CVE-2025-58839 — PHP Object Injection in eDS Responsive Menu (<= 1.2): What WordPress Site Owners Must Do Now

By: Hong Kong Security Expert • 2025-09-05

Summary: CVE-2025-58839 affects the WordPress plugin “eDS Responsive Menu” (versions ≤ 1.2). It is a PHP Object Injection (POI) vulnerability that can be abused if a suitable gadget/POP chain exists. The plugin appears unmaintained and no official fix was available at the time of disclosure. Exploitation requires Administrator privileges on the affected site — which reduces anonymous remote risk but leaves real-world exposure when admin accounts are compromised.

Executive summary — what you need to know right now

• Vulnerability: PHP Object Injection in eDS Responsive Menu (≤ 1.2) — CVE-2025-58839.
• Prerequisites: Attacker must have Administrator privileges on the site to exploit the flaw.
• Severity: High-impact potential (RCE, data access, persistence) when combined with appropriate gadget chains; administrative requirement lowers immediate remote risk but does not remove it.
• Official fix: None published at time of disclosure; plugin appears abandoned.
• Immediate actions: Remove or replace the plugin where possible, lock down admin accounts, rotate credentials, scan for compromise, and apply mitigation controls (server rules, WAF/virtual patching) where available.

What is PHP Object Injection (POI) — plain language

POI happens when PHP unserializes attacker-controlled data. The PHP function unserialize() can instantiate objects described by the serialized string. If attacker-controlled serialized data leads to creation of objects whose magic methods or internal logic perform filesystem, execution, or DB operations, an attacker can chain those behaviors to escalate impact. This is often called a POP (Property-Oriented Programming) or gadget chain.

Key concepts:

• Serialized data: Strings representing arrays/objects used for storage or transport.
• Untrusted input: Any user-influenced data (POST, cookies, options, imports).
• Gadget chain: Existing classes/methods that, when instantiated with controlled properties, produce side effects (file write, eval, DB calls).

Because WordPress installations often include many plugin/theme classes, a single insecure unserialize() can be dangerous site-wide if a gadget chain exists.

Why this matters even though admin privileges are required

• Administrator accounts are frequent targets via phishing, credential stuffing, or reused passwords. Once compromised, this vulnerability becomes powerful.
• Compromised or malicious insiders with admin rights can persist, plant backdoors, or pivot to other parts of the server.
• Abandoned plugins without timely fixes mean the vulnerability window may remain open indefinitely.

The specifics: eDS Responsive Menu (≤ 1.2)

• Affected software: eDS Responsive Menu (WordPress plugin)
• Vulnerable versions: ≤ 1.2
• Vulnerability type: PHP Object Injection (OWASP: Injection)
• CVE: CVE-2025-58839
• Exploitation privileges: Administrator
• Fixed version: None available (as of writing)
• Researcher credit: Reported responsibly by an independent researcher

High-level exploitation overview (safe, non-actionable)

1. The plugin accepts data that is passed to unserialize() without safe restrictions.
2. An attacker with admin privileges crafts serialized payloads (e.g., via plugin settings, imported options, or POST data) that are stored or processed by the plugin.
3. On unserialization, objects of classes present in the codebase are created with attacker-controlled properties.
4. If those classes contain methods that cause side effects (file writes, command execution, DB changes), a gadget chain can be exploited to achieve high-impact results.
5. Consequences vary by site: from content tampering to full site takeover depending on available gadgets.

Because gadget chains depend on the exact set of classes loaded on a site, payloads are site-specific — complicating detection and increasing the need for conservative mitigations.

Indicators of compromise (IoCs) and detection guidance

If your site runs eDS Responsive Menu (≤ 1.2), watch for these signs. Absence of these does not prove safety.

• Unexpected changes to wp_options entries, especially serialized values that look obfuscated.
• New admin users or changes to existing user roles/emails.
• New or modified PHP files in plugin/theme directories or PHP uploaded to wp-content/uploads.
• Unfamiliar scheduled tasks (WP-Cron) or server cron entries.
• Unusual outbound requests from the site to external domains.
• Errors/log entries referencing unserialize() or unexpected class autoloads.

How to scan and investigate:

• Use file integrity tools to compare files with clean WordPress core and trusted themes/plugins.
• Search the database for serialized object markers (e.g., patterns like O::”ClassName”).
• Review admin activity logs where available; enable logging if not present.
• Run multiple malware scanners (site-based and host-based) to reduce blind spots and false positives.
• If compromise is suspected, put the site into maintenance mode, take a full offline backup, and proceed with a controlled investigation.

Immediate actions for site owners (prioritized)

1. Confirm presence and version: Dashboard → Plugins → Installed Plugins. If eDS Responsive Menu exists and version ≤ 1.2, treat as vulnerable.
2. Lock down admin access: Temporarily disable unknown accounts, force password resets for all admins, require strong unique passwords, and enable MFA where possible.
3. Remove or replace the plugin: Deactivate and delete eDS Responsive Menu. Deleting plugin files removes code but may leave DB entries; review options table for residual data.
4. If immediate deletion isn’t possible: Restrict access to plugin endpoints using server-level rules (deny by path, restrict by IP) and disable remote administration where feasible.
5. Rotate credentials: Change all admin and service passwords, database credentials used by WordPress, and any API tokens.
6. Backup first: Take a full offline backup (files and DB) before further changes or investigations.
7. Scan thoroughly: Run file and database scans, inspect wp_options/wp_usermeta for suspicious serialized values, and look for unknown admin actions.
8. Monitor logs: Watch webserver, PHP, and WP activity logs for anomalous admin operations or imports.
9. Isolate if needed: If compromise is suspected, move the site to a staging environment for forensic work and restoration.

Developer guidance — fixing unserialize() safely

If your code uses unserialize() on potentially untrusted input, apply these measures:

• Avoid unserialize() on untrusted data. Prefer JSON (json_encode/json_decode) which does not instantiate PHP objects.
• If you must use unserialize(), use the allowed_classes option: unserialize($data, [‘allowed_classes’ => false]) to prevent object instantiation, or supply a strict allowlist.
• Validate and sanitize all inputs. Never trust POST, GET, cookies, or imported option data without strict checks.
• Enforce capability checks and nonces for any operation that modifies plugin settings (current_user_can(‘manage_options’) and wp_verify_nonce()).
• Avoid destructive side effects in magic methods (__wakeup, __destruct, __toString) — keep magic methods side-effect free.
• Use prepared statements for DB interactions ($wpdb->prepare()).
• Log and alert on significant admin-level changes to help detect suspicious activity early.

Why virtual patching and server rules matter when no vendor patch exists

When a vendor does not provide a patch, application-layer mitigations can reduce risk quickly:

• Server-level deny rules can block access to vulnerable plugin files or endpoints.
• A WAF (web application firewall) can be configured to block requests containing serialized PHP object patterns or suspicious POST payloads.
• Rate limiting and IP restrictions can reduce opportunity for exploitation from compromised accounts originating from unexpected locations.
• These measures reduce attack surface but do not replace fixing the underlying insecure code — removing or replacing the plugin remains the recommended long-term action.

Detailed remediation checklist (step-by-step)

1. Inventory & verification: Confirm plugin installation and version; list all admin/service accounts.
2. Containment: Put site into maintenance mode where feasible; deactivate and delete the plugin; if deletion isn’t immediately possible, restrict access to wp-admin and plugin paths by IP/server rules.
3. Credentials: Force admin password reset, enable MFA, rotate DB and API credentials.
4. Backup: Take a full offline backup before large changes.
5. Cleanup & validation: Scan and remove backdoors; delete unexpected PHP files; inspect and restore suspect serialized options from clean backups.
6. Monitoring & hardening: Enable logging of admin actions, schedule regular scans, and keep an inventory of plugins/themes in use.
7. Long-term: Replace abandoned plugins with maintained alternatives; review custom code for unsafe unserialize() usage and refactor.
8. If compromised: Consider professional incident response or rebuilding from a known clean codebase if persistence cannot be confidently removed.

Incident response: immediate steps if you suspect exploitation

• Isolate the site (take offline or restrict network access) where possible.
• Preserve logs and take forensic backups before making destructive changes.
• Consider restoring from a clean backup made before the suspected compromise, but ensure the root cause (vulnerable plugin or credential issue) is addressed prior to reconnecting.
• Engage experienced incident response or forensic practitioners if the compromise appears persistent or complex.
• Notify stakeholders (host, clients) according to your incident policies and any legal/regulatory requirements.

Why plugin abandonment increases risk

Abandoned plugins are risky because they no longer receive security patches, compatibility fixes, or support. They can:

• Remain vulnerable indefinitely.
• Introduce compatibility issues with newer PHP/WordPress versions that may surface additional bugs.
• Expand gadget availability for POI-style exploits when combined with other installed code.

Reduce dependency risk by preferring actively maintained plugins, regularly reviewing installed plugins, testing updates in staging, and keeping reliable backups and rollback plans.

Closing notes — security is an ongoing process

CVE-2025-58839 is a reminder: unserialized untrusted data is dangerous. Although the administrative requirement decreases the immediacy of remote automated compromise, weak or stolen admin credentials convert this into a significant operational risk. Practical steps are clear:

• Remove or replace unmaintained plugins promptly.
• Harden and rotate administrative credentials and enable MFA.
• Apply server-level or WAF mitigations while planning for permanent fixes or plugin replacement.
• Perform a full audit and adopt stronger operational security practices: logging, monitoring, limited admin privileges, and frequent backups.

If you require professional assistance, engage trusted incident response or managed security providers who have experience with WordPress compromises and forensic investigations.

— Hong Kong Security Expert

References and further reading

• PHP manual: unserialize() options and allowed_classes (search “unserialize allowed_classes”).
• OWASP: Injection categories and defensive guidance.
• WordPress hardening guides: admin credential best practices and capability checks.
• CVE record: CVE-2025-58839.