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Category:   OS (UNIX)  >   OpenBSD Kernel Vendors:   OpenBSD
OpenBSD Protocol Flaw in SSL Renegotiation Lets Remote Users Conduct Man-in-the-Middle Attacks
SecurityTracker Alert ID:  1023243
SecurityTracker URL:
CVE Reference:   CVE-2009-3555   (Links to External Site)
Date:  Nov 26 2009
Impact:   Modification of user information
Fix Available:  Yes  Vendor Confirmed:  Yes  Exploit Included:  Yes  
Version(s): 4.5, 4.6
Description:   A vulnerability was reported in OpenBSD. A remote user can conduct a man-in-the-middle attack on SSL session renegotiation.

A remote user with the ability to conduct a man-in-the-middle attack can exploit a flaw in the underlying SSL/TLS protocol to inject arbitrary plain text into the exchange between the client and the server, with the arbitrary data as a prefix to the session.

The vulnerability resides in the TLS 1.0 or later and SSLv3 protocols.

The specific impact of this protocol flaw depends on the application using SSL/TLS.

Marsh Ray of PhoneFactor and Martin Rex independently reported this vulnerability.

[Editor's note: The flaw resides in the protocol and not in the protocol implementation. Some vendors are implementing a temporary workaround that prohibits session renegotiation until the protocol itself can be modified. Several protocol implementations are affected, including OpenSSL, GnuTLS, Network Security Services, and Java Secure Socket Extension.]

Impact:   A remote user can with the ability to conduct a man-in-the-middle attack can inject arbitrary plain text data into the exchange, preceding the session data.
Solution:   The vendor has issued a fix, available at:

Vendor URL: (Links to External Site)
Cause:   Authentication error

Message History:   None.

 Source Message Contents

Subject:  CVE-2009-3555: SSL/TLS renegotiation MITM vulnerability

The SSL/TLS protocol is subject to man-in-the-middle attacks
related to renegotiation (described in draft-ietf-tls-renegotiation-00)
allowing a MITM to inject chosen plaintext to the beginning of the
application data. Practical attacks exist against HTTPS and possibly
other protocols.

In -current, OpenSSL's ability to accept renegotiations has been
disabled by default. Patches are available for OpenBSD 4.6 and 4.5:

These are also available in the 4.5 and 4.6 -stable branches.


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