Executive summary

There is a directory traversal vulnerability (CVE-2025-8562) in the WordPress plugin Custom Query Shortcode affecting versions ≤ 0.4.0. An authenticated user with Contributor privileges (or higher) can manipulate the plugin’s lens parameter to traverse directories on the server and potentially read files outside the intended plugin directory. The issue has been fixed in version 0.5.0.

As a Hong Kong-based security practitioner, I explain what this vulnerability means, how attackers may attempt to abuse it, how to detect attempts or confirmed exploitation, immediate mitigations, and longer-term hardening steps. This advisory avoids publishing weaponizable exploit code while providing operational detail to make fast, informed decisions.

What is the vulnerability?

• Affected plugin: Custom Query Shortcode
• Vulnerable versions: ≤ 0.4.0
• Fixed in: 0.5.0
• Vulnerability type: Directory Traversal (local file disclosure / information leakage)
• CVE: CVE-2025-8562
• Required privilege to exploit: Contributor (authenticated)
• Reported by: Muhammad Yudha (credited)

In short: the plugin accepts a lens parameter (used in its shortcode) which is not properly validated or sanitised. By supplying crafted values for that parameter, an authenticated Contributor can cause the plugin to reference files outside the intended path — enabling enumeration or reading of files that the web server user can access.

Why directory traversal matters

Directory traversal vulnerabilities allow attackers to request files the application was never intended to serve (configuration files, backups, theme/plugin source, private keys if readable by the web server). Direct impacts are information disclosure:

• Access to secrets, API keys, database credentials stored in files.
• Insight into site structure and installed software that aids follow-on attacks.
• Exposure of private uploads or backups containing PII or credentials.

Although directory traversal often only provides read access, the disclosed information commonly leads to further compromise (for example, leaked DB credentials used to pivot).

Who is at risk?

Any WordPress site running Custom Query Shortcode at version 0.4.0 or earlier is vulnerable if:

• The plugin is active, and
• The site allows user accounts with the Contributor role (or higher), or an attacker has obtained Contributor-level access by other means.

Many sites permit self-registration or use third-party plugins that assign roles; an attacker who can register as Contributor — or compromise such an account — can exploit this vulnerability.

How an attacker can abuse this (high level)

1. Attacker obtains an account with Contributor privileges (registering if allowed, credential stuffing, social engineering, or by compromising another account).
2. Attacker submits a page or post containing the vulnerable shortcode and supplies a crafted lens parameter with directory traversal sequences (e.g. ../ and encoded variants).
3. The plugin resolves a file path using the user-supplied value without sufficient sanitisation.
4. The server returns file contents or errors that leak path information, enabling enumeration and exfiltration of readable files.

No exploit strings are published here; the goal is to clarify the attack flow for defenders.

Attack prerequisites and limitations

• Privilege requirement: Contributor or higher (authenticated). Anonymous attackers cannot directly exploit this unless the site is misconfigured to accept anonymous shortcode input.
• File reads are limited to files readable by the web server user (e.g. www-data); OS-protected files may be safe.
• This vulnerability does not automatically grant remote code execution, but reading sensitive files (like wp-config.php) can greatly increase attacker options.

Immediate actions (what you should do now)

If you manage a WordPress site with this plugin, follow these steps immediately:

1. Verify plugin installation and version:
   • Dashboard: Plugins → Installed Plugins → locate “Custom Query Shortcode”.
   • WP-CLI: wp plugin list | grep custom-query-shortcode
2. Update the plugin to 0.5.0 or later as soon as possible:
   • Dashboard: Plugins → Update
   • WP-CLI: wp plugin update custom-query-shortcode
3. If you cannot update immediately:
   • Deactivate the plugin until you can update.
   • If the plugin is required and cannot be updated safely, remove it until a safe upgrade is available.
4. Review and limit user roles:
   • Review accounts with Contributor or higher privileges.
   • Remove or downgrade unexpected accounts and enforce strong passwords.
   • Enable two-factor authentication for authors and higher where possible.
5. Scan for indicators of compromise:
   • Check access logs for requests that include lens= or suspicious POST data.
   • Search for unusual file reads or downloads (grep for wp-config.php reads, backup file access).
   • Run a full site malware scan and compare core/plugin/theme files to clean copies.
6. Rotate secrets if you suspect leakage:
   • Change database credentials if wp-config.php may have been accessed.
   • Rotate API keys, tokens, SMTP and payment gateway credentials if exposed.

How to detect exploitation attempts

Inspect web server access logs, application logs and WordPress activity logs for suspicious patterns.

Search examples (run as a user with log access):

grep -i "lens=" /var/log/apache2/*access* /var/log/nginx/*access* | less
zgrep -i "lens=" /var/log/apache2/*.gz
    

WordPress checks:

wp post list --post_type=post,page --format=ids | xargs -n1 -I% wp post get % --field=post_content | grep -i "lens=" -n
    

Audit patterns to watch for:

• Percent-encoded traversal sequences: %2e%2e%2f, %2e%2e/, etc.
• Requests referencing filenames outside expected plugin directories or returning 200 with file contents.
• Unexpected 200 responses where 404/403 would be expected.

Examples to look for in logs:

• GET /some-post?lens=../../wp-config.php
• POST /wp-admin/admin-post.php body includes lens=../../

Monitoring for any requests containing the lens parameter with dot-dot patterns is a quick, practical detection rule.

WAF and virtual patching guidance

If you operate a Web Application Firewall (WAF) or have access to an application layer filtering mechanism, deploy a targeted rule to reduce risk until the plugin is patched:

Recommended detection and block criteria (conceptual):

• Block requests where any parameter named lens contains:
  • Unescaped directory traversal sequences such as ../, ..\ or their URL-encoded equivalents (%2e%2e%2f, %2e%2e%5c, etc.).
  • Path separators combined with .. patterns (after URL decoding).
• Block attempts to access well-known sensitive filenames via parameters (e.g. wp-config.php, .env, id_rsa, .git/).

Example pseudo-regex (adapt before use in your WAF / proxy):

# After URL decoding, detect if 'lens' contains traversal:
(^|[&?])lens=.*(\.\./|\.\.\\|%2e%2e%2f|%2e%2e%5c)
    

Important: test rules in detection mode first to avoid false positives. Some legitimate applications may use dot characters for valid reasons.

Hardening the site beyond the immediate fix

After applying the vendor patch or deactivating the plugin, implement these recommended controls:

1. Principle of least privilege:
   • Only grant Contributor-or-higher roles to those who actually need them.
   • Consider custom roles scoped narrowly for content contributors.
2. Harden PHP and the server:
   • Enable open_basedir restrictions to limit filesystem access to WordPress directories.
   • Disable dangerous directives you don’t need (e.g. allow_url_include), and prevent execution of PHP in upload directories.
3. File and directory permissions:
   • Set directories to 755 and files to 644 where appropriate.
   • Ensure sensitive files are readable only by the webserver user where practical.
4. Disable directory listing in web server configuration.
5. Remove or replace unused plugins and themes; delete inactive plugins you do not use.
6. Monitor integrity:
   • Use file integrity monitoring to detect unexpected changes.
   • Schedule regular automated scans for malware and unexpected files.
7. Registration policy:
   • Disable open registration if not needed (Settings → General → Membership).
   • If registration is required, add moderation or vetting.
8. Authentication and authorization:
   • Require email verification and moderate new accounts.
   • Enable two-factor authentication for roles that can publish or upload files (Author, Editor, Administrator).

For developers: secure handling of inputs and shortcodes

Developers should adopt these controls to avoid similar issues:

• Never use user-supplied input directly to build filesystem paths. Resolve to a canonical base directory and validate the result (use realpath() and confirm the prefix matches).
• Sanitise and normalise all parameters: URL-decode before validation, reject values containing dot-dot segments, absolute path tokens, or null bytes.
• Avoid dynamic includes based solely on user input.
• Use capability checks before any file operations triggered by user input.
• Keep dependencies up to date and review code paths that handle file I/O.

If you believe your site was breached

1. Isolate:
   • If you see clear signs of compromise, consider taking the site offline or enabling maintenance mode to limit further damage.
2. Preserve logs:
   • Collect and back up access, error, and application logs for forensic review.
3. Change credentials:
   • Reset all WordPress admin/editor accounts and database credentials if leakage is suspected.
   • Revoke API keys that may have been exposed.
4. Clean and restore:
   • Restore from a clean backup taken before the compromise if available.
   • If restore is not possible, replace core, theme and plugin files from known clean sources and remove unknown files.
5. Post-mortem:
   • Identify how the attacker gained access (vulnerability, stolen credential, etc.) and remediate root causes.
6. Notify stakeholders:
   • If customer data may have been exposed, follow legal and contractual disclosure obligations.

Practical detection recipes and commands

Safe, non-destructive commands to check for evidence of exploitation (run on your web server as a user with log access):

# Search access logs for lens parameter usage
grep -i "lens=" /var/log/apache2/*access* /var/log/nginx/*access* | less
zgrep -i "lens=" /var/log/apache2/*.gz

# Search posts/pages for suspicious shortcodes (WP-CLI)
wp post list --post_type=post,page --format=ids | xargs -n1 -I% wp post get % --field=post_content | grep -i "lens=" -n

# Find new or modified files in the webroot (last 30 days)
find /var/www/html -type f -mtime -30 -ls

# Look for reads of wp-config.php in logs
grep -i "wp-config.php" /var/log/apache2/*access* /var/log/nginx/*access*
    

Adjust paths to match your environment.

Long-term risk reduction: policies and process

To reduce future exposure, adopt these practises:

• Inventory and exposure management: maintain a current inventory of plugins/themes and track versions; subscribe to security advisories for high-risk components.
• Scheduled maintenance: automate safe plugin updates where possible and test updates in staging before production.
• Access governance: review user roles regularly and remove stale accounts; consider just-in-time access for contributors.
• Secure development lifecycle: run SAST, peer code reviews and harden third-party integrations.

Frequently asked questions

Q: If my site allows user registration but assigns Subscriber by default, am I still at risk?

A: The vulnerability requires Contributor privileges. If registrations result in Subscriber or another low-privilege role, direct risk is lower. However, account elevation via another plugin flaw or social engineering remains possible — monitor registration and role assignments.

Q: Does directory traversal mean the attacker can run commands on my server?

A: Not necessarily. Directory traversal primarily allows reading files accessible to the web server. But the obtained information (DB credentials, backups, keys) can be used for privilege escalation or remote code execution.

Q: I already updated to 0.5.0. Do I still need a WAF?

A: Yes. Patching is essential, but network/application filtering provides additional protection against automated attacks and zero-day exploits while you maintain patch discipline. Defence-in-depth remains best practice.

Closing notes

Directory traversal issues like this one are common and have a predictable exploitation pattern. Practical steps:

1. Update the plugin to 0.5.0 immediately (or deactivate/remove it until patched).
2. Audit Contributor and higher-privileged accounts and tighten user provisioning.
3. Monitor logs for suspicious lens usage and unexpected file reads.
4. Apply WAF or filtering rules to block traversal attempts until the plugin is patched.
5. Harden server configuration (open_basedir, permissions, directory listing) and follow secure development practices.

If you need assistance assessing exposure or implementing mitigations, engage a trusted security professional or your hosting provider to perform a site review and assist with incident response.

Stay vigilant — treat plugin updates and account governance as first-class elements of your site security programme.