Doesn't return 404 on nonexisting files

What happened?

If you have an index.php file in the website root, any request to nonexisting files will be executed by index.php and return 200. This will result in incorrect responses serving the actual website content on nonexisting paths with the incorrect status code (200) instead of 404.

If this is the intended behaviour, is it possible to disable it?

Build Type

Docker (Debian Trixie)

Worker Mode

No

Operating System

GNU/Linux

CPU Architecture

x86_64

PHP configuration

System 	Linux 2e987d8e2f6e 6.12.43+deb13-amd64 #1 SMP PREEMPT_DYNAMIC Debian 6.12.43-1 (2025-08-27) x86_64
Build Date 	Aug 28 2025 18:15:48
Build System 	Linux - Docker
Build Provider 	https://github.com/docker-library/php
Configure Command 	'./configure' '--build=x86_64-linux-gnu' '--with-config-file-path=/usr/local/etc/php' '--with-config-file-scan-dir=/usr/local/etc/php/conf.d' '--enable-option-checking=fatal' '--with-mhash' '--with-pic' '--enable-mbstring' '--enable-mysqlnd' '--with-password-argon2' '--with-sodium=shared' '--with-pdo-sqlite=/usr' '--with-sqlite3=/usr' '--with-curl' '--with-iconv' '--with-openssl' '--with-readline' '--with-zlib' '--enable-phpdbg' '--enable-phpdbg-readline' '--with-pear' '--with-libdir=lib/x86_64-linux-gnu' '--enable-embed' '--enable-zts' '--disable-zend-signals' 'build_alias=x86_64-linux-gnu' 'PHP_UNAME=Linux - Docker' 'PHP_BUILD_PROVIDER=https://github.com/docker-library/php'
Server API 	FrankenPHP
Virtual Directory Support 	enabled
Configuration File (php.ini) Path 	/usr/local/etc/php
Loaded Configuration File 	(none)
Scan this dir for additional .ini files 	/usr/local/etc/php/conf.d
Additional .ini files parsed 	/usr/local/etc/php/conf.d/docker-php-ext-opcache.ini, /usr/local/etc/php/conf.d/docker-php-ext-sodium.ini
PHP API 	20240924
PHP Extension 	20240924
Zend Extension 	420240924
Zend Extension Build 	API420240924,TS
PHP Extension Build 	API20240924,TS
PHP Integer Size 	64 bits
Debug Build 	no
Thread Safety 	enabled
Thread API 	POSIX Threads
Zend Signal Handling 	disabled
Zend Memory Manager 	enabled
Zend Multibyte Support 	provided by mbstring
Zend Max Execution Timers 	enabled
IPv6 Support 	enabled
DTrace Support 	disabled
Registered PHP Streams	https, ftps, compress.zlib, php, file, glob, data, http, ftp, phar
Registered Stream Socket Transports	tcp, udp, unix, udg, ssl, tls, tlsv1.0, tlsv1.1, tlsv1.2, tlsv1.3
Registered Stream Filters	zlib.*, convert.iconv.*, string.rot13, string.toupper, string.tolower, convert.*, consumed, dechunk

Relevant log output

For example, when the browser tries to request /favicon.ico that doesn't exist, index.php will be executed and return the main website content as HTML:

caddy-1  | {"level":"info","ts":1757529977.5878327,"logger":"http.log.access","msg":"handled request","request":{"remote_ip":"1.2.3.4","remote_port":"50513","client_ip":"1.2.3.4","proto":"HTTP/2.0","method":"GET","host":"example.com","uri":"/favicon.ico","headers":{"Sec-Fetch-Dest":["image"],"Sec-Fetch-Site":["same-origin"],"Cache-Control":["no-cache"],"Accept":["image/avif,image/jxl,image/webp,image/png,image/svg+xml,image/*;q=0.8,*/*;q=0.5"],"Pragma":["no-cache"],"User-Agent":["Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:144.0) Gecko/20100101 Firefox/144.0"],"Priority":["u=6"],"Accept-Encoding":["gzip, deflate, br, zstd"],"Sec-Fetch-Mode":["no-cors"],"Te":["trailers"],"Accept-Language":["sl,en-GB;q=0.8,en-US;q=0.5,en;q=0.3"],"Referer":["https://example.com/test"]},"tls":{"resumed":false,"version":772,"cipher_suite":4865,"proto":"h2","server_name":"example.com"}},"bytes_read":0,"user_id":"","duration":0.003590894,"size":80152,"status":200,"resp_headers":{"Server":["Caddy"],"Alt-Svc":["h3=\":443\"; ma=2592000"],"X-Powered-By":["PHP/8.4.12"],"Content-Type":["text/html; charset=UTF-8"]}}

The report names no source files, tests, or entry points. Reproduce the behavior with an index.php in the website root and a request such as /favicon.ico, then trace how FrankenPHP handles the missing file and determine whether the expected 404 behavior or a documented configuration option is needed.