Recently I’ve come across an issue with users being unable to connect to https://slate.adobe.com using WorxWeb on both iOS and Android. Connection seems to terminate instantly as you enter the URL.
Digging further into this problem came up with some interesting results.
Doing a dig on slate.adobe.com returns a number of A records
; <<>> DiG 9.8.3-P1 <<>> slate.adobe.com ;; global options: +cmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 39445 ;; flags: qr rd ra; QUERY: 1, ANSWER: 9, AUTHORITY: 0, ADDITIONAL: 0 ;; QUESTION SECTION: ;slate.adobe.com. IN A ;; ANSWER SECTION: slate.adobe.com. 0 IN CNAME slate.adobestandout.com. slate.adobestandout.com. 60 IN A 126.96.36.199 slate.adobestandout.com. 60 IN A 188.8.131.52 slate.adobestandout.com. 60 IN A 184.108.40.206 slate.adobestandout.com. 60 IN A 220.127.116.11 slate.adobestandout.com. 60 IN A 18.104.22.168 slate.adobestandout.com. 60 IN A 22.214.171.124 slate.adobestandout.com. 60 IN A 126.96.36.199 slate.adobestandout.com. 60 IN A 188.8.131.52
The first record of the answer will change randomly, this seems to be a type of load balancing implemented by adobe.
An SSL scan on slate.adobe.com https://www.ssllabs.com/ssltest/analyze.html?d=slate.adobe.com&s=184.108.40.206 reveals "This site works only in browsers with SNI support."
Now we are using SecureBrowse for WorxWeb as a preferred VPN method.
SecureBrowse causes the netscaler to acts like a reverse proxy for the said traffic with the device traffic terminating on the netscaler and netscaler establishing a new SSL tunnel in order to fetch the requested traffic.
Due to this we can run a traffic capture on the netscaler in order to capture the SSL handshake (if we were to use Full Tunnel for VPN it would be a bit trickier as we would have to decrypt the traffic in order to see the handshake between the device and the target website).
Looking the SSL handshake traffic capture between netscaler and slate.adobe.com we can see that SSL handshake is failing.
However looking at the Client Hello we can see that the protocol being offered by the client and ciphers are actually supported by slate.adobe.com according to the SSL scan.
Secure Sockets Layer TLSv1 Record Layer: Handshake Protocol: Client Hello Content Type: Handshake (22) Version: TLS 1.0 (0x0301) Length: 139 Handshake Protocol: Client Hello Handshake Type: Client Hello (1) Length: 135 Version: TLS 1.0 (0x0301) Random GMT Unix Time: Jan 14, 2016 11:46:26.000000000 NZDT Random Bytes: a562d85be83e6aa825121dd960976ec17353b5f7b433f284... Session ID Length: 32 Session ID: 040a5645c6c2ea8abcaedd6b35b8013efc6a788b4134d6b3... Cipher Suites Length: 64 Cipher Suites (32 suites) Cipher Suite: TLS_RSA_WITH_RC4_128_MD5 (0x0004) Cipher Suite: TLS_RSA_WITH_RC4_128_SHA (0x0005) Cipher Suite: TLS_RSA_EXPORT_WITH_RC4_40_MD5 (0x0003) Cipher Suite: TLS_RSA_WITH_DES_CBC_SHA (0x0009) Cipher Suite: TLS_RSA_WITH_3DES_EDE_CBC_SHA (0x000a) Cipher Suite: TLS_RSA_EXPORT_WITH_DES40_CBC_SHA (0x0008) Cipher Suite: TLS_RSA_EXPORT1024_WITH_RC4_56_SHA (0x0064) Cipher Suite: TLS_RSA_EXPORT1024_WITH_RC4_56_MD5 (0x0060) Cipher Suite: TLS_RSA_EXPORT1024_WITH_RC2_CBC_56_MD5 (0x0061) Cipher Suite: TLS_RSA_EXPORT_WITH_RC2_CBC_40_MD5 (0x0006) Cipher Suite: TLS_DHE_DSS_WITH_RC4_128_SHA (0x0066) Cipher Suite: TLS_DHE_DSS_EXPORT1024_WITH_RC4_56_SHA (0x0065) Cipher Suite: TLS_DHE_DSS_EXPORT1024_WITH_DES_CBC_SHA (0x0063) Cipher Suite: TLS_RSA_WITH_AES_128_CBC_SHA (0x002f) Cipher Suite: TLS_RSA_WITH_AES_256_CBC_SHA (0x0035) Cipher Suite: TLS_DHE_RSA_WITH_DES_CBC_SHA (0x0015) Cipher Suite: TLS_DHE_RSA_WITH_3DES_EDE_CBC_SHA (0x0016) Cipher Suite: TLS_DHE_RSA_EXPORT_WITH_DES40_CBC_SHA (0x0014) Cipher Suite: TLS_DHE_RSA_WITH_AES_128_CBC_SHA (0x0033) Cipher Suite: TLS_DHE_RSA_WITH_AES_256_CBC_SHA (0x0039) Cipher Suite: TLS_DHE_DSS_WITH_DES_CBC_SHA (0x0012) Cipher Suite: TLS_DHE_DSS_WITH_3DES_EDE_CBC_SHA (0x0013) Cipher Suite: TLS_DHE_DSS_EXPORT_WITH_DES40_CBC_SHA (0x0011) Cipher Suite: TLS_DHE_DSS_WITH_AES_128_CBC_SHA (0x0032) Cipher Suite: TLS_DHE_DSS_WITH_AES_256_CBC_SHA (0x0038) Cipher Suite: TLS_DH_anon_WITH_RC4_128_MD5 (0x0018) Cipher Suite: TLS_DH_anon_WITH_DES_CBC_SHA (0x001a) Cipher Suite: TLS_DH_anon_WITH_3DES_EDE_CBC_SHA (0x001b) Cipher Suite: TLS_DH_anon_EXPORT_WITH_RC4_40_MD5 (0x0017) Cipher Suite: TLS_DH_anon_EXPORT_WITH_DES40_CBC_SHA (0x0019) Cipher Suite: TLS_DH_anon_WITH_AES_128_CBC_SHA (0x0034) Cipher Suite: TLS_DH_anon_WITH_AES_256_CBC_SHA (0x003a) Compression Methods Length: 1 Compression Methods (1 method) Compression Method: null (0)
This was a bit puzzling to me until I’ve read more about SNI.
SNI is a method of hosting multiple certificates on the same web server IP & port.
SNI relies on the hostname to be provided in the client hello in order to be able to answer the SSL handshake.
You can read more about SNI here. https://en.wikipedia.org/wiki/Server_Name_Indication
I’ve ran wireshark on my machine while attempting to access the same site and I could see a few additional lines in the Client Hello, specifically:
Extension: server_name Type: server_name (0x0000) Length: 20 Server Name Indication extension Server Name list length: 18 Server Name Type: host_name (0) Server Name length: 15 Server Name: slate.adobe.com
Now it all makes sense, as we are not presenting the above in the Client Hello sent by the netscaler the web server in question has no idea which SSL certificate is being requested therefore closing the connection with ssl handshake error.
This can be replicated in OpenSSL
openssl s_client -connect slate.adobe.com:443
will return a handshake error
openssl s_client -servername slate.adobe.com -connect slate.adobe.com:443
will connect successfully
It does not seem like the Netscaler Gateway module has support for SNI therefore slate.adobe.com cannot be reached. I currently have a ticket open with Citrix in order to see if this is something that can be enabled or something that exists in other versions of the netscaler otherwise slate.adobe.com will not be accessible from WorxWeb.