bugtraq - [PRE-SA-2012-07] hostapd: Missing EAP-TLS message length validation

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Message-ID: <20121008125657.GA23154@pre-sense.de>
Date: Mon, 8 Oct 2012 14:56:57 +0200
From: Timo Warns <Warns@...-Sense.DE>
To: full-disclosure@...ts.grok.org.uk, bugtraq@...urityfocus.com
Subject: [PRE-SA-2012-07] hostapd: Missing EAP-TLS message length validation

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

* Advisory: PRE-SA-2012-07
* Released on: 8 October 2012
* Affected product: Hostapd 0.6 - 1.0
* Impact: denial of service
* Origin: specially crafted EAP-TLS messages
* CVSS Base Score: 7.8
    Impact Subscore: 6.9
    Exploitability Subscore: 10
  CVSS Vector: (AV:N/AC:L/Au:N/C:N/I:N/A:C)
* Credit: Timo Warns (PRESENSE Technologies GmbH)
* CVE Identifier: CVE-2012-4445

Summary
-------

The internal EAP authentication server of hostapd does not sufficiently
validate the message length field of EAP-TLS messages, which can be
exploited for a denial-of-service via specially crafted EAP-TLS messages
(before authentication).

Hostapd has a function eap_server_tls_process_fragment() used by its
internal EAP authentication server for handling fragmented EAP-TLS
messages. The function (indirectly) calls wpabuf_overflow() aborting
the application in case of potential buffer overflows. Such a situation
can be triggered by an attacker sending an EAP-TLS message with

    a) the "More Fragments" flag set and
    b) an "TLS Message Length" value that is smaller than the size of
       the "TLS Data" field.

The vulnerability can be exploited only if hostapd is configured to use
its internal EAP authentication server, either directly for IEEE 802.11x
or when using hostapd as a RADIUS authentication server. 

Affected is hostapd in versions 0.6 - 1.0. The issue was introduced with
commit
http://hostap.epitest.fi/gitweb/gitweb.cgi?p=hostap.git;a=commitdiff;h=34f564dbd5168626da55a7119b04832e98793160

Solution
--------

A patch is available at
http://w1.fi/gitweb/gitweb.cgi?p=hostap.git;a=commitdiff;h=586c446e0ff42ae00315b014924ec669023bd8de

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-2012-07.txt

Contact
--------

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