Urgent: CVE-2025-11993 — PHP Object Injection in WooCommerce Infinite Scroll (≤ 1.8) — What WordPress Site Owners Must Do Now

Author: Hong Kong Security Expert | Published: 2026-06-01

Executive summary

A critical vulnerability (CVE-2025-11993) affects the WooCommerce Infinite Scroll and Ajax Pagination plugin (versions ≤ 1.8). This is a PHP deserialization / object injection flaw exploitable by an authenticated user with Subscriber privileges. The reported CVSS is 8.8 (High). Successful exploitation can yield remote code execution, privilege escalation and full site takeover.

From a Hong Kong security practitioner’s perspective: treat any site running this plugin as at immediate risk. The guidance below explains the technical issue, how attackers abuse it, what to detect now, and concrete mitigation and recovery steps you can apply immediately.

What is the vulnerability?

• Identifier: CVE-2025-11993
• Affected software: WooCommerce Infinite Scroll and Ajax Pagination — versions ≤ 1.8
• Vulnerability class: Deserialization of untrusted data / PHP Object Injection
• Required privilege: Authenticated Subscriber
• CVSS (reported): 8.8 (High)
• Status at disclosure: No official patch available at time of writing

In short: the plugin accepts serialized PHP data from authenticated users and passes it to an unsafe unserialize() call (or otherwise deserializes untrusted input). An attacker with Subscriber access can craft serialized PHP objects that instantiate classes with dangerous magic methods (for example __wakeup(), __destruct()), or leverage gadget chains within WordPress, plugins or themes to trigger arbitrary actions including code execution.

Why this is dangerous

PHP serialized strings can instantiate objects of arbitrary classes. If those classes have magic methods performing file, database or system actions, an attacker can craft serialized objects to trigger unintended behaviour. Consequences commonly include:

• Remote code execution (RCE) and full site takeover
• Creation or modification of admin accounts
• Upload or activation of web shells and persistent backdoors
• Data exfiltration (user records, orders, tokens)
• Site defacement or inclusion in automated exploit campaigns

Because Subscriber access is sufficient, many sites that accept registrations or have customer accounts are at heightened risk.

How attackers typically exploit this class of vulnerability

1. Register many accounts (if registration is open) or gain Subscriber access via credential stuffing / social engineering.
2. Identify the vulnerable endpoint (often an AJAX endpoint, REST route, or plugin form) that accepts serialized data.
3. Craft serialized payloads targeting classes present in the environment whose magic methods perform sensitive actions.
4. Submit payloads via POST to the endpoint. If unserialize() is called without protections, PHP rebuilds the object and may invoke dangerous methods.
5. Achieve the malicious outcome (RCE, privilege escalation, file write, etc.).

Immediate detection: what to look for

If you suspect attempted exploitation or compromise, prioritise these checks:

• Web server logs: POST requests to admin-ajax.php or plugin-specific endpoints from authenticated user sessions.
• Search for serialized patterns in request bodies: look for O:\d+:, C: or unusually long serialized strings.
• New or mass-created Subscriber accounts (sequential emails or similar patterns).
• Unusual user activity: unexpected password resets, strange metadata on orders or usermeta changes.
• File changes in wp-content/uploads, wp-content/plugins, or core PHP files — unknown .php files are high risk.
• Modified cron jobs or unknown scheduled events in wp_options.
• Outbound connections from the host to suspicious domains (check hosting logs if available).

Quick grep examples (run only if you have shell access):

# Search plugin directory for unsafe uses of unserialize
grep -RIn "unserialize" wp-content/plugins/sb-woocommerce-infinite-scroll || true

# Check web server logs for serialized payload patterns
grep -IEn "O:[0-9]+:\"" /var/log/nginx/access.log* /var/log/apache2/access.log* || true

# Check for recent file modifications
find wp-content -type f -mtime -7 -print

Immediate mitigation steps (priority order)

1. Take an immediate snapshot / backup (files + database). Preserve an immutable copy for potential forensic work.
2. If safe, deactivate the vulnerable plugin immediately.
   • WP dashboard: Plugins → deactivate WooCommerce Infinite Scroll
   • WP-CLI: wp plugin deactivate sb-woocommerce-infinite-scroll
3. If you cannot deactivate due to production constraints, restrict access:
   • Disable public registration.
   • Limit site access to logged-in administrators or use maintenance mode.
4. Force re-authentication and reset credentials:
   • Reset admin credentials and other privileged accounts.
   • Force password resets for suspicious users and rotate API keys or third-party credentials.
5. Scan for indicators of compromise (web shells, unknown PHP files). If found, isolate the site and consider taking it offline for cleanup.
6. Deploy targeted WAF/virtual patch rules where possible to block exploitation signatures (examples below).
7. Monitor logs continuously for repeated patterns, new registrations, or scheduled event changes.

Recommended WAF mitigations (rules and examples)

If you cannot immediately remove or patch the plugin, virtual patching can reduce exposure. Below conceptual rules can be adapted to your environment — test on staging first to avoid false positives.

High-level strategy:

• Block POST bodies containing PHP serialized object patterns (e.g. O:\d+:).
• Block or challenge requests to plugin-specific AJAX or REST routes from recently created accounts.
• Enforce rate limits and challenge (CAPTCHA) for new accounts.

Example ModSecurity-style rules (conceptual):

# Block PHP serialized objects in POST body (prevent simple exploitation attempts)
SecRule REQUEST_METHOD "POST" "chain,phase:2,deny,log,status:403,id:100001,msg:'Block suspicious PHP serialized object in POST body'"
  SecRule REQUEST_BODY "(?:O:\s*\d+\s*:|C:\s*\d+\s*:)" "t:none,t:lowercase"

# Block suspicious admin-ajax calls that contain serialized objects
SecRule REQUEST_URI "(?:/wp-admin/admin-ajax\.php|/wp-json/)" "chain,phase:2,deny,log,status:403,id:100002,msg:'Block unserialize attempts in AJAX/REST request'"
  SecRule REQUEST_BODY "(?:O:\s*\d+\s*:|C:\s*\d+\s*:)" "t:none"

# Block access to a plugin-specific REST endpoint (replace with actual route if known)
SecRule REQUEST_URI "/wp-json/sb-infinite-scroll/.*" "phase:2,deny,log,status:403,id:100003,msg:'Block requests to infinite scroll endpoints'"

Notes:

• These rules can block legitimate traffic in rare cases; validate on staging first.
• Prefer challenge responses or rate-limiting over outright blocking when false positives risk breaking business flows.
• If you use a managed hosting provider, ask them to implement equivalent virtual patches or request a custom rule from their security team.

Short, defensive heuristics you can add to WordPress (fast deploy)

As an interim measure, add an mu-plugin that blocks suspicious POST payloads before plugins run. This is a stop-gap, not a fix.

 403));
    }
}, 1);
?>

Deployment notes:

• Place the file in wp-content/mu-plugins/ so it loads before standard plugins.
• This blocks POSTs containing serialized object indicators and reduces exploitation risk; remove or refine after an official patch is applied.

For plugin developers: how to fix this class of bug

1. Never call unserialize() on untrusted data. Use json_decode() for structured client input.
2. If unserialize() is unavoidable, use the allowed_classes option (PHP 7+):

   $data = @unserialize($raw, ['allowed_classes' => false]); // disallow objects entirely
   if ($data === false && $raw !== serialize(false)) {
       // handle parse error
   }
   

3. Validate and sanitize input prior to deserialization; enforce expected types and ranges.
4. Require capability checks and nonces on AJAX/REST endpoints:

   check_ajax_referer('your_action_nonce', 'security');
   if (! current_user_can('some_capability')) {
       wp_send_json_error('Insufficient privileges', 403);
   }
   

5. Avoid persisting client-supplied serialized PHP state; use server-side storage mechanisms (options, transients, usermeta).
6. Include unit tests that attempt to deserialize malicious payloads to validate safe behavior.

Detection and recovery checklist (step-by-step)

1. Snapshot and isolate:
   • Take full file and database backups immediately and store off-server.
   • Put the site into maintenance or offline mode if possible.
2. Identify scope:
   • Review webserver and WordPress logs for serialized payloads.
   • List recently modified files: find . -type f -mtime -30 -print
   • Look for new admin users or role escalations.
3. Contain:
   • Deactivate the vulnerable plugin.
   • Disable public registration and remove suspicious subscribers.
   • Rotate all credentials (admin, FTP, hosting control panel, DB).
4. Clean:
   • Remove unknown PHP files only after careful verification.
   • Replace WordPress core files from a clean official source.
   • Reinstall plugins and themes from trusted sources.
   • If persistent backdoors exist, restore from a verified clean backup.
5. Reassess:
   • Run malware scans and file integrity checks.
   • Compare files against known-good copies and review scheduled tasks.
6. Post-incident:
   • Rotate external keys and secrets.
   • Review hosting logs for lateral movement.
   • Implement a patch management and monitoring strategy.

Hardening checklist (long-term prevention)

• Enforce least privilege for user accounts — do not grant customers administrative access.
• Use strong, unique passwords and enforce strong password policies.
• Enable two-factor authentication for administrative accounts.
• Keep WordPress core, themes and plugins up-to-date; monitor vendor advisories.
• Limit plugin usage to well-maintained extensions and remove unused plugins/themes.
• Enable file-write protections where possible (secure wp-config.php, define('DISALLOW_FILE_EDIT', true);).
• Use a WAF or hosting-level filtering with virtual patching capabilities and maintain custom rules for high-risk endpoints.
• Monitor logs for anomalies and configure alerts for suspicious activity.
• Regularly back up and test restores.

Example: confirming plugin vulnerability on your site

Use WP-CLI to check installed plugin versions:

# List plugin and version
wp plugin list --format=table | grep sb-woocommerce-infinite-scroll -i

If the version returned is 1.8 or lower, treat it as vulnerable. Search the plugin code for unserialize usage:

grep -RIn "unserialize" wp-content/plugins/sb-woocommerce-infinite-scroll || true

Unvalidated unserialize() calls are strong evidence of the vulnerability.

What to do if you rely on a hosting provider or agency

• Inform your host immediately and ask them to block exploit traffic to your site.
• Request a virtual patch or custom WAF rule to block serialized object payload signatures.
• Work with your developer or agency to remove or disable the plugin until a patch is available.
• If you manage multiple sites on the same account, treat them all as potentially impacted and investigate accordingly.

Incident response timeline (recommended)

• Hour 0: Back up site, deactivate plugin, restrict registrations, change admin passwords.
• Hour 1–6: Put a virtual patch in place (block serialized object patterns) or deploy the MU-plugin snippet above.
• Day 1: Run full malware scan and begin forensic checklist.
• Day 1–3: Sweep for persistence (unknown scheduled events, mu-plugins, modified core files).
• Day 3–7: Clean or restore from a clean backup; re-enable services with monitoring.
• Week 1+: Harden per checklist and continue monitoring for reattempts.

Why you should not rely only on a patch

Patches are necessary but not sufficient. Sites often remain unpatched due to upgrade workflows, staging/production lag, or missed notifications. Virtual patching, hardening and continuous monitoring provide defence in depth. Exploit chains can involve multiple components, so a single plugin patch may not eliminate risk entirely.

If you need assistance

If you require immediate help: contact your hosting provider, engage a trusted security consultant or an incident response team. Prioritise containment (disconnect from the network where appropriate), preserve forensic evidence (backups, logs) and coordinate credential rotation and cleanup with experienced responders.

Final recommendations (quick checklist)

• If you run WooCommerce Infinite Scroll ≤ 1.8: assume risk and act now.
• Deactivate the plugin if possible.
• If you cannot deactivate: deploy the stop-serialized-objects mu-plugin or implement WAF rules to block serialized object payloads.
• Force password changes for privileged accounts and review user accounts for suspicious activity.
• Back up your site immediately and begin forensic checks.
• Work with your host or a trusted security specialist to implement virtual patching and conduct a thorough investigation if compromise is suspected.

References and further reading

• Official CVE listing: CVE-2025-11993
• WordPress Developer Resources: AJAX security, nonces, users and capabilities
• PHP Manual: unserialize() options (allowed_classes)
• OWASP: Deserialization and Injection attack guidance

Published by a Hong Kong security practitioner — concise, practical steps for operators and developers to reduce immediate risk and recover safely.