SHIRASAGI prior to v1.19.1 processes URLs in HTTP requests improperly, resulting in a path traversal vulnerability. If this vulnerability is exploited, arbitrary files on the server may be retrieved when processing crafted HTTP requests.
https://jvn.jp/en/jp/JVN58721679/
https://github.com/shirasagi/shirasagi/commit/5ac4685d7e4330f949f13219069107fc5d768934