An issue was discovered in Tiny Tiny RSS (aka tt-rss) before 2020-09-16. imgproxy in plugins/af_proxy_http/init.php mishandles $_REQUEST["url"] in an error message.
https://git.tt-rss.org/fox/tt-rss/commit/c3d14e1fa54c7dade7b1b7955575e2991396d7ef
https://community.tt-rss.org/t/heads-up-several-vulnerabilities-fixed/3799