An issue was discovered in Tiny Tiny RSS (aka tt-rss) before 2020-09-16. It does not validate all URLs before requesting them.
https://git.tt-rss.org/fox/tt-rss/commit/c3d14e1fa54c7dade7b1b7955575e2991396d7ef
https://community.tt-rss.org/t/heads-up-several-vulnerabilities-fixed/3799
http://packetstormsecurity.com/files/161606/TinyTinyRSS-Remote-Code-Execution.html