CVE-2026-56037 Overview
CVE-2026-56037 is a PHP Object Injection vulnerability in the Themify Popup plugin for WordPress. The flaw stems from deserialization of untrusted data [CWE-502] and affects all versions of Themify Popup from initial release through 1.4.3. An authenticated attacker with low privileges can send crafted serialized payloads to trigger object instantiation within the plugin. When combined with a suitable POP (Property-Oriented Programming) chain in the WordPress environment, this leads to arbitrary code execution, data tampering, and denial of service on the target site.
Critical Impact
Authenticated attackers can inject malicious PHP objects to achieve remote code execution, resulting in full compromise of confidentiality, integrity, and availability on affected WordPress installations.
Affected Products
- Themify Popup plugin for WordPress
- Versions from n/a through 1.4.3
- WordPress sites running the vulnerable plugin with authenticated low-privilege user access
Discovery Timeline
- 2026-07-02 - CVE-2026-56037 published to NVD
- 2026-07-02 - Last updated in NVD database
Technical Details for CVE-2026-56037
Vulnerability Analysis
CVE-2026-56037 is an Insecure Deserialization vulnerability affecting the Themify Popup WordPress plugin. The plugin passes attacker-controlled input to a PHP deserialization function such as unserialize() without validating or restricting the resulting object types. This allows instantiation of arbitrary PHP objects during the deserialization process.
PHP Object Injection becomes exploitable when reachable classes define magic methods such as __wakeup(), __destruct(), or __toString() that perform sensitive operations. WordPress core and installed plugins provide a rich set of gadget classes that can be chained into a POP chain. Successful exploitation can trigger file writes, arbitrary function invocations, and remote code execution within the PHP process.
Root Cause
The root cause is direct deserialization of untrusted input received from an authenticated request context. The plugin does not enforce an allow-list of expected classes and does not use safer alternatives such as json_decode() for structured data. Any serialized payload delivered by a user with the required low-privilege role reaches the vulnerable code path.
Attack Vector
Exploitation is performed over the network against the WordPress site. The attacker must hold a valid low-privilege account, such as Subscriber or Contributor, depending on plugin routing. A serialized PHP payload is submitted through a plugin endpoint that invokes deserialization, and the crafted object graph executes the POP chain during unserialization. Refer to the Patchstack Vulnerability Report for advisory-level technical details.
Detection Methods for CVE-2026-56037
Indicators of Compromise
- HTTP POST requests to Themify Popup plugin endpoints containing serialized PHP strings such as payloads beginning with O:, a:, or s: in parameter values.
- Unexpected PHP processes spawning shell commands or writing files under wp-content/uploads/ or plugin directories.
- Creation of new administrator accounts, unknown scheduled tasks (wp_cron), or modified .htaccess files following plugin activity.
Detection Strategies
- Inspect web server and WordPress request logs for serialized object markers in parameters directed to Themify Popup routes.
- Monitor the WordPress plugin directory and wp-content for unexpected file modifications or new PHP files.
- Correlate authenticated user sessions against sudden privilege escalations or option table changes in wp_options.
Monitoring Recommendations
- Enable WordPress audit logging to capture plugin AJAX and REST endpoint activity with full parameter values.
- Deploy a web application firewall (WAF) rule that flags serialized PHP object patterns in request bodies.
- Alert on PHP-FPM or Apache child processes executing sh, bash, curl, or wget commands.
How to Mitigate CVE-2026-56037
Immediate Actions Required
- Update Themify Popup to a version later than 1.4.3 once the vendor releases a patched build.
- Restrict low-privilege user registration and audit existing accounts for unauthorized additions.
- Deploy WAF rules blocking serialized PHP payloads submitted to plugin endpoints.
Patch Information
At the time of publication, the advisory listed on Patchstack references vulnerable versions up to and including 1.4.3. Site administrators should consult the Patchstack Vulnerability Report and the vendor's plugin repository for updated fixed release information.
Workarounds
- Deactivate and remove the Themify Popup plugin until a patched version is installed.
- Apply a virtual patch via WAF to block requests containing PHP serialization tokens targeting plugin routes.
- Enforce least-privilege on WordPress roles and disable open user registration where feasible.
# Example WAF rule (ModSecurity) to block serialized PHP objects on plugin endpoints
SecRule REQUEST_URI "@contains /wp-admin/admin-ajax.php" \
"chain,phase:2,deny,status:403,id:1005603701,msg:'Themify Popup PHP Object Injection attempt'"
SecRule ARGS "@rx O:[0-9]+:\"[a-zA-Z_\\\\]+\":[0-9]+:" "t:none"
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
