OSEC

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[OpenCA Advisory] Vulnerability in signature verification

From: Michael Bell (michael.bellcms.hu-berlin.de)
Date: Fri Jan 16 2004 - 09:04:49 CST


OpenCA Security Advisory [16 January 2004]

Vulnerability in signature validation
=====================================

A flaw in OpenCA before version 0.9.1.7 could cause OpenCA to accept a
signature from a certificate if the certificate's chain is trusted by
the chain directory of OpenCA. This means that a certificate from
another PKI can authorize operations on the used PKI if the chain of the
used signature certifcate can establish a trust relationship to the
actually used PKI.

Alexandru Matei found the bug during a source code verification.
Alexandru Matei and Michael Bell of the OpenCA core team fixed the
problem for OpenCA 0.9.1 and the CVS HEAD.

Vulnerability
-----------------

OpenCA has a library for common crypto operations - crypto-utils.lib.
This library includes a function to check a signature
(libCheckSignature). The function load the used signature certificate
from OpenCA's database and finally ensures that the used signature
certificate is identical with the certificate in the database.

The comparison of the certificate in the database and the certificate
of the signer was only performed on base of the serial of the
certificate. The design of the function can cause the acceptance
of a signature if the chain of the signature can create a
trustrelationship to the chain directory of OpenCA and a certificate
with a matching serial exists in the used PKI.

Who is affected?
------------------

All version of OpenCA including 0.9.1.6. A security risk is present for
people who are using digital signatures to secure approved requests
or role based access control (RBAC).

Recommendations
-----------------

Upgrade to 0.9.1.7 and use newer snapshots than
openca-SNAP-20040114.tar.gz. You can fix the problem by yourself too
with the included patch. The original file which we used to create
the diff is from OpenCA 0.9.1.6.

-----BEGIN PATCH-----
--- src/common/lib/functions/crypto-utils.lib 2004-01-15
12:10:45.000000000 +0100
+++ src/common/lib/functions/crypto-utils.lib.new 2004-01-15
12:10:06.000000000 +0100
-201,7 +201,7
                                                "__ERRVAL__",
$OpenCA::X509::errval);
                         return undef;
                 }
- last if ( $tmpCert->getSerial() eq $sigCert->getSerial() );
+ last if ( $tmpCert->getPEM() eq $sigCert->getPEM() );
                 $sigCert = undef;
         }

-----END PATCH-----

References
------------

The Common Vulnerabilities and Exposures project (cve.mitre.org) has
assigned the name CAN-2004-0004 to this issue.

http://cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2004-0004

URL for this Security Advisory:
http://www.openca.org/news/CAN-2004-0004.txt