CVE-2026-27429: Nifty PHP Object Injection Vulnerability

CVE-2026-27429 Overview

CVE-2026-27429 is an unauthenticated PHP Object Injection vulnerability affecting the Nifty WordPress theme in versions up to and including 1.4.1. The flaw is rooted in insecure deserialization of untrusted input [CWE-502]. An unauthenticated remote attacker can submit crafted serialized data to a vulnerable endpoint and trigger instantiation of arbitrary PHP objects within the application context. When a suitable gadget chain is present in WordPress core, the active theme, or installed plugins, this primitive can be escalated to file write, file read, deletion, or remote code execution on the host.

Critical Impact
Unauthenticated attackers can inject PHP objects over the network, leading to potential remote code execution, data disclosure, and full compromise of WordPress sites running the Nifty theme versions 1.4.1 and earlier.

Affected Products

Nifty WordPress Theme versions <= 1.4.1
WordPress installations with the Nifty theme active
Sites bundling plugins that introduce exploitable PHP gadget chains alongside Nifty

Discovery Timeline

2026-06-17 - CVE-2026-27429 published to the National Vulnerability Database
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2026-27429

Vulnerability Analysis

The Nifty theme passes attacker-controlled input into a PHP deserialization routine without validating the data source or restricting the classes allowed during reconstruction. PHP Object Injection occurs when unserialize() (or an equivalent path) operates on untrusted bytes, instantiating arbitrary objects and invoking their magic methods such as __wakeup, __destruct, or __toString.

Because the vulnerable code path does not require authentication, any remote actor able to reach the WordPress site can deliver a payload. Exploitation severity depends on the gadget chains available in loaded code. WordPress environments frequently ship with classes that, when reconstructed in a hostile order, produce arbitrary file operations or command execution. The reported impact spans confidentiality, integrity, and availability.

Root Cause

The root cause is unsafe deserialization of untrusted input within the Nifty theme codebase [CWE-502]. Input flowing from an HTTP request reaches a deserialization sink without an allow-list of permitted classes and without integrity verification such as a signed payload or HMAC.

Attack Vector

The attack is network-based and requires no privileges or user interaction. An attacker crafts a serialized PHP payload that references gadget classes resident in the WordPress runtime. The payload is delivered through the vulnerable Nifty parameter, parsed by PHP, and triggers gadget execution during object construction or destruction. The vulnerability mechanics are documented in the Patchstack WordPress Vulnerability Report.

Detection Methods for CVE-2026-27429

Indicators of Compromise

HTTP request bodies or query parameters containing serialized PHP markers such as O:, a:, or s: followed by class names and lengths
Unexpected file writes under wp-content/uploads/, wp-content/themes/nifty/, or other theme and plugin directories
New or modified PHP files containing webshell patterns following requests to Nifty theme endpoints
Outbound network connections initiated by the PHP-FPM or web server process to unfamiliar hosts

Detection Strategies

Inspect web server access logs for requests targeting Nifty theme endpoints carrying serialized object signatures in parameters or POST bodies
Deploy Web Application Firewall (WAF) rules that flag PHP serialization tokens in user input where they are not expected
Correlate anomalous PHP process behavior, such as spawning shell interpreters or writing executable files, with prior Nifty theme HTTP traffic

Monitoring Recommendations

Enable file integrity monitoring on the WordPress document root, with priority on wp-content/themes/ and wp-content/plugins/
Centralize PHP error logs and alert on warnings related to unserialize() and undefined class references
Monitor outbound egress from the web tier and alert on connections to non-allowlisted destinations

How to Mitigate CVE-2026-27429

Immediate Actions Required

Upgrade the Nifty theme to a fixed release published after version 1.4.1, as identified in the Patchstack advisory
Audit affected WordPress sites for signs of post-exploitation activity, including unauthorized administrators, modified theme files, and unexpected scheduled tasks
Rotate WordPress secrets in wp-config.php and reset administrative credentials if compromise is suspected

Patch Information

Refer to the Patchstack WordPress Vulnerability Report for the authoritative fixed version and vendor remediation details. Apply the update through the WordPress admin interface or by replacing the theme directory with the patched release.

Workarounds

Disable the Nifty theme and switch to an unaffected theme until the patch is applied
Place a WAF rule in front of the site that blocks request parameters containing serialized PHP object signatures
Restrict the web server process with least-privilege file system permissions to limit the impact of arbitrary file operations

bash

# Example ModSecurity rule to block PHP serialized payloads in request bodies
SecRule REQUEST_BODY|ARGS "@rx (?:^|[=&])(?:O|a|s):\d+:\"" \
    "id:1027429,phase:2,deny,status:403,log,\
    msg:'Potential PHP Object Injection payload (CVE-2026-27429)'"