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Operating Systems Linux Red Hat SSL/TLS renegotiation DoS -how to disable? Is it advisable to disable? Post 302567266 by manalisharmabe on Sunday 23rd of October 2011 03:09:19 PM
Old 10-23-2011
Question SSL/TLS renegotiation DoS -how to disable? Is it advisable to disable?

Hi all Expertise,

I have following issue to solve,

SSL / TLS Renegotiation DoS (low) 222.225.12.13

Ease of Exploitation Moderate
Port 443/tcp
Family Miscellaneous
Following is the problem description:------------------
Description The remote service encrypts traffic using TLS / SSL and permits clients to
renegotiate
connections. The computational requirements for renegotiating a connection are
asymmetrical between the client and the server, with the server performing several times
more work. Since the remote host does not appear to limit the number of renegotiations
for a single TLS / SSL connection, this permits a client to open several simultaneous
connections and repeatedly renegotiate them, possibly leading to a denial of service
condition.

Impact Over All Impact - PARTIAL
Confidentiality Impact - NONE
Integrity Impact - NONE
Availability Impact - PARTIAL
Recommendations Contact the vendor for specific patch information. It is possible to temporarily workaround the flaw by implementing the following workaround: Disable TLS/SSL renegotiation.

My queries are-
1.How to diasble SSL/TLS Renegotitation ;what we modify in ssl.conf to disable it?
2. Is it advisable to disable it?
2a.If SSL/TLS Renegotitation is disabled then will it affect some operation?
Please guide me, I have googled on this issue but still not sure about mentioned issue's solution.

Please Guide me.
Thanks in Advance!

ONE MORE THING THE SSL CERTIFICATE HAS ALREADY EXPIRED.

So final question how to block a client opening several simultaneous connections and repeatedly renegotiate them, possibly leading to a denial of service condition?

Last edited by manalisharmabe; 10-23-2011 at 04:56 PM..
 

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SSL_connect(3SSL)						      OpenSSL							 SSL_connect(3SSL)

NAME
SSL_connect - initiate the TLS/SSL handshake with an TLS/SSL server SYNOPSIS
#include <openssl/ssl.h> int SSL_connect(SSL *ssl); DESCRIPTION
SSL_connect() initiates the TLS/SSL handshake with a server. The communication channel must already have been set and assigned to the ssl by setting an underlying BIO. NOTES
The behaviour of SSL_connect() depends on the underlying BIO. If the underlying BIO is blocking, SSL_connect() will only return once the handshake has been finished or an error occurred. If the underlying BIO is non-blocking, SSL_connect() will also return when the underlying BIO could not satisfy the needs of SSL_connect() to continue the handshake, indicating the problem by the return value -1. In this case a call to SSL_get_error() with the return value of SSL_connect() will yield SSL_ERROR_WANT_READ or SSL_ERROR_WANT_WRITE. The calling process then must repeat the call after taking appropriate action to satisfy the needs of SSL_connect(). The action depends on the underlying BIO. When using a non-blocking socket, nothing is to be done, but select() can be used to check for the required condition. When using a buffering BIO, like a BIO pair, data must be written into or retrieved out of the BIO before being able to continue. RETURN VALUES
The following return values can occur: <0 The TLS/SSL handshake was not successful, because a fatal error occurred either at the protocol level or a connection failure occurred. The shutdown was not clean. It can also occur of action is need to continue the operation for non-blocking BIOs. Call SSL_get_error() with the return value ret to find out the reason. 0 The TLS/SSL handshake was not successful but was shut down controlled and by the specifications of the TLS/SSL protocol. Call SSL_get_error() with the return value ret to find out the reason. 1 The TLS/SSL handshake was successfully completed, a TLS/SSL connection has been established. SEE ALSO
SSL_get_error(3), SSL_accept(3), SSL_shutdown(3), ssl(3), bio(3), SSL_set_connect_state(3), SSL_do_handshake(3), SSL_CTX_new(3) 1.0.1e 2014-08-06 SSL_connect(3SSL)
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