CVE-2026-39539: Critical PHP Object Injection in Alloggio Hotel Booking Plugin ≤ 2.1.2

Technical summary

CVE-2026-39539 exploits unsafe PHP object deserialization (CWE-502) in Alloggio Hotel Booking. The vulnerability allows an unauthenticated remote attacker to craft a malicious serialized PHP object and inject it via an unprotected endpoint. When the application deserializes this object without validation, it can trigger existing PHP magic methods or gadget chains to achieve arbitrary code execution. The CVSS 3.1 score of 8.1 reflects the attack complexity (AC:H suggests some specific conditions must be met), but the lack of authentication requirements and network accessibility make this highly exploitable in practice.

Business impact

A successful exploit could result in complete compromise of the hotel booking website, including theft of guest payment data, reservation information, and personal details. Attackers could modify or delete bookings, inject malicious content for phishing guests, or pivot to backend infrastructure. For hotel operators relying on this plugin, remediation delays create ongoing risk of financial loss, regulatory exposure under PCI-DSS and similar standards, and reputational harm.

Affected systems

Alloggio Hotel Booking plugin versions 2.1.2 and earlier are vulnerable. This affects WordPress installations using this plugin. Verify your version by checking the plugin settings or repository listing. The vulnerability is network-accessible without authentication, making every unpatched instance exposed by default.

Exploitability

Exploitation requires network access and the ability to send crafted HTTP requests to the vulnerable endpoint—both typically available to unauthenticated users on the internet. Although the CVSS attack complexity is marked as 'High,' this likely reflects specific object gadget chain requirements rather than practical difficulty; attackers with knowledge of the plugin's PHP dependencies or publicly available gadget chains can exploit this reliably. No authentication, user interaction, or privileged access is required.

Remediation

Immediately update Alloggio Hotel Booking to a patched version released after 2.1.2. Check the official plugin repository or vendor advisory for the latest secure release. If an update is unavailable, consider disabling the plugin temporarily and using an alternative booking solution. Validate that all site files are restored from a clean backup or verified against vendor checksums—assume compromise and review logs and admin accounts if the site was exposed.

Patch guidance

Visit the WordPress plugin repository or the Alloggio vendor's official website to download the latest patched version. Update via the WordPress admin dashboard: navigate to Plugins → Installed Plugins, locate Alloggio Hotel Booking, and click 'Update Now'. After patching, flush any object caches and verify the site functions normally. Document the patch date and version for compliance records. Verify against the vendor advisory to confirm the released version number addresses CWE-502 object injection.

Detection guidance

Monitor web server logs for unusual HTTP requests to plugin endpoints, particularly those containing serialized PHP objects (strings beginning with 'O:', 'C:', or 'a:' patterns in URL parameters or POST bodies). Search web application firewall rules for PHP deserialization signatures. Review WordPress plugin integrity logs and check for unauthorized file modifications in the plugin directory. Examine database change logs for suspicious booking records or injected content. Consider running vulnerability scanners (e.g., WPScan) with current CVE definitions to confirm version status across your WordPress installations.

Why prioritize this

This vulnerability scores HIGH (8.1/10) due to the combination of unauthenticated remote access, significant impact potential (confidentiality, integrity, and availability), and likely broad exposure of hotel booking sites. The lack of KEV designation does not diminish urgency—many organizations only prioritize KEV-listed issues, but active exploitation of unpatched object injection flaws is common. Hotel booking platforms typically hold sensitive payment and guest data, elevating business risk. Patching should be treated as critical-priority work.

Risk score, explained

The CVSS 3.1 score of 8.1 (HIGH) reflects: Network-accessible attack vector (AV:N), no authentication required (PR:N), no user interaction needed (UI:N), single impacted system scope (S:U), and high impact across confidentiality (C:H), integrity (I:H), and availability (A:H). Attack complexity is marked High (AC:H), likely due to the need for a specific gadget chain or plugin configuration, but this does not materially reduce exploitability for informed attackers. The score appropriately signals critical-to-high business priority.

Frequently asked questions