Openswan XAUTH/PAM Buffer Overflow Vulnerability

iDEFENSE Security Advisory 01.26.05
www.idefense.com/application/poi/display?id=190&type=vulnerabilities
January 26, 2005

I. BACKGROUND

Openswan is an open source implementation of IPSEC for the Linux 
Operating System. Openswan is based on the discontinued FreeS/WAN 
project.

More information is available on the vendor's website: 
http://www.openswan.org/

II. DESCRIPTION

Remote exploitation of a stack based buffer overflow vulnerability in 
Xelerance Corp.'s Openswan could allow attackers to execute arbitrary 
code. 

The vulnerability specifically exists due to a lack of bounds checking 
in the pluto application when Openswan is compiled with XAUTH and PAM 
support. The get_internal_addresses() function in 
programs/pluto/xauth.c allocates a small character array and copies an 
overly long user controlled buffer into the array as seen below. The 
resulting stack overflow may be leveraged to execute arbitrary code 
with permissions of the pluto process. 

in programs/pluto/id.h:

47:  #define IDTOA_BUF  512

in programs/pluto/xauth.c:

148: #ifdef XAUTH_USEPAM
149:  int retval;
150:  char str[48];
151: #endif
...
169: if(retval == PAM_SUCCESS)
170: {
171:   char buf[IDTOA_BUF];
...
185:   sprintf(str,"ID=%s", buf);

III. ANALYSIS

Successful exploitation of the vulnerability can allow remote attackers 
to execute code with privileges of the pluto process. Exploitation in 
the wild will be limited due to the fact that Openswan would need to be 
compiled with XAUTH and PAM options enabled which are both disabled by 
default. In addition, exploitation occurs after an IKE Phase-1 Security 
Association (SA) has been established which requires authentication of 
a shared key and the supplied client certificate, further reducing the 
impact of this vulnerability. 

IV. DETECTION

iDEFENSE has confirmed that Openswan 2.2.0 is vulnerable. All previous 
versions of Openswan also contain the vulnerable code.

V. WORKAROUND

The XAUTH and PAM configuration options can be found in Makefile.inc in 
the Openswan source tree. Disable both configuration options or apply 
the following vendor-supplied patch:

Index: xauth.c
===================================================================
RCS file: /xelerance/master/openswan-2/programs/pluto/xauth.c,v
retrieving revision 1.35
diff -u -p -u -r1.35 xauth.c
- --- xauth.c  30 Nov 2004 15:30:24 -0000  1.35
+++ xauth.c  8 Jan 2005 02:25:35 -0000
@@ -187,7 +187,7 @@ int get_internal_addresses(struct connec  {  
 #ifdef XAUTH_USEPAM
     int retval;
- -    char str[48];
+    char str[IDTOA_BUF+sizeof("ID=")+2];
 #endif

 #ifdef NAT_TRAVERSAL /* only NAT-T code lets us do virtual ends */ 
@@ -222,7 +222,7 @@ int get_internal_addresses(struct connec
               memmove(buf, c1+3,
strlen(c1) + 1 - 3);
             }
           }
- -          sprintf(str,"ID=%s", buf);
+          snprintf(str, sizeof(str), "ID=%s", buf);
           pam_putenv(con->pamh,str);
           pam_open_session(con->pamh,0);
         }


VI. VENDOR RESPONSE

The vendor has addressed this vulnerability in newly released Openswan
packages. Users should upgrade to Openswan 1.0.9 or Openswan 2.3.0
depending on their current configuration. New packages are available
from the following link:

http://www.openswan.org/code/

VII. CVE INFORMATION

A Mitre Corp. Common Vulnerabilities and Exposures (CVE) number has not 
been assigned yet.

VIII. DISCLOSURE TIMELINE

01/06/2005  Initial vendor notification
01/06/2005  Initial vendor response
01/26/2005  Public disclosure

IX. CREDIT

The discoverer of this vulnerability wishes to remain anonymous.

Get paid for vulnerability research
http://www.idefense.com/poi/teams/vcp.jsp

X. LEGAL NOTICES

Copyright (c) 2005 iDEFENSE, Inc.

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Disclaimer: The information in the advisory is believed to be accurate
at the time of publishing based on currently available information. Use
of the information constitutes acceptance for use in an AS IS condition.
There are no warranties with regard to this information. Neither the
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this information.