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# How we manage the TLS protocol CRIME vulnerability
> CRIME ("Compression Ratio Info-leak Made Easy") is a security exploit against
secret web cookies over connections using the HTTPS and SPDY protocols that also
use data compression.[1][2] When used to recover the content of secret
authentication cookies, it allows an attacker to perform session hijacking on an
authenticated web session, allowing the launching of further attacks.
([CRIME](https://en.wikipedia.org/w/index.php?title=CRIME&oldid=692423806))
### Description
The TLS Protocol CRIME Vulnerability affects compression over HTTPS therefore
it warns against using SSL Compression, take gzip for example, or SPDY which
optionally uses compression as well.
GitLab support both gzip and SPDY and manages the CRIME vulnerability by
deactivating gzip when https is enabled and not activating the compression
feature on SDPY.
Take a look at our configuration file for NGINX if you'd like to explore how the
conditions are setup for gzip deactivation on this link:
[GitLab NGINX File](https://gitlab.com/gitlab-org/omnibus-gitlab/blob/master/files/gitlab-cookbooks/gitlab/templates/default/nginx-gitlab-http.conf.erb).
For SPDY you can also watch how its implmented on NGINX at [GitLab NGINX File](https://gitlab.com/gitlab-org/omnibus-gitlab/blob/master/files/gitlab-cookbooks/gitlab/templates/default/nginx-gitlab-http.conf.erb)
but take into consideration the NGINX documentation on its default state here:
[Module ngx_http_spdy_module](http://nginx.org/en/docs/http/ngx_http_spdy_module.html).
### Nessus
The Nessus scanner reports a possible CRIME vunerability for GitLab similar to the
following format:
Description
This remote service has one of two configurations that are known to be required for the CRIME attack:
SSL/TLS compression is enabled.
TLS advertises the SPDY protocol earlier than version 4.
...
Output
The following configuration indicates that the remote service may be vulnerable to the CRIME attack:
SPDY support earlier than version 4 is advertised.
*[This](http://www.tenable.com/plugins/index.php?view=single&id=62565) is a complete description from Nessus.*
From the report above its important to note that Nessus is only checkng if TLS
advertises the SPDY protocol earlier than version 4, it does not perform an
attack nor does it check if compression is enabled. With just this approach it
cannot tell that SPDY's compression is disabled and not subject to the CRIME
vulnerbility.
### Reference
* Nginx. "Module ngx_http_spdy_module", Fri. 18 Dec.
* Tenable Network Security, Inc. "Transport Layer Security (TLS) Protocol CRIME Vulnerability", Web. 15 Dec.
* Wikipedia contributors. "CRIME." Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 25 Nov. 2015. Web. 15 Dec. 2015.
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