  never  run  extraction from user with elevated
 privileges.

Solution:

 Wait  for  vendor  patch  or  use checked archivers or apply attached
 patches on your own risk.


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Attachment: tar-1.13.19.patch
Description:

Attachment: unzip-5.42.patch
Description: