[Openswan dev] ANNOUNCE: Security Advisory CAN-2004-590 - X.509 Digital Certificate Handling

[Ken Bantoft]

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Certificate chain authentication in Openswan pluto

Published:
    NOT YET PUBLISHED 
Revision of advisory:
    1.0 
Location
    http://www.openswan.org/support/vuln/can-2004-0590 
CVE:
    CAN-2004-0590 

This problem was discovered by Thomas Walpuski of IKS GmbH Jena.

No exploit is known to be available.
Affected system(s)
KNOWN VULNERABLE:

    * superfreeswan 1.x (all revisions with X.509 patch)
    * openswan 1.x < 1.0.6
    * openswan 2.x < 2.1.4
    * strongSwan <2.1.3
    * Any version of FreeS/WAN 1.x with X.509 patch < 0.9.41
    * Any version of FreeS/WAN 2.x with X.509 patch < 1.6.1 

To be vulnerable one must be using X.509/pkix key material that is 
authenticated with a CA.

Self-signed certificates that are loaded from disk are not affected, nor 
are PSK, RSA (from disk or DNS) or Opportunistic Encryption.
Summary

Given a policy exists that is based upon X.509 DN identities that permits 
identity "B" to establish some kind of tunnel with a gateway or end 
system, and B's credentials may be attested to by a trusted Certificate 
Authority "A".

This vulnerability permits a malicious end-system to make up their own 
Certificate Authority A' such that it has issuer=B, and subject=A', 
followed by a self-signed end-certificate with issuer B and subject B. 
When presented, this certificate chain will validate permitting the 
attacker to impersonate B.

The attacker must know a valid DN B to use, and must match the policy 
which B is authorized to use. As openswan does not use aggressive mode by 
default, (and does not include it in version 2), it is not possible to 
learn identity B by passive eavesdropping. B may be guessed, determined by 
social engineering, or may be retrieved by an active man-in-the-middle 
attack.


Vendor status and information

Openswan
    http://www.openswan.org/ 
StrongSwan
    http://www.strongswan.org/ 
FreeS/WAN
    http://www.freeswan.org/ - no longer active 

All vendors have been notified and have provided patched versions.

Solution

    * a) apply patch or upgrade to >=1.0.5 or >=2.1.3 versions of Openswan.
	Patch URL: http://anoncvs.openswan.org/cgi-bin/viewcvs.cgi/openswan-1/pluto/x509.c.diff?r1=1.23&r2=1.25&diff_format=u
    * b) only accept certificates for the remote system which are signed 
by the same CA as the local system. This can be done by setting "rightca=%same". 

Detailed analysis

The mechanism which is used to authenticate the certificate chain 
presented by an end-system errorneously sees the issuer=B/subject=B as a 
trusted root CA when it has not yet been verified.

Openswan test case fail-x509-09 provides a more detailed analysis.
Contact Information

   Xelerance Corporation
   Email:  vuln at xelerance.com
   Web:    http://www.xelerance.com/
   Phone:  +1 905 257 3392

About CAN

The Common Vulnerabilities and Exposures (CVE) project has assigned the 
name CAN-2004-0590 to this issue. This is a candidate for inclusion in the 
CVE list (http://cve.mitre.org), which standardizes names for security 
problems. 



- -- 
Ken Bantoft			VP Business Development
ken at xelerance.com		Xelerance Corporation
sip://toronto.xelerance.com	http://www.xelerance.com

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