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SSLstrip. Stepan Shykerynets. http://wisc.org.ua / 23.03.2013. http://wisc.org.ua / 23.03.2013. http://wisc.org.ua / 23.03.2013. http://wisc.org.ua / 23.03.2013. Attention. !. http://wisc.org.ua / 23.03.2013. http://wisc.org.ua / 23.03.2013. http://wisc.org.ua / 23.03.2013.
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SSLstrip StepanShykerynets http://wisc.org.ua/ 23.03.2013
Attention ! http://wisc.org.ua/ 23.03.2013
Private / Public key CLIENT SERVER Private key Public key http://wisc.org.ua/ 23.03.2013
Private / Public key CLIENT SERVER Public key CA Private key Public key http://wisc.org.ua/ 23.03.2013
Private / Public key CLIENT SERVER Public key Private key Public key CA http://wisc.org.ua/ 23.03.2013
Private / Public key http://wisc.org.ua/ 23.03.2013
SSL And Certificate Chaining http://wisc.org.ua/ 23.03.2013
Certificate • X509 Certificate version serial number issuer validity subject public key • Signature algorithm • Signature http://wisc.org.ua/ 23.03.2013
Certificate Chaining CA Certificate Embedded in browser. All powerful. Certifies that a site certificate is authentic. Site Certificate Identifies a particular URL. Is known to be authentic based on CA Certificate's signature. http://wisc.org.ua/ 23.03.2013
Certificate Chaining CA Certificate Embedded in browser. All powerful. Certifies that a site certificate is authentic. Intermediate CA Not embedded in browser. Still sort of all-powerful. Certifies that a site certificate is authentic. Site Certificate Identifies a particular URL. Is known to be authentic based on CA Certificate's signature. http://wisc.org.ua/ 23.03.2013
Certificate Chaining VeriSign Intermediate CA Facebook.com http://wisc.org.ua/ 23.03.2013
Certificate Chains Can Be > 3 VeriSign Intermediate CA Intermediate CA Facebook.com http://wisc.org.ua/ 23.03.2013
How do we validate these things? • Verify that the leaf node has the name of the site you're connecting to. • Verify that the leaf node hasn't expired. • Check the signature. • If the signing certificate is in our list of root CA's, stop. • Otherwise, move one up the chain and repeat. http://wisc.org.ua/ 23.03.2013
Very tempting to use a simple recursive function. Everyone focuses on the signature validation. The result of a naive attempt at validation is a chain that is complete, but nothing more. http://wisc.org.ua/ 23.03.2013
What if … VeriSign Intermediate CA Intermediate CA hack.org http://wisc.org.ua/ 23.03.2013
What if … VeriSign Intermediate CA Intermediate CA hack.org Facebook.com http://wisc.org.ua/ 23.03.2013
What they say : • Verify that the leaf node has the name of the site you're connecting to. • Verify that the leaf node hasn't expired. • Check the signature. • If the signing certificate is in our list of root CA's, stop. • Otherwise, move one up the chain and repeat. http://wisc.org.ua/ 23.03.2013
But … • All the signatures are valid • Nothing has expired • The chain is in fact • The root CA is embedded in the browser and trusted http://wisc.org.ua/ 23.03.2013
The missing piece http://wisc.org.ua/ 23.03.2013
The missing piece ! http://wisc.org.ua/ 23.03.2013
The missing piece http://wisc.org.ua/ 23.03.2013
Most CA's didn't explicitly set basic Constraints: CA=FALSE • A lot of web browsers and other SSL implementations didn't bother to check it, whether the field was there or not • Any one with a valid leaf node certificate could create and sign a leaf node certificate for any other domain. http://wisc.org.ua/ 23.03.2013
But we have one problem http://wisc.org.ua/ 23.03.2013
Smart browsers http://wisc.org.ua/ 23.03.2013
People are … http://wisc.org.ua/ 23.03.2013
People are … LAZY http://wisc.org.ua/ 23.03.2013
http://...https://... http://wisc.org.ua/ 23.03.2013
SSLsniff http://wisc.org.ua/ 23.03.2013
SSLsniff • Intercept a connection from the client side. • Generate a certificate for the site it is connecting to. • Sign in with any random valid leaf node certificate. • Pass that certificate chain to the client. • Make normal SSL connection to the server. • Pass data between client and server, decrypting and encrypting on each end. http://wisc.org.ua/ 23.03.2013
Web browsing • SSL is almost never encountered directly. • It is either encountered as a result of: A 302 redirect from HTTP URL to an HTTPS URL. An HTTPS link that a user click on from an HTTP page. http://wisc.org.ua/ 23.03.2013
SSLstrip • Watch HTTP traffic go by. • Switch <a href="https://> to <a href="http://> and keep a map of what you've changed. • Switch Location: https:// to Location: http:// and keep a map of what you've changed. http://wisc.org.ua/ 23.03.2013
SSLstrip • Watch HTTP traffic go by. • When we seen an HTTP request for URL that we've stripped, proxy that out as HTTPS to the server. • Watch the HTTPS traffic go by, log everything that we want, and keep a map of all relative, CSS and JS links that go by. http://wisc.org.ua/ 23.03.2013
SSLstrip • The server never knows the difference. Everything looks secure on their end. • The client doesn't display any of the disastrous warnings that we want to avoid. • We see all the traffic. http://wisc.org.ua/ 23.03.2013
Let's simplify it… http://wisc.org.ua/ 23.03.2013
Time to action http://wisc.org.ua/ 23.03.2013
BackTrack : Giving Machine Guns to Monkeys since 2006 http://wisc.org.ua/ 23.03.2013
Tools • SSLstrip • ARPspoof • Ettercap http://wisc.org.ua/ 23.03.2013
Commands • #bt echo "1" > /proc/sys/net/ipv4/ip_forward • # btiptables -t nat -A PREROUTING -p tcp --destination-port 80 -j REDIRECT --to-port 10000 • #btsslstrip -a -l 10000 -w log.txt –f • # arpspoof -i <yourNetworkdDevice> -t <yourTarget> <theRoutersIpAddress> • # ettercap -T –q –i <yourNetworkdDevice> http://wisc.org.ua/ 23.03.2013
Protection • Google services • High protection network equipment • Checking site certificates http://wisc.org.ua/ 23.03.2013
StepanShykerynets SShykerynets@gmail.com
