[squid-dev] [PATCH] TLS: Disable client-initiated renegotiation

[Amos Jeffries]

This gets a +1 from me.

NP: It seems a little bit odd to be setting a flag this way rather than
with flags= like all the others. However it needs to be at a default to
begin with and then set definitively OFF only after the first handshake
completes.

Christos, do you agree?

Amos


On 5/06/2015 6:51 a.m., Paulo Matias wrote:
> Hi all,
> 
> This patch disables client-initiated renegotiation, mitigating a DoS attack
> which might be possible with some builds of the OpenSSL library.  We have been
> warned about this when testing our service with the Qualys SSL Test
> (https://www.ssllabs.com/ssltest) back when it was running in a Debian wheezy
> system. Further information is available at:
> https://community.qualys.com/blogs/securitylabs/2011/10/31/tls-renegotiation-and-denial-of-service-attacks
> Our solution is similar to the one adopted in pureftpd:
> https://github.com/jedisct1/pure-ftpd/blob/549e94aaa093a48622efd6d91fdfb3a4236c13f4/src/tls.c#L106
> 
> This was previously posted to squid-users, but modified since then to implement
> Amos's suggestions:
> 
>> * please avoid #ifdef and #ifndef in new code.
>> - use #if defined() style instead.
>> * please wrap the entire ssl_info_cb() definition in the #if
>> conditionals and the appropriate calling lines.
> 
> We welcome any additional suggestions or comments.
> 
> Best regards,
> Paulo Matias
> 
> 
> -------------- next part --------------
> === modified file 'src/ssl/support.cc'
> --- src/ssl/support.cc	2015-06-03 10:42:08 +0000
> +++ src/ssl/support.cc	2015-06-04 12:59:30 +0000
> @@ -823,12 +823,28 @@
>      return dh;
>  }
>  
> +#if defined(SSL3_FLAGS_NO_RENEGOTIATE_CIPHERS)
> +static void
> +ssl_info_cb(const SSL *ssl, int where, int ret)
> +{
> +    (void)ret;
> +    if ((where & SSL_CB_HANDSHAKE_DONE) != 0) {
> +        // disable renegotiation (CVE-2009-3555)
> +        ssl->s3->flags |= SSL3_FLAGS_NO_RENEGOTIATE_CIPHERS;
> +    }
> +}
> +#endif
> +
>  static bool
>  configureSslContext(SSL_CTX *sslContext, AnyP::PortCfg &port)
>  {
>      int ssl_error;
>      SSL_CTX_set_options(sslContext, port.sslOptions);
>  
> +#if defined(SSL3_FLAGS_NO_RENEGOTIATE_CIPHERS)
> +    SSL_CTX_set_info_callback(sslContext, ssl_info_cb);
> +#endif
> +
>      if (port.sslContextSessionId)
>          SSL_CTX_set_session_id_context(sslContext, (const unsigned char *)port.sslContextSessionId, strlen(port.sslContextSessionId));
>  
> @@ -1045,6 +1061,10 @@
>  
>      SSL_CTX_set_options(sslContext, Ssl::parse_options(options));
>  
> +#if defined(SSL3_FLAGS_NO_RENEGOTIATE_CIPHERS)
> +    SSL_CTX_set_info_callback(sslContext, ssl_info_cb);
> +#endif
> +
>      if (*cipher) {
>          debugs(83, 5, "Using chiper suite " << cipher << ".");
>  
> 
> 
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