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# How we manage the TLS protocol CRIME vulnerability
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2015-12-25 08:23:06 -05:00
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> CRIME ("Compression Ratio Info-leak Made Easy") is a security exploit against
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secret web cookies over connections using the HTTPS and SPDY protocols that also
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use data compression. When used to recover the content of secret
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authentication cookies, it allows an attacker to perform session hijacking on an
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authenticated web session, allowing the launching of further attacks.
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([CRIME](https://en.wikipedia.org/w/index.php?title=CRIME&oldid=692423806))
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### Description
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2015-12-25 08:23:06 -05:00
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The TLS Protocol CRIME Vulnerability affects compression over HTTPS, therefore
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it warns against using SSL Compression (for example gzip) or SPDY which
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optionally uses compression as well.
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2015-12-25 08:23:06 -05:00
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GitLab supports both gzip and [SPDY][ngx-spdy] and mitigates the CRIME
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vulnerability by deactivating gzip when HTTPS is enabled. You can see the
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sources of the files in question:
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2018-11-13 01:07:16 -05:00
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- [Source installation NGINX file][source-nginx]
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- [Omnibus installation NGINX file][omnibus-nginx]
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2015-12-25 08:23:06 -05:00
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Although SPDY is enabled in Omnibus installations, CRIME relies on compression
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(the 'C') and the default compression level in NGINX's SPDY module is 0
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(no compression).
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### Nessus
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The Nessus scanner, [reports a possible CRIME vulnerability][nessus] in GitLab
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similar to the following format:
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2015-12-25 08:23:06 -05:00
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```
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Description
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2015-12-25 08:23:06 -05:00
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This remote service has one of two configurations that are known to be required for the CRIME attack:
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SSL/TLS compression is enabled.
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TLS advertises the SPDY protocol earlier than version 4.
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2015-12-25 08:23:06 -05:00
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...
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2015-12-25 08:23:06 -05:00
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Output
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2015-12-25 08:23:06 -05:00
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The following configuration indicates that the remote service may be vulnerable to the CRIME attack:
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SPDY support earlier than version 4 is advertised.
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```
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2015-12-25 08:23:06 -05:00
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From the report above it is important to note that Nessus is only checking if
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TLS advertises the SPDY protocol earlier than version 4, it does not perform an
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attack nor does it check if compression is enabled. With just this approach, it
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cannot tell that SPDY's compression is disabled and not subject to the CRIME
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vulnerability.
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### References
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2018-11-13 01:07:16 -05:00
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- Nginx ["Module ngx_http_spdy_module"][ngx-spdy]
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- Tenable Network Security, Inc. ["Transport Layer Security (TLS) Protocol CRIME Vulnerability"][nessus]
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- Wikipedia contributors, ["CRIME"][wiki-crime] Wikipedia, The Free Encyclopedia
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2015-12-25 08:23:06 -05:00
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[source-nginx]: https://gitlab.com/gitlab-org/gitlab-ce/blob/master/lib/support/nginx/gitlab-ssl
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[omnibus-nginx]: https://gitlab.com/gitlab-org/omnibus-gitlab/blob/master/files/gitlab-cookbooks/gitlab/templates/default/nginx-gitlab-http.conf.erb
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[ngx-spdy]: http://nginx.org/en/docs/http/ngx_http_spdy_module.html
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[nessus]: https://www.tenable.com/plugins/index.php?view=single&id=62565
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[wiki-crime]: https://en.wikipedia.org/wiki/CRIME
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