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The Long, Hard and Possibly Foolish Path to SSL/TLS Security

by @ 10:57 pm
Filed under: internet,web — Tags: , , , , , ,

... or TLS 1.2 on Fedora Core 14/FC14 and other older Linux versions

With the chorus of secure browsing  getting louder and becoming more prevalent,  HTTPS migration is becoming inevitable. Going secure is a pretty major undertaking, fraught with numerous pitfalls. It starts with the source files that produce the html pages and it could get ugly if there's even one element in a page that is called over http rather than https, no green padlock in that case. The Protocol-relative URL (//) instead of the hard-coded http:// or https:// is quite helpful to that end. That's one of side of the equation. The other is the server itself.

I run my site on an older server with an old Fedora Core OS (FC14) and by extension an older version of web server software, Apache 2.2.17. Over the years I have updated a few components here and there and fixed and customized a bunch of others, especially after new vulnerabilities have popped up. Updating the server to the latest and greatest version would be a non-trivial task for me. The old hardware may not be sufficiently supportive, much of the OS customizations will be lost, migrating the data and config files will be a pain and there will be downtime as well. Yet FC14 cannot support the newer and safer SSL/TLS technologies considered acceptable by today's browsers.

At my day job, I have access to resources to overcome this problem by fronting the web server with other servers running newer technologies. For example a combination of HAProxy and Varnish provides excellent web acceleration, load balancing, and SSL termination without making any updates to the core web server. No such luck for a small time operator such as myself with limited resources, so what to do?

One approach would be to only upgrade parts of the OS and Apache (httpd program) that deal with encryption but there isn't much in terms of online resources dealing with this topic other than the customary advice to upgrade the OS. In the end this became a long process of trial and error but it was a successful endeavor with a good bit of leaning as a bonus. Here's how I did it.

Apache 2.2.17 running on Fedora Core 14 can be configured for SSL, however it can only provide support for up to TLS1.0, with older cipher suites and the weak RSA key exchange. I had already patched OpenSSL after the Heartbleed bug had become public but what I needed were newer version of libcrypto.so.1.0.0 and libssl.so.1.0.0 libraries used by mod_ssl.so, a module used by httpd to enable SSL.

I downloaded the source and built OpenSSL version 1.0.1u. Building applications from source code in Linux is usually a three-step process, configure, make, and make install. After 'make install' The new OpenSSL libraries were placed in an alternate directory, /usr/local/ssl, instead of overwriting their main system counterparts.

Next step was to incorporate the new libcrypto.so.1.0.0 and libssl.so.1.0.0 libraries into mod_ssl.so and my tool of choice for that was patchelf. I downloaded and built patchelf 0.9.

Before using patchelf I took one step which I am not sure if it were necessary in hindsight. That step was adding the location of these new libraries to a conf file under /etc/ld.so.conf.d and executing the ldconfig command to add this new location to the library cache /etc/ld.so.cache used by the linker.

Here's an example of a command I used to replace one of the libraries in mod_ssl.so, I did the same for the other:

./patchelf --replace-needed libcrypto.so.1.0.0 libcrypto.so.1.0.0 mod_ssl.so

Then I used the ldd command to make sure mod_ssl.so was now linking to these new libraries.

Following an httpd restart and checking one of the secure pages I had the encouraging green padlock on Chrome browser. Indeed the page was using TLS1.2 now with a strong encryption/cipher. Yet the key exchange was using the obsoleted RSA. The new OpenSSL libraries had certainly made an improvement to mod_ssl.so but the strong key exchange element was missing.

To overcome that issue I had to rebuild mod_ssl.so with a newer version of Apache source code. That was version 2.2.32. configure was done with the following parameters:

./configure --enable-mods-shared="ssl"  --with-ssl=/usr/local/ssl

And after make I found the new mod_ssl.so in one of the subdirectories of the source files. I skipped the make install step to avoid possible complications of the new version installing itself in the system. Interestingly the new mod_ssl.so was already linked to the new libcrypto.so.1.0.0 and libssl.so.1.0.0 libraries I had created in the previous step. I suppose adding that directory to the library cache had helped with that.

I placed mod_ssl.so in the folder to be loaded by /etc/httpd/conf.d/ssl.conf and restarted httpd. And it failed to start with a message about a missing symbol ap_map_http_request_error! Obviously mod_ssl.so couldn't call into this function of the older httpd (or some library) version.

To fix that error I edited the file modules/ssl/ssl_engine_io.c and replaced the line:

return ap_map_http_request_error(rv, HTTP_INTERNAL_SERVER_ERROR);

with

return HTTP_INTERNAL_SERVER_ERROR;

I admit, this is a blind alteration with possible adverse repercussions, so I don't vouch for it. Executing make once again yielded a new mod_ssl.so and this time httpd started just fine, this time with a strong key exchange added in. Testing the site with SSL Labs gave additional confirmation that SSL encryption was indeed working fine.

If wondering, I use Let's Encrypt for free SSL certificates. The recommended utility for obtaining certificates is certbot but that tool with its overly complex and finicky python virtual environment wouldn't work under FC14. The tool that worked beautifully was getssl. It's a simple and clean, yet powerful and flexible script written as one executable file in bash script. Kudos to the getssl team for creating this robust tool.

So there you have it for enabling modern SSL/TLS in an older environment, in this case FC14. The prevailing wisdom is to abandon the old OS and start off fresh with a newer platform. I don't disagree with that philosophy and I set out to do just that when I started on this journey. In the end, my way was possibly more difficult and more prone to pitfalls but ultimately it ended up being more satisfying and more instructive.

I haven't migrated the entire site to HTTPS yet, but you can click secure whoami to view and examine the first secure page.

 

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