Posts tagged: SSL Hack

Oct 24 2011

THC SSL DOS Tool Released

THC-SSL-DOS is a tool to verify the performance of SSL.

Establishing a secure SSL connection requires 15x more processing power on the server than on the client.

THC-SSL-DOS exploits this asymmetric property by overloading the server and knocking it off the Internet.

This problem affects all SSL implementations today. The vendors are aware of this problem since 2003 and the topic has been widely discussed.

This attack further exploits the SSL secure Renegotiation feature to trigger thousands of renegotiations via single TCP connection.

Download:
Windows binary : thc-ssl-dos-1.4-win-bin.zip
Unix Source : thc-ssl-dos-1.4.tar.gz

Use “./configure; make all install” to build.

Usage:
./thc-ssl-dos 127.3.133.7 443
Handshakes 0 [0.00 h/s], 0 Conn, 0 Err
Secure Renegotiation support: yes
Handshakes 0 [0.00 h/s], 97 Conn, 0 Err
Handshakes 68 [67.39 h/s], 97 Conn, 0 Err
Handshakes 148 [79.91 h/s], 97 Conn, 0 Err
Handshakes 228 [80.32 h/s], 100 Conn, 0 Err
Handshakes 308 [80.62 h/s], 100 Conn, 0 Err
Handshakes 390 [81.10 h/s], 100 Conn, 0 Err
Handshakes 470 [80.24 h/s], 100 Conn, 0 Err

Comparing Flood DDoS vs. SSL-Exhaustion Attack:
A traditional flood DDoS attack cannot be mounted from a single DSL connection.
This is because the bandwidth of a server is far superior to the bandwidth of a DSL connection: A DSL connection is not an equal opponent to challenge the bandwidth of a server.

This is turned upside down for THC-SSL-DOS: The processing capacity for SSL handshakes is far superior at the client side: A laptop on a DSL connection can challenge a server on a 30Gbit link.

Traditional DDoS attacks based on flooding are sub optimal: Servers are prepared to handle large amount of traffic and clients are constantly sending requests to the server even when not under attack.

The SSL-handshake is only done at the beginning of a secure session and only if security is required. Servers are _not_ prepared to handle large amount of SSL Handshakes.

The worst attack scenario is an SSL-Exhaustion attack mounted from thousands of clients (SSL-DDoS).

Tips & Tricks for WhiteHats:
– The average server can do 300 handshakes per second. This would require 10-25% of your laptops CPU.
– Use multiple hosts (SSL-DOS) if an SSL Accelerator is used.
– Be smart in target acquisition: The HTTPS Port (443) is not always the best choice. Other SSL enabled ports are more unlikely to use an SSL Accelerator (like the POP3S, SMTPS, … or the secure database port).

Counter measurements:
No real solutions exists. The following steps can mitigate (but not solve) the problem:
– Disable SSL-Renegotiation
– Invest into SSL Accelerator

Either of these countermeasures can be circumventing by modifying THC-SSL-DOS. A better solution is desireable. Somebody should fix this.

Sep 20 2011

Hackers Break SSL Encryption

SSL BreaksResearchers have discovered a serious weakness in virtually all websites protected by the secure sockets layer protocol that allows attackers to silently decrypt data that’s passing between a webserver and an end-user browser.

The vulnerability resides in versions 1.0 and earlier of TLS, or transport layer security, the successor to the secure sockets layer technology that serves as the internet’s foundation of trust. Although versions 1.1 and 1.2 of TLS aren’t susceptible, they remain almost entirely unsupported in browsers and websites alike, making encrypted transactions on PayPal, GMail, and just about every other website vulnerable to eavesdropping by hackers who are able to control the connection between the end user and the website he’s visiting.

At the Ekoparty security conference in Buenos Aires later this week, researchers Thai Duong and Juliano Rizzo plan to demonstrate proof-of-concept code called BEAST, which is short for Browser Exploit Against SSL/TLS. The stealthy piece of JavaScript works with a network sniffer to decrypt encrypted cookies a targeted website uses to grant access to restricted user accounts. The exploit works even against sites that use HSTS, or HTTP Strict Transport Security, which prevents certain pages from loading unless they’re protected by SSL.

The demo will decrypt an authentication cookie used to access a PayPal account, Duong said. Two days after this article was first published, Google released a developer version of its Chrome browser designed to thwart the attack.