SSL, HSTS and other stuff with two eSSes
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SSL is widely accepted as a technology that protects site users from certain attacks. But does it really protect them? Are we deploying it right? Probably not. I will show you why Presented at Confraria Security & IT, 22/06/11, Lisbon. note: this is the second version of this presentation. Please see the other presentations for updated content.
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SSL, HSTS and other stuff with two eSSes
- 1. SSL, HSTS and other stuff with two eSSes Versão 1.1 - 22/06/2011 Confraria Security & IT Tiago Mendo -‐ ,ago.mendo@telecom.pt
- 2. Summary • History – SSL – TLS – SSL vs TLS • Protocol – Objec9ves – Applica9ons • How it works -‐ the 2 minutes version • How it works -‐ the 30 minutes version – Cer9ficate valida9on – Cer9ficate revoca9on check – Cer9ficate chain of trust check – Fetching content – Redirec9ng from HTTP to HTTPS – Full HTTPS browsing – Mixed content browsing • Recommenda9ons • Conclusions • Ques9ons SAPO Websecurity Team 2
- 3. History > SSL • SSL -‐ Secure Sockets Layer • 1994 -‐ SSL 1.0 created by Netscape, never released • 1995 -‐ SSL 2.0 released in Netscape Navigator 1.1. Mul9ple security flaws found • 1996 -‐ SSL 3.0 released SAPO Websecurity Team 3
- 4. History > TLS • TLS -‐ Transport Layer Security • 1999 -‐ TLS 1.0 defined in RFC 2246, using SSL 3.0 as basis • 2006 -‐ TLS 1.1 defined in RFC 4346 • 2008 -‐ TLS 1.2 defined in RFC 5246 SAPO Websecurity Team 4
- 5. History > SSL vs TLS SSL TLS 1.0 2.0 3.0 (3.1) 1.0 (3.2) 1.1 (3.3) 1.2 • SSL 3.0 and TLS 1.0 are equivalent in security, but incompa9ble • “Everybody knows SSL. TLS is more technically accurate but sounds like a cable TV network or a disease" SAPO Websecurity Team 5
- 6. Protocol > Objectives • Why SSL? SAPO Websecurity Team 6
- 7. Protocol > Objectives • Why SSL? • To protect the communica9ons between two hosts: – content confiden9ality – integrity – authen9city SAPO Websecurity Team 6
- 8. Protocol > Objectives • Why SSL? • To protect the communica9ons between two hosts: – content confiden9ality – integrity – authen9city • Host iden9ty is not protected (requires IPSEC) • Normally only the server is authen9cated SAPO Websecurity Team 6
- 9. Protocol > Applications Applica,on HTTP Transport TCP Network IP Data link 802.11 -‐ WLAN Physical Air SAPO Websecurity Team 7
- 10. Protocol > Applications Applica,on HTTP HTTP / SSL Transport TCP TCP Network IP IP Data link 802.11 -‐ WLAN 802.11 -‐ WLAN Physical Air Air SAPO Websecurity Team 7
- 11. Protocol > Applications HTTP Applica,on HTTP HTTP / SSL SSL Transport TCP TCP TCP Network IP IP IP Data link 802.11 -‐ WLAN 802.11 -‐ WLAN 802.11 -‐ WLAN Physical Air Air Air SAPO Websecurity Team 7
- 12. Protocol > Applications HTTP Applica,on HTTP HTTP / SSL SSL Transport TCP TCP TCP Network IP IP IP Data link 802.11 -‐ WLAN 802.11 -‐ WLAN 802.11 -‐ WLAN Physical Air Air Air • On top of any Transport layer (including UDP) • Used with any Applica9on layer protocol • HTTP, SMTP, XMPP, SIP, etc. • Used in OpenVPN SAPO Websecurity Team 7
- 13. How it works - the 2 minutes version • Type hdps://www.facebook.com and hit enter SAPO Websecurity Team 8
- 14. How it works > Traffic without SSL SAPO Websecurity Team 9
- 15. How it works > Traffic with SSL SAPO Websecurity Team 10
- 16. How it works - the 30 minutes version • Type hdps://www.facebook.com and hit enter • Browser connects to www.facebook.com:443 • SSL handshake is ini9ated • Server sends its X.509 cer9ficate to the client • The client starts the valida9on process SAPO Websecurity Team 11
- 17. How it works > Certificate validation • CN matches URL • For each cert. in the chain – Has not expired – Was not revoked – Was emided by a trusted CA SAPO Websecurity Team 12
- 18. How it works > Certificate validation • CN matches URL • For each cert. in the chain – Has not expired – Was not revoked – Was emided by a trusted CA SAPO Websecurity Team 13
- 19. How it works > Certificate validation • CN matches URL • For each cert. in the chain – Has not expired – Was not revoked – Was emided by a trusted CA SAPO Websecurity Team 14
- 20. How it works > Certificate validation • CN matches URL • For each cert. in the chain – Has not expired – Was not revoked – Was emided by a trusted CA SAPO Websecurity Team 15
- 21. How it works > Certificate revocation check • CRL -‐ Cer9ficate Revoca9on List • The cer9ficate specifies a CRL URL • The CRL is a list of revoked serial numbers • Answer can be cached for a few months – period defined by the CA • The CRL can be very large: enter OCSP – expired certs. are removed from the CRL SAPO Websecurity Team 16
- 22. How it works > Certificate revocation check • OCSP -‐ Online Cer9ficate Status Protocol • The cer9ficate specifies a OCSP server • Browser asks the server if a specific cert. is s9ll valid • Answer can be cached for a few days – period defined by the CA • A cert. can specify both the CRL and OCSP SAPO Websecurity Team 17
- 23. How it works > Certificate revocation check • What can go wrong? SAPO Websecurity Team 18
- 24. How it works > Certificate revocation check • What can go wrong? • CRL and OCSP servers can be unreachable – Browsers will allow user to con9nue – You may or may not be warned about this – Moxie Marlinspike found that OCSP “try again” message (error code 3) is not signed – Adack: MiTM with a revoked cert. and reply 3 to the OCSP requests. SAPO Websecurity Team 18
- 25. How it works > Certificate revocation check • How to mi9gate this problem? SAPO Websecurity Team 19
- 26. How it works > Certificate revocation check • How to mi9gate this problem? • OCSP Stapling -‐ Kerberos style 9cket – Cert. owner frequently asks the OCSP for a 9cket – Ticket says “I, CA guarantee with my signature that this cer9ficate is valid for a few hours” – Site presents this 9cket to reques9ng browser • Fallback to OCSP • Support: Chrome on Windows Vista or higher SAPO Websecurity Team 19
- 27. How it works > Certificate revocation check • How to mi9gate this problem? SAPO Websecurity Team 20
- 28. How it works > Certificate revocation check • How to mi9gate this problem? • CRL and OCSP cache SAPO Websecurity Team 20
- 29. How it works > Certificate revocation check • How to mi9gate this problem? • CRL and OCSP cache • Which introduces another problem – If a cert. is compromised, there may a significant window of vulnerability (months for a CRL) – Remember the Comodo RA compromise? – 9 certs. were issued to 7 domains – certs. were revoked in 15 minutes – Browser vendors immediately issued browser updates SAPO Websecurity Team 20
- 30. How it works > Certificate validation • CN matches URL • For each cert. in the chain – Has not expired – Was not revoked – Was emi@ed by a trusted CA SAPO Websecurity Team 21
- 31. How it works > Certificate chain of trust check • The server sends the whole cer9ficate chain • For each cert. in the chain verify – is properly signed by the CA cer9ficate immediately higher in the hierarchy – last cer9ficate is explicitly trusted by the browser, so no signature verifica9on is done SAPO Websecurity Team 22
- 32. How it works > Certificate chain of trust check • What can go wrong? SAPO Websecurity Team 23
- 33. How it works > Certificate chain of trust check SAPO Websecurity Team 24
- 34. How it works > Certificate chain of trust check • What can go wrong? • The browser does not know the root CA – can happen if you are using an old browser/device SAPO Websecurity Team 25
- 35. How it works > Certificate chain of trust check • What can go wrong? • The browser does not know the root CA – can happen if you are using an old browser/device • How to mi9gate this problem? • Mul9-‐roo9ng CAs – Server sends a longer chain with more CA cer9ficates higher in the hierarchy – Both CAs trusted by Firefox SAPO Websecurity Team 25
- 36. How it works > Certificate chain of trust check • What can go wrong? SAPO Websecurity Team 26
- 37. How it works > Certificate chain of trust check • What can go wrong? • You do not trust what your browser trusts – Firefox ships with 76 CAs • Chunghwa Telecom Co., Ltd • Türkiye Bilimsel ve Teknolojik AraşUrma Kurumu -‐ TÜBİTAK – Are all of them secure and properly managed? SAPO Websecurity Team 26
- 38. How it works > Certificate chain of trust check • What can go wrong? • You do not trust what your browser trusts – Firefox ships with 76 CAs • Chunghwa Telecom Co., Ltd • Türkiye Bilimsel ve Teknolojik AraşUrma Kurumu -‐ TÜBİTAK – Are all of them secure and properly managed? – “I have not been able to find the current owner of this root. Both RSA and VeriSign have stated in email that they do not own this root.” said one of the maintainers of Mozilla CA list (early 2010) SAPO Websecurity Team 26
- 39. How it works > Certificate chain of trust check • What can go wrong? • You do not trust what your browser trusts – Recent request to add a CA to Firefox • “This is a request to add the CA root cerAficate for Honest Achmed's Used Cars and CerAficates.” • “Achmed's uncles all vouch for the fact that he's honest.” • “The purpose of this cerAficate is to allow Honest Achmed to sell bucketloads of other cerAficates and make a lot of money.” – It was not granted. This 9me. SAPO Websecurity Team 27
- 40. How it works > Certificate chain of trust check • How to mi9gate this problem? • Remove trust or delete CAs – they might come back aler solware updates – how do you evaluate if a CA can be trusted? – can you do this in your smartphone? SAPO Websecurity Team 28
- 41. How it works > Fetching content • At this point the browser trusts the site cer9ficate • No HTTP request was made yet! • First HTTP request is made only now GET / HTTP/1.1 Host: www.facebook.com SAPO Websecurity Team 29
- 42. How it works > Fetching content SAPO Websecurity Team 30
- 43. How it works > Redirecting from HTTP to HTTPS • Lets go back a lidle • Imagine you type hdp://www.facebook.com instead of hdps... • Hit enter! SAPO Websecurity Team 31
- 44. How it works > Redirecting from HTTP to HTTPS • Lets go back a lidle • Imagine you type hdp://www.facebook.com instead of hdps... • Hit enter! • Browser connects to www.facebook.com:80 SAPO Websecurity Team 31
- 45. How it works > Redirecting from HTTP to HTTPS SAPO Websecurity Team 32
- 46. How it works > Redirecting from HTTP to HTTPS SAPO Websecurity Team 33
- 47. How it works > Redirecting from HTTP to HTTPS SAPO Websecurity Team 34
- 48. How it works > Redirecting from HTTP to HTTPS • What can go wrong? SAPO Websecurity Team 35
- 49. How it works > Redirecting from HTTP to HTTPS • What can go wrong? • Moxie Marlinskipe and his sslstrip tool SAPO Websecurity Team 35
- 50. How it works > Redirecting from HTTP to HTTPS • What can go wrong? • Moxie Marlinskipe and his sslstrip tool SAPO Websecurity Team 35
- 51. How it works > Redirecting from HTTP to HTTPS • sslstrip func9oning – MiTM tool – maps HTTPS links to HTTP – maps redirects to HTTPS back to HTTP – maps HTTPS links to homograph-‐similar HTTPS links – can supply a lock favicon – logging! SAPO Websecurity Team 36
- 52. How it works > Redirecting from HTTP to HTTPS • sslstrip func9oning SAPO Websecurity Team 37
- 53. How it works > Redirecting from HTTP to HTTPS SAPO Websecurity Team 38
- 54. How it works > Redirecting from HTTP to HTTPS • You type hdp://www.facebook.com and get redirected to hdps://www.facebook.com GET / HTTP/1.1 Host: www.facebook.com HTTP/1.1 302 Found Location: https://www.facebook.com/ • These requests are not protected with SSL! SAPO Websecurity Team 39
- 55. How it works > Redirecting from HTTP to HTTPS • How to mi9gate this problem? SAPO Websecurity Team 40
- 56. How it works > Redirecting from HTTP to HTTPS • How to mi9gate this problem? • Make site available only in HTTPS – Does not work: most users type HTTP and redirects are dangerous SAPO Websecurity Team 40
- 57. How it works > Redirecting from HTTP to HTTPS • How to mi9gate this problem? • Make site available only in HTTPS – Does not work: most users type HTTP and redirects are dangerous • Use HSTS: HTTP Strict Transport Security – Formerly STS – Server defined policy that browsers must honor – Server sends HTTP header with policy SAPO Websecurity Team 40
- 58. How it works > Redirecting from HTTP to HTTPS Strict-Transport-Security: max-age=15768000;includeSubdomains • This header says two things: – “Browser, convert all requests to my domain to HTTPS” – “Browser, if there is any security issue with the connec9on do not allow progress” • Consequences: – the user types hdp://www.facebook.com and the browser requests hdps://www.facebook.com – any HTTP link in the response turns to HTTPS SAPO Websecurity Team 41
- 59. How it works > Redirecting from HTTP to HTTPS • S9ll, there is a problem: SAPO Websecurity Team 42
- 60. How it works > Redirecting from HTTP to HTTPS • S9ll, there is a problem: • We have never visited the site or policy expired – browser does not know the site HSTS policy – if the user types hdp://www.facebook.com the request is done using HTTP – TOFU: Trust On First Use • Recommenda9ons – first visit using a safe wired network – manually instruct the browser to use HSTS SAPO Websecurity Team 42
- 61. How it works > Redirecting from HTTP to HTTPS SAPO Websecurity Team 43
- 62. How it works > Redirecting from HTTP to HTTPS • Server support: all, just send the header • Browser support – Chrome 4.0.211.0 (with preloaded domain list) – Firefox 4 • Plugins – Safari SSL Everywhere – Firefox EFF HTTPS Everywhere – Firefox ForceTLS (simple list edi9ng) SAPO Websecurity Team 43
- 63. How it works > Redirecting from HTTP to HTTPS SAPO Websecurity Team 44
- 64. How it works > Redirecting from HTTP to HTTPS SAPO Websecurity Team 44
- 65. How it works > Redirecting from HTTP to HTTPS SAPO Websecurity Team 45
- 66. How it works > Redirecting from HTTP to HTTPS SAPO Websecurity Team 45
- 67. How it works > Full HTTPS browsing • At this point we have all the contents of the site served over HTTPS. • How can we be sure? • No9ce the green hdps text SAPO Websecurity Team 46
- 68. How it works > Mixed content browsing • How about this situa9on? • No9ce the red strikethrough hdps text SAPO Websecurity Team 47
- 69. How it works > Mixed content browsing • Chrome console output: SAPO Websecurity Team 48
- 70. How it works > Mixed content browsing • What is the problem? SAPO Websecurity Team 49
- 71. How it works > Mixed content browsing • What is the problem? • Sensi9ve informa9on can be captured – images: your last night weird photos – javascript: can be replaced with malicious code – cookies: sent in every request! – full browsing informa9on • Browser warnings – can affect site reputa9on – most users ignore this SAPO Websecurity Team 49
- 72. How it works > Mixed content browsing SAPO Websecurity Team 50
- 73. How it works > Mixed content browsing SAPO Websecurity Team 50
- 74. How it works > Mixed content browsing • How to mi9gate this problem? SAPO Websecurity Team 51
- 75. How it works > Mixed content browsing • How to mi9gate this problem? • HSTS – you have to specify all domains used by the site – some links might not work over HTTPS – not a solu9on for all sites SAPO Websecurity Team 51
- 76. How it works > Mixed content browsing • How to mi9gate this problem? • HSTS – you have to specify all domains used by the site – some links might not work over HTTPS – not a solu9on for all sites • Use only HTTPS links :) – use a proxy: make your server fetch the HTTP content and serve it over HTTPS – do not forget the favicon SAPO Websecurity Team 51
- 77. How it works > Mixed content browsing • How to minimize this problem? SAPO Websecurity Team 52
- 78. How it works > Mixed content browsing • How to minimize this problem? • Secure Cookies – the server can set the secure flag for the cookie – a secure cookie is only sent over HTTPS – beware: this does not prevent the mixed content warning, it ONLY prevents cookies from being sent over HTTP SAPO Websecurity Team 52
- 79. Recommendations • A few more recommenda9ons SAPO Websecurity Team 53
- 80. Recommendations • A few more recommenda9ons • Make a bookmark with the HTTPS link for the site (specially homebanking sites) – avoids requests using HTTP – avoids adacks caused by typos • Use a plugin that warns you if the cer9ficate has changed – Perspec9ves (www.networknotary.org) – Cer9ficate Patrol SAPO Websecurity Team 53
- 81. Conclusions • Conclusions – SSL 3.0 and TLS 1.0+ are the way to go – Use HSTS and manually add your important sites – Update your browser olen or automa9cally – Do not visit sites which the first page is HTTP using public wireless networks – Do not create sites with mixed HTTP(S) content – If your site is HTTPS only, use secure cookies SAPO Websecurity Team 54
- 82. Questions Any ques9ons? 9ago.mendo@telecom.pt SAPO Websecurity Team 55