[PRE-SA-2012-06] FreeRADIUS: Stack Overflow in TLS-based EAP Methods

[Timo Warns <Warns () Pre-Sense DE>]

PRE-CERT Security Advisory
==========================

* Advisory: PRE-SA-2012-06
* Released on: 10 September 2012
* Affected product: FreeRADIUS 2.1.10 - 2.1.12
* Impact: remote code execution
* Origin: specially crafted client certificates
* CVSS Base Score: 10
    Impact Subscore: 10
    Exploitability Subscore: 10
  CVSS Vector: (AV:N/AC:L/Au:N/C:C/I:C/A:C)
* Credit: Timo Warns (PRESENSE Technologies GmbH)
* CVE Identifier: CVE-2012-3547


Summary
-------

A stack overflow vulnerability has been identified in FreeRADIUS that allows to
remotely execute arbitrary code via specially crafted client certificates
(before authentication). The vulnerability affects setups using TLS-based EAP
methods (including EAP-TLS, EAP-TTLS, and PEAP).

FreeRADIUS defines a callback function cbtls_verify() for certificate
verification. The function has a local buf array with a size of 64
bytes. It copies the validity timestamp "not after" of a client
certificate to the buf array:

    asn_time = X509_get_notAfter(client_cert);
    if ((lookup <= 1) && asn_time && (asn_time->length < MAX_STRING_LEN)) {
        memcpy(buf, (char*) asn_time->data, asn_time->length);
        buf[asn_time->length] = '\0';

The MAX_STRING_LEN constant is defined to be 254. If asn_time->length is
greater than 64 bytes, but less than 254 bytes, buf overflows via the memcpy.

Depending on the stack layout chosen by the compiler, the vulnerability allows
to overflow the return address on the stack, which can be exploited for code
execution.


Solution
--------

The issue has been fixed in FreeRADIUS 2.2.0. Updates should be installed as
soon as possible.


References
----------

When further information becomes available, this advisory will be
updated. The most recent version of this advisory is available at:

http://www.pre-cert.de/advisories/PRE-SA-2012-06.txt


Contact
--------

PRE-CERT can be reached under precert () pre-secure de. For PGP key
information, refer to http://www.pre-cert.de/.

_______________________________________________
Full-Disclosure - We believe in it.
Charter: http://lists.grok.org.uk/full-disclosure-charter.html
Hosted and sponsored by Secunia - http://secunia.com/