CVE-2026-57621: Booktics Auth Bypass Vulnerability

CVE-2026-57621 Overview

CVE-2026-57621 is an unauthenticated PHP Object Injection vulnerability affecting the Booktics WordPress plugin in versions 1.0.21 and earlier. The flaw stems from insecure deserialization [CWE-502] of attacker-controlled input, allowing remote adversaries to inject arbitrary PHP objects into the application. When combined with a suitable POP (Property-Oriented Programming) chain from the plugin, WordPress core, or another installed component, exploitation can lead to remote code execution, arbitrary file operations, or full site compromise. No authentication or user interaction is required, and the attack is delivered over the network.

Critical Impact
Unauthenticated attackers can trigger PHP object deserialization on vulnerable Booktics installations, enabling remote code execution when a viable gadget chain is present.

Affected Products

Booktics WordPress plugin versions <= 1.0.21
WordPress sites running the vulnerable Booktics plugin
Any hosting environment exposing the affected plugin endpoints to the internet

Discovery Timeline

2026-07-02 - CVE-2026-57621 published to NVD
2026-07-02 - Last updated in NVD database

Technical Details for CVE-2026-57621

Vulnerability Analysis

The vulnerability is an unauthenticated PHP Object Injection issue in the Booktics plugin. PHP Object Injection occurs when user-supplied data reaches a unserialize() call without validation. During deserialization, PHP reconstructs object instances and invokes magic methods such as __wakeup(), __destruct(), and __toString(). Attackers craft serialized payloads that instantiate classes whose magic methods perform sensitive operations, chaining these into a gadget that achieves code execution, file writes, or database manipulation.

Because the endpoint is reachable without authentication, an attacker only needs network access to the WordPress site. The 1.0.21 and prior releases fail to sanitize or reject serialized input before passing it to a deserialization routine, exposing the site to remote compromise.

Root Cause

The root cause is improper handling of serialized data [CWE-502]. The plugin deserializes untrusted input from a request parameter, cookie, or stored value without integrity checks or type constraints. PHP's unserialize() is inherently unsafe on untrusted data because it triggers class autoloading and magic methods during object reconstruction.

Attack Vector

An attacker sends a crafted HTTP request containing a serialized PHP object payload to a vulnerable Booktics endpoint. The plugin passes the payload to unserialize(), and the reconstructed object executes attacker-controlled logic through a gadget chain. Available chains from WordPress core, other plugins, or PHP libraries such as Monolog and Guzzle are commonly abused to escalate object injection to remote code execution.

The vulnerability manifests during deserialization of unauthenticated input. See the Patchstack Vulnerability Report for additional technical context.

Detection Methods for CVE-2026-57621

Indicators of Compromise

HTTP request bodies or query parameters containing serialized PHP structures such as O:8:"stdClass", a:1:{, or class names prefixed with O:.
Unexpected PHP processes spawning shells, curl, or wget from the web server user (www-data, apache, nginx).
New or modified PHP files in wp-content/uploads/ or plugin directories with recent timestamps.
Outbound connections from the WordPress host to unknown IP addresses shortly after suspicious POST requests.

Detection Strategies

Inspect web server and WAF logs for serialized payload patterns matching O:\d+:"[A-Za-z_]+" in request parameters targeting Booktics endpoints.
Alert on WordPress file integrity changes, especially additions to plugin, theme, or uploads directories.
Correlate unauthenticated POST requests to Booktics with subsequent process creation events on the underlying host.

Monitoring Recommendations

Enable verbose access logging on all WordPress sites running Booktics until patched or removed.
Monitor PHP error logs for unserialize() warnings and unexpected class instantiation failures.
Track child processes spawned by php-fpm or the web server and alert on shell interpreters or network utilities.

How to Mitigate CVE-2026-57621

Immediate Actions Required

Deactivate and remove the Booktics plugin if a patched version is not yet available for your environment.
Restrict access to WordPress admin and plugin endpoints using IP allowlists or a web application firewall.
Review WordPress installations for unauthorized administrator accounts, scheduled tasks (wp_cron), and modified files.

Patch Information

At the time of publication, the Patchstack advisory lists Booktics <= 1.0.21 as vulnerable. Site administrators should upgrade to a fixed release once the vendor publishes one, and consult the Patchstack Vulnerability Report for the latest remediation guidance.

Workarounds

Block requests containing serialized PHP payloads at the WAF by matching regex patterns such as O:\d+:" and a:\d+:\{ in body and query strings.
Isolate the WordPress site behind authentication or a VPN if it is not required to be publicly accessible.
Use a virtual patching rule from your WAF vendor that specifically targets CVE-2026-57621 until a plugin update is applied.

bash

# Example ModSecurity rule to block serialized PHP payloads targeting Booktics endpoints
SecRule REQUEST_URI "@contains /wp-content/plugins/booktics/" \
  "id:1057621,phase:2,deny,status:403,log,\
   msg:'Potential CVE-2026-57621 PHP Object Injection attempt',\
   chain"
  SecRule ARGS|REQUEST_BODY "@rx O:\d+:\"[A-Za-z_\\\\]+\":\d+:\{" \
    "t:none"