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[Full-disclosure] Vim 7.2c.002 Fixes Arbitrary Command Execution when Handling Tar Archives

From: Jan Minář <rdancer_at_nospam>
Date: Fri Aug 08 2008 - 13:56:16 GMT
To: vim-dev@vim.org, full-disclosure@lists.grok.org.uk, bugtraq@securityfocus.com


Vim 7.2c.002 Fixes Arbitrary Command Execution when Handling Tar Archives

  1. SUMMARY
Product : Vim -- Vi IMproved
Version : Vim >= 7.0 (possibly older), fixed in 7.2c.002

           autoload/tar.vim version >= 9 (possibly older) Impact : Arbitrary code execution Wherefrom: Local, remote Original : http://www.rdancer.org/vulnerablevim-tarplugin.v3.html

Vim update fixes a vulnerability that can lead to potential arbitrary code execution when handling tar archives. The fnameescape() function does not sanitize input properly, which renders code that uses it vulnerable. Patch 7.2c.002 fixes the vulnerability.

2. BACKGROUND   ``Vim is an almost compatible version of the UNIX editor Vi. Many new     features have been added: multi-level undo, syntax highlighting,     command line history, on-line help, spell checking, filename     completion, block operations, etc.''

  • Vim README.txt

 ``When one edits a *.tar file, this plugin will handle displaying a    contents page. Select a file to edit by moving the cursor atop    the desired file, then hit the <return> key. After editing, one may    also write to the file.''

  • Tar File Interface (pi_tar.txt) 3. VULNERABILITY
In statements such as the ones in ``$VIMRUNTIME/autoload/tar.vim'' on lines 163, 308, 368, 407, and 419 (tar.vim version 20 (2008-07-30)): 163 exe "r ".fnameescape(a:tarfile) 308 exe "cd ".fnameescape(tmpdir) 368 exe "w! ".fnameescape(fname) 407 exe "e! ".fnameescape(tarfile) 419 exe "cd ".fnameescape(curdir)

fnameescape() makes the untrusted file name safe as an argument to ``execute''. However, the commands called by ``execute'' will in turn each interpret the untrusted file name again. This can be still used for arbitrary command execution. Another level of sanitizing/escaping is needed in order to make the statements safe.

4. EXPLOIT No exploit code is provided.

5. FIX Fixed by patch 7.2c.002[2]: fnameescape() was updated to escape a leading '+' and '>', and a single '-'.

6. REFERENCES
[1] Collection of Vulnerabilities in Fully Patched Vim 7.1

    http://www.rdancer.org/vulnerablevim.html
[2] Patch 7.2c.002

    http://groups.google.com/group/vim_dev/msg/80882b9ee9293139     http://ftp.vim.org/pub/vim/unstable/patches/7.2c/7.2c.002

7. COPYRIGHT This advisory is Copyright 2008 Jan Minar <rdancer@rdancer.org>

Copying welcome, under the Creative Commons ``Attribution-Share Alike'' License http://creativecommons.org/licenses/by-sa/2.0/uk/

Code included herein, and accompanying this advisory, may be copied according to the GNU General Public License version 2, or the Vim license. See the subdirectory ``licenses''.

Various portions of the accompanying code were written by various parties. Those parties may hold copyright, and those portions may be copied according to their respective licenses.

8. HISTORY 2008-08-08 Sent to: <vim-dev@vim.org>, <full-disclosure@lists.grok.org.uk>, <bugtraq@securityfocus.com>
2008-08-08 Patch 7.2c.002 released, fixing the vulnerability 2008-08-06 Reported to Vim maintainer



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