URLs appended with /%&evalbase64_decode_SERVERHTTP_EXECCODE. &%/

Recently all of the internal links in my blog have broken. Every link has /%&evalbase64_decode_SERVERHTTP_EXECCODE.+&%/ tacked onto the end. If I request a page like so: https://www.studiy.tv/?p=195

I end up with a URL that looks like this:

https://www.studiy.tv/2010/02/01/tracking-an-8-piece-drum-kit-for-51-surround/%&evalbase64_decode_SERVERHTTP_EXECCODE.+&%/

I haven’t made any code changes recently and I can’t upgrade to the most recent version of WordPress because MySQL hasn’t been updated yet at my hosting company.

Anyone have any ideas?