[VSA0402 - openftpd - void.at security notice]

Overview
========

We have discovered a format string vulnerability in openftpd
(http://www.openftpd.org:9673/openftpd). OpenFTPD is a free,
open source FTP server implementation for the UNIX platform.
FTP4ALL is not vulnerable (it doesnt use that message system).

Affected Versions
=================

This affects openftpd version up to 0.30.2. This includes
also the old version 0.29.4.

Impact
======

Middle.
Remote Shell Access when you have an working FTP user account.

Workaround:
===========

Apply the following patch or upgrade to the latest CVS version.

cat > openftpd_formatstring.patch << _EOF_
- --- openftpd-daily.orig/src/misc/msg.c 2004-07-05 22:02:43.000000000 +0200
+++ openftpd-daily/src/misc/msg.c 2004-07-13 18:05:01.000000000 +0200
@@ -319,7 +319,7 @@
while (fgets(buff, 67, file)) {
if (*(buff+strlen(buff)-1) == '\n') *(buff+strlen(buff)-1) = 0;
sprintf(str, " !C| !0%-66s !C|!0\n", buff);
- - printf(str);
+ printf("%s", str);
}
fclose(file);
printf("!C \\__________________________________________________!Hend of message!C__/!0\n");
_EOF_

Details
=======

When a user sends a message to another user an external program will be
called (msg). It is used for the OpenFTPD message handling.

andi@hoagie:~$ ncftp
...
...
ncftp / > site msg purge
All the messages in trash box purged.
ncftp / > site msg send andi "AAAA%08x|%08x|%08x|%08x|%08x|%08x|%08x|%08x|%08x|%08x]"
Message sent to andi.
ncftp / > site msg read

._______________________________________________________________________
_.
| Message sent from: andi Tue 13/07/2004 18:28:46 |
| |
| AAAA0804c1e5|5e8457e0|2b379fc0|00000000|5e84572c|5e84568c|fbad8001|43212
020|3021207c|41414141] |
\__________________________________________________end of message__/
Messages moved to archive box.
...
...

Lets have a look at the source code:

[openftpd-daily/src/misc/msg.c, function cat_message()]
...
while (fgets(buff, 67, file)) {
if (*(buff+strlen(buff)-1) == '\n') *(buff+strlen(buff)-1) = 0;
sprintf(str, " !C| !0%-66s !C|!0\n", buff);
printf(str);
}
...

Timeline
========

2004-04-02: Bug discovered
2004-07-14: Vendor notified (primemovr)
2004-07-16: Patch for format string bug
2004-07-22: public release

Discovered by
=============

Thomas Wana <greuff (at) void (dot) at [email concealed]>

Further research by
===================

Andi <andi (at) void (dot) at [email concealed]>

Credits
=======

void.at

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