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An explanation of webserver logs that contain requests such as "\x16\x03\x01"

Recently I have started coming across somewhat unusual entries in the access and error logs for a few of the Apache web servers that I am responsible for maintaining. The entries look like this: - - [03/Nov/2015:13:56:23 -0500] "\x16\x03\x02\x01o\x01" 400 226 "-" "-"

Here is another example: - - [03/Nov/2015:23:48:54 -0500] "\x16\x03\x01" 400 226 "-" "-"

These errors will be generated on a website configured to use SSL - and in fact, error messages similar to these can be generated by misconfiguring SSL for your website. This error message, for instance, can indicate an attempt to access Apache through SSL while the OpenSSL engine is either disabled or misconfigured:

Invalid method in request \x80g\x01\x03

Connections that generate that error would not be successful. This post, however, assumes that your website is working normally when used normally. So what gives?

The error indicates an attempt to scan OpenSSL for the SSLv3 POODLE vulnerability. No need to panic - getting scanned is an everyday occurrence for web server administrators, and hopefully your server is already long since patched for POODLE and disabled SSLv3 connections entirely. Furthermore, many of the servers scanning the internet making these connections are researchers - the example I provided above referencing the IP address is one such example, and belongs to a group called "The Shadowserver Foundation" that reviews the internet for vulnerabilities and publishes trends in their findings. 

Still, even the connections made by researchers are done without the consent of those being scanned - and some admins might not like that. Furthermore, there are plenty of people who are doing this sort of scanning that don't have the best interests of the internet community at heart. Blacklisting IP addresses that perform these sorts of connections is possible - but I recommend avoiding the use of blacklisting based on generalized formatting of OpenSSL errors as such a policy runs the risk of banning users or even yourself during troubleshooting or maintenance.