CVE-2026-39539: Alloggio Hotel Booking Auth Bypass Flaw

CVE-2026-39539 Overview

CVE-2026-39539 is an unauthenticated PHP Object Injection vulnerability affecting the Alloggio - Hotel Booking WordPress theme through version 2.1.2. The flaw maps to [CWE-502: Deserialization of Untrusted Data] and allows remote attackers to inject crafted PHP serialized objects without authentication. Successful exploitation can compromise confidentiality, integrity, and availability of the WordPress site. Patchstack published the advisory tracking this issue against the affected theme. The vulnerability is network-accessible and requires no user interaction, though attack complexity is rated high.

Critical Impact
Unauthenticated attackers can inject malicious PHP objects into the Alloggio theme, potentially leading to remote code execution or full site compromise when a suitable gadget chain is available.

Affected Products

Alloggio - Hotel Booking WordPress theme versions <= 2.1.2
WordPress installations using the vulnerable theme
Hosting environments running PHP with the affected theme active

Discovery Timeline

2026-06-17 - CVE-2026-39539 published to NVD
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2026-39539

Vulnerability Analysis

The vulnerability stems from unsafe deserialization of attacker-controlled input within the Alloggio - Hotel Booking theme. PHP Object Injection occurs when user-supplied data reaches unserialize() without proper validation or filtering. Attackers craft serialized payloads that instantiate arbitrary PHP objects when the theme processes the input.

If the WordPress instance or any loaded plugin exposes a usable POP (Property-Oriented Programming) gadget chain, deserialization can escalate to file writes, file deletion, SQL injection, or remote code execution. The vulnerability requires no authentication and is reachable over the network, which broadens the attack surface to any internet-facing site running the affected theme.

The EPSS score for CVE-2026-39539 is 0.395%, indicating limited near-term exploitation forecasts despite the unauthenticated attack path.

Root Cause

The root cause is improper handling of serialized input passed to PHP deserialization routines inside the theme code. The theme accepts data from untrusted sources and deserializes it without verifying structure, origin, or integrity. This violates safe deserialization practice and exposes the application to object injection [CWE-502].

Attack Vector

An unauthenticated attacker sends a crafted HTTP request to an endpoint exposed by the Alloggio theme. The request contains a serialized PHP object designed to trigger magic methods such as __wakeup, __destruct, or __toString during deserialization. When combined with a gadget chain present in WordPress core, plugins, or the theme itself, the attacker can pivot from object instantiation to code execution or data tampering.

For verified technical details, refer to the Patchstack WordPress Vulnerability advisory.

Detection Methods for CVE-2026-39539

Indicators of Compromise

Unexpected HTTP POST or GET requests containing serialized PHP patterns such as O:, a:, or s: in parameter values
New or modified PHP files in wp-content/themes/alloggio/ or wp-content/uploads/
Unscheduled outbound connections from the PHP-FPM or web server process
WordPress administrator accounts or options table entries created without an audit trail

Detection Strategies

Inspect web server access logs for requests targeting Alloggio theme endpoints with serialized object signatures
Enable PHP error and audit logging to flag unserialize() failures or unexpected class instantiation
Deploy WAF rules that block serialized PHP payloads in request bodies and query strings
Compare theme file hashes against a known-good baseline of version 2.1.2 or later patched releases

Monitoring Recommendations

Monitor for anomalous child processes spawned by the web server user, such as sh, bash, or curl
Track outbound network traffic from web hosts to non-business destinations
Alert on modifications to WordPress core files, theme files, and the wp_options table

How to Mitigate CVE-2026-39539

Immediate Actions Required

Identify all WordPress sites running the Alloggio - Hotel Booking theme at version <= 2.1.2
Apply the vendor-supplied patched release as soon as it is available from the theme author or Patchstack
Place a WAF in front of affected sites to filter serialized PHP payloads pending patch deployment
Review web and application logs for prior exploitation attempts referencing the vulnerable theme paths

Patch Information

Consult the Patchstack advisory for the Alloggio theme for the latest patched version and remediation guidance. Upgrade beyond version 2.1.2 once the vendor publishes a fix, and verify the upgrade using checksum comparison.

Workarounds

Deactivate and remove the Alloggio - Hotel Booking theme until a patched version is installed
Apply virtual patching through a WordPress firewall plugin or upstream WAF to block PHP object injection signatures
Restrict access to vulnerable theme endpoints via web server access controls where business operations allow

bash

# Example WAF rule pattern to block serialized PHP objects in request bodies
SecRule ARGS "@rx (^|&)[^=]*=O:\d+:\"[A-Za-z0-9_\\\\]+\":\d+:\{" \
  "id:1039539,phase:2,deny,status:403,msg:'Possible PHP Object Injection - CVE-2026-39539'"