THC SSL Renegotiation DoS Tool for SMTP STARTTLS

The so called Secure Client-Initiated Renegotiation function of SSL/TLS suffers from a possible DoS danger because it burdens the server’s CPU orders of magnitude more than the client’s, who initiates it. Because of that, Client-Initiated Renegotiation is nowadays disabled by default in virtually all widely used SSL/TLS implementations.

However, I noticed that it seems to be still enabled by default on the postfix SMTP daemon including recent releases (postfix 2.6.6) and openssl (1.0.1j) versions and there appears to be no way of disabling it in the configuration. Since I already used the thc ssl dos tool which exploits this vulnerability in previous penetration tests on webservers, I thought it would be nice if it worked with SMTP mailservers supporting STARTTLS as well.

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MS14-066 / CVE-2014-6321

[Update 2014/11/18]
Details of the vulnerability have been released. If you still haven’t patched internet-facing Windows systems, do it ASAP.

After all the (well, partly justified) rage and criticism openssl or free/open source software in general received recently with fuckups like the heartbleed, changecipherspec or shellshock vulnerabilities, it’s been about time for a major vulnerability of a similar scale in our most beloved Windows systems.

This security update resolves a privately reported vulnerability in the Microsoft Secure Channel (Schannel) security package in Windows. The vulnerability could allow remote code execution if an attacker sends specially crafted packets to a Windows server.
The security update addresses the vulnerability by correcting how Schannel sanitizes specially crafted packets.Mitigating Factors
Microsoft has not identified any mitigating factors for this vulnerability.
Microsoft has not identified any workarounds for this vulnerability.
FAQWhat might an attacker use the vulnerability to do?
An attacker who successfully exploited this vulnerability could run arbitrary code on a target server.

How could an attacker exploit the vulnerability?
An attacker could attempt to exploit this vulnerability by sending specially crafted packets to a Windows server.

What systems are primarily at risk from the vulnerability?
Server and workstation systems that are running an affected version of Schannel are primarily at risk.

Oh? What do we have here? Is this an unauthenticated remote code execution vulnerability in the schannel Windows SSL/TLS library, affecting every Windows version since 2003 (probably XP and maybe 2000 as well)?. Let the SSL/TLS fuzzing begin; it’s probably only a matter of time until a PoC exploit is published (if it isn’t already in some secret channels, this was “privately reported”). Patch that stuff now.
Incidentally, this update also adds two new TLS 1.2 cipher suites to the schannel repository.