CVE-2026-97278 Overview
CVE-2026-97278 is a PHP Object Injection vulnerability in the WP SYNTEX Polylang plugin for WordPress. The flaw stems from deserialization of untrusted data [CWE-502] and affects all versions of Polylang up to and including 3.8.9. An authenticated attacker with high privileges can supply crafted serialized input to trigger object injection, leading to compromise of confidentiality, integrity, and availability of the affected WordPress site.
Polylang is a widely deployed multilingual plugin for WordPress, which increases the exposure surface for sites that have not applied the vendor fix. The vulnerability is exploitable over the network without user interaction.
Critical Impact
Successful exploitation enables arbitrary PHP object instantiation, which can be chained with gadget classes to achieve remote code execution, data tampering, or site takeover.
Affected Products
- WP SYNTEX Polylang plugin for WordPress
- All Polylang versions from n/a through 3.8.9
- WordPress sites with the vulnerable plugin activated
Discovery Timeline
- 2026-10-14 - CVE-2026-97278 published to NVD
- 2026-10-14 - Last updated in NVD database
Technical Details for CVE-2026-97278
Vulnerability Analysis
The vulnerability resides in a code path within the Polylang plugin that calls PHP's unserialize() on data that originates from an untrusted source. When PHP deserializes attacker-controlled input, it reconstructs objects of arbitrary classes available in the application's scope. Magic methods such as __wakeup(), __destruct(), and __toString() execute automatically during this process.
An attacker with high privileges in WordPress can abuse these magic methods by chaining gadgets from WordPress core, Polylang itself, or other installed plugins. These gadget chains can be weaponized for file writes, SQL execution, or arbitrary command execution.
The attack is network-reachable and requires no user interaction, which means a compromised administrator account or a lower-tier role elevated through a separate flaw can trigger the chain remotely.
Root Cause
The root cause is unsafe handling of serialized PHP data within Polylang code paths that process plugin configuration, language metadata, or request parameters. The plugin trusts serialized input and passes it directly to unserialize() without integrity validation or allow-listing of expected classes. This pattern is the canonical form of CWE-502, Deserialization of Untrusted Data.
Attack Vector
Exploitation requires an authenticated session with high privileges on the target WordPress instance. The attacker submits a crafted serialized payload through a plugin endpoint that reaches the vulnerable deserialization sink. The payload references a gadget chain whose magic methods perform the attacker's intended action during object reconstruction.
Technical analysis of the specific sink and gadget chain is documented in the Patchstack Vulnerability Report.
Detection Methods for CVE-2026-97278
Indicators of Compromise
- Unexpected PHP files, webshells, or modified theme and plugin files under wp-content/
- WordPress option or usermeta entries containing serialized objects referencing unexpected class names
- Outbound connections from the webserver to unknown hosts shortly after administrative actions
- New administrator accounts or role changes not tied to legitimate activity
Detection Strategies
- Inspect HTTP request bodies and query strings for serialized PHP markers such as O:, a:, and s: targeting Polylang endpoints
- Review web application firewall (WAF) logs for payloads matching PHP object injection signatures aimed at WordPress admin paths
- Audit the Polylang plugin version across managed WordPress estates and flag any instance at or below 3.8.9
Monitoring Recommendations
- Enable file integrity monitoring on wp-content/plugins/polylang/ and the WordPress core directories
- Forward WordPress and webserver logs to a centralized analytics pipeline for correlation of admin actions with process spawns
- Alert on PHP interpreter processes spawning shell binaries such as sh, bash, or curl from the webserver user context
How to Mitigate CVE-2026-97278
Immediate Actions Required
- Update the Polylang plugin to a version later than 3.8.9 as published by WP SYNTEX
- Rotate credentials for all WordPress administrator and editor accounts on affected sites
- Audit administrator sessions and recent plugin configuration changes for signs of abuse
- Review installed plugins and themes for known gadget chain classes that could be weaponized
Patch Information
Refer to the Patchstack Vulnerability Report for the fixed version and vendor advisory details. Apply the vendor patch across all WordPress environments, including staging and disaster recovery instances.
Workarounds
- Restrict administrative access to WordPress through IP allow-listing or VPN until the patch is applied
- Enforce multi-factor authentication (MFA) for all high-privilege WordPress accounts to limit attacker reach
- Deploy a WAF rule that blocks serialized PHP payloads submitted to Polylang request handlers
- Temporarily deactivate the Polylang plugin on sites where patching cannot be scheduled immediately
# Configuration example: WP-CLI commands to inventory and update Polylang
wp plugin get polylang --field=version
wp plugin update polylang
wp plugin list --status=active --format=table | grep polylang
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.