[squid-users] SSL Bump missing facebook app traffic (resumed SSL sessions?)

Cohen-Rose, Adam Adam.Cohen-Rose at sky.uk
Mon May 9 10:05:43 UTC 2016

Hi there,

We¹re running squid with SSL bump as a transparent proxy in order to
control access to particular SSL sites.

We¹ve noticed an issue with access to facebook from within the facebook
app -- specifically it can get through the proxy even though it is *not*
listed as a domain to splice. Accessing the facebook site from a web
browser is blocked as expected.

Looking at packets in Wireshark, the app traffic that gets through seems
to use a different style of SSL handshake from the web traffic as follows:

App traffic:
> client hello
< server hello, change cipher spec
  - change cipher spec message: this session reuses previously negotiated
keys (session resumption)
< encrypted handshake message
> change cipher spec, encrypted handshake message, application data
> application data

Web traffic:
> client hello
< server hello
< certificate
< server key exchange
> client key exchange
> change cipher spec
> encryped handshake message
< new session ticket, change cipher spec, encrypted handshake message
> application data

I suspect this may be the same or a similar issue referred to in the
3.5.19 release changes (TLS: Fix SSL alert message and session resume
handling) -- would someone please confirm or deny?

And if we were to upgrade to 3.5.19, is the build on Centos 6 a relatively
easy one? We¹ve been using Eliezer Croitoru¹s builds so far, but I don¹t
think he¹s had time to make the latest build yet!

For reference, the relevant parts of our squid configuration are as

https_port {squid-ip}:443 cert=/path/to/cert key=/path/to/key
sslflags=NO_DEFAULT_CA intercept ssl-bump
acl to_teads_tv_ssl ssl::server_name .teads.tv
ssl_bump splice to_teads_tv_ssl

acl hello at_step SslBump1 SslBump2
ssl_bump peek hello
ssl_bump terminate all

Thank you for your help!


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