[UNIX] GNU Mailutils imap4d 'search' Format String Vulnerability

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  GNU Mailutils imap4d 'search' Format String Vulnerability
------------------------------------------------------------------------


SUMMARY

" <http://www.gnu.org/software/mailutils/mailutils.html> GNU Mailutils is 
a collection of mail-related utilities."

Lack of proper string validation allow attacker to execute arbitrary code 
using format string attack in GNU Mailutils imap4d.

DETAILS

Vulnerable Systems:
 * GNU Mailutils imap4d version 0.6

The imap4d server allows remote users to retrieve e-mail via the Internet  
Message Access Protocol, Version 4rev1 as specified in  
<ftp://ftp.rfc-editor.org/in-notes/rfc3501.txt> RFC3501. This is a 
client/server protocol supported by a large number of e-mail clients on 
multiple platforms.

The vulnerability specifically exists in the handling of SEARCH commands 
supplied by the remote user. If a search is made containing format 
specifiers (such as %p or %s), these will be interpreted by the server, 
and returned to the user.

Vulnerable Code:
search.c, lines 198-199:
rc = imap4d_search0 (arg, 0, buffer, sizeof buffer);
return util_finish (command, rc, buffer);

The vulnerability specifically occurs because the util_finish() function 
expects a format specifier in the 3rd argument, followed by any arguments 
to be formatted. Without a specifier, the function interprets the 3rd 
argument as a format specifier.

Exploitation could allow authenticated remote attackers to execute 
arbitrary commands on an affected system as the authenticated user. This 
may allow access to systems not intended to have interactive users, which 
could allow further compromise. Using format specifiers, it is possible to 
construct a sequence of commands that cause arbitrary values to be written 
to arbitrary locations, allowing arbitrary code execution.

Proof of Concept:
sh-2.05b$ netcat 192.168.0.1 143
* OK IMAP4rev1
1 LOGIN "user" "password"
1 OK LOGIN Completed
2 SELECT "inbox"
* 23 EXISTS
* 0 RECENT
* OK [UIDVALIDITY 1118516013] UID valididy status
* OK [UIDNEXT 24] Predicted next uid
* OK [UNSEEN 1] first unseen messsage
* FLAGS (\Answered \Flagged \Deleted \Seen \Draft)
* OK [PERMANENTFLAGS (\Answered \Deleted \Seen)] Permanent flags
2 OK [READ-WRITE] SELECT Completed
3 SEARCH TOPIC %08x.%08x.%08x.%08x
3 BAD SEARCH Unknown search criterion (near
00000040.6e6b6e55.206e776f.72616573)
4 SEARCH TOPIC %s%s%s
sh-2.05b$

The result of the 'SEARCH TOPIC %08x.%08x.%08x.%08x' command contains 
values from the error string supplied to the output function. (6e6b6e55 
converts to 'Unkn', 206e776f converts to 'own ' and 72616573 converts to 
'sear'.) By referencing the values after the fixed string in the error 
message, which are under control of the attacker, and using the '%n' 
format specifier, controllable values can be written to arbitrary memory 
locations, allowing execution of arbitrary code.

The '%s%s%s' format specifier attempts to treat the first 3 values 
(0x00000040, 0x6e6b6e55 and 0x206e776f) as strings, and causes an access 
violation error, terminating the server connection, dropping the user back 
into their shell. The main server is still active, as the server forks a 
new copy for each connection. This allows multiple exploitation attempts.

Vendor Status:
The vendor has release a patch available at:  
<http://savannah.gnu.org/patch/download.php?item_id=4407&item_file_id=5160> 
http://savannah.gnu.org/patch/download.php?item_id=4407&item_file_id=5160

Disclosure Timeline:
09/08/2005 - Initial vendor notification
09/09/2005 - Initial vendor response
09/09/2005 - Coordinated public disclosure


ADDITIONAL INFORMATION

The information has been provided by  
<mailto:idlabs-advisories@xxxxxxxxxxxxxxxxxx> iDEFENSE Labs Security 
Advisories .
The original article can be found at:  
<http://www.idefense.com/application/poi/display?id=303&type=vulnerabilities&flashstatus=true>
 
http://www.idefense.com/application/poi/display?id=303&type=vulnerabilities&flashstatus=true
The vendor advisory can be found at:  
<http://savannah.gnu.org/patch/index.php?func=detailitem&item_id=4407> 
http://savannah.gnu.org/patch/index.php?func=detailitem&item_id=4407



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