CVE-2026-12378 Overview
CVE-2026-12378 is a PHP Object Injection vulnerability in the Appointment Booking Calendar Plugin and Scheduling Plugin for WordPress through version 1.1.28. The plugin passes untrusted input to a PHP deserialization function without validation. Unauthenticated attackers can inject arbitrary PHP objects into the application. When a suitable gadget chain exists on the target site, this can escalate to remote code execution (RCE).
Critical Impact
Unauthenticated remote attackers can inject PHP objects and, given a viable gadget chain, achieve full remote code execution on the WordPress host.
Affected Products
- Appointment Booking Calendar Plugin and Scheduling Plugin for WordPress
- All versions through 1.1.28
- WordPress sites running the vulnerable plugin with additional plugins or themes providing gadget chains
Discovery Timeline
- 2026-07-08 - CVE-2026-12378 published to the National Vulnerability Database (NVD)
- 2026-07-08 - Last updated in NVD database
Technical Details for CVE-2026-12378
Vulnerability Analysis
The vulnerability is an Insecure Deserialization flaw ([CWE-502]) affecting the plugin's request handling logic. The plugin accepts attacker-controlled data and forwards it directly to a PHP deserialization sink such as unserialize(). During deserialization, PHP reconstructs objects and invokes magic methods including __wakeup() and __destruct(). Attackers craft serialized payloads that instantiate classes already loaded in WordPress core, other plugins, or themes. When these classes contain exploitable side effects, the deserialization triggers file writes, SQL execution, or arbitrary command execution.
The attack complexity is elevated because successful RCE requires a viable POP (Property-Oriented Programming) gadget chain in the target environment. Sites running common plugins that expose known gadget chains face the highest risk. Even without RCE, object injection can enable authentication bypass, data tampering, or denial of service.
Root Cause
The root cause is the direct use of unserialize() on untrusted user input without prior validation, allow-listing, or migration to a safe format such as JSON. The plugin does not restrict input types, verify signatures, or use the allowed_classes option introduced in PHP 7.
Attack Vector
The attack vector is network-based and requires no authentication or user interaction. An attacker sends a crafted HTTP request containing a serialized PHP object payload to a vulnerable plugin endpoint. The plugin deserializes the payload, and any magic methods on the injected classes execute in the WordPress context. See the WPScan Vulnerability Report for endpoint specifics.
No verified public exploit code is available at the time of publication. Deserialization vulnerabilities in WordPress plugins are described in vendor documentation and community research.
Detection Methods for CVE-2026-12378
Indicators of Compromise
- HTTP POST or GET requests to the plugin endpoints containing serialized PHP object markers such as O:, a:, or s: in parameter values
- Unexpected PHP file creation under wp-content/uploads/ or plugin directories following requests to the booking plugin
- Outbound network connections initiated by the php-fpm or web server process to unfamiliar hosts
- New administrator accounts or modified wp_users and wp_options entries without corresponding admin activity
Detection Strategies
- Inspect web server access logs for request parameters matching the PHP serialization grammar, particularly O:\d+:" patterns targeting the plugin URLs
- Deploy a Web Application Firewall (WAF) rule set that flags serialized payloads in query strings, POST bodies, and cookies
- Monitor WordPress file integrity to detect unauthorized modifications to core files, themes, or plugins
- Correlate deserialization payload signatures with subsequent process spawns from the web server user
Monitoring Recommendations
- Enable verbose logging on the WordPress instance and forward logs to a centralized SIEM for parsing
- Alert on child processes spawned by the PHP interpreter such as sh, bash, curl, or wget
- Track outbound DNS and HTTP traffic from web hosts to identify command-and-control callbacks
How to Mitigate CVE-2026-12378
Immediate Actions Required
- Disable or remove the Appointment Booking Calendar Plugin until a fixed version is installed
- Restrict access to the WordPress site using IP allow-listing or authentication in front of vulnerable endpoints
- Audit installed plugins and themes to reduce the presence of exploitable gadget chains
- Review WordPress admin accounts and recent file changes for signs of prior exploitation
Patch Information
No vendor patch is referenced in the NVD entry at the time of publication. Site administrators should monitor the plugin listing on WordPress.org and the WPScan Vulnerability Report for updates beyond version 1.1.28.
Workarounds
- Deploy WAF rules that block requests containing PHP serialization patterns in parameters submitted to the plugin
- Uninstall the plugin and replace it with an actively maintained booking solution if a patch is not released promptly
- Apply least-privilege configuration to the PHP-FPM user to limit the impact of successful code execution
# Example ModSecurity rule to block PHP serialized objects in request bodies
SecRule ARGS "@rx O:[0-9]+:\"[a-zA-Z_\\\\]+\":[0-9]+:" \
"id:1012378,phase:2,deny,status:403,log,\
msg:'CVE-2026-12378 PHP object injection attempt'"
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
