CVE-2025-39495 Overview
CVE-2025-39495 is a PHP Object Injection vulnerability in the BoldThemes Avantage WordPress theme. The flaw stems from deserialization of untrusted data [CWE-502] and affects all versions up to and including 2.4.9. Unauthenticated attackers can submit crafted serialized payloads to vulnerable endpoints. When the theme calls unserialize() on attacker-controlled input, PHP instantiates arbitrary objects and triggers magic methods. This behavior enables object injection attack chains that can lead to remote code execution, file manipulation, or data exfiltration depending on installed plugins and available gadgets.
Critical Impact
Unauthenticated attackers can trigger PHP object injection over the network, potentially leading to remote code execution on WordPress sites running the Avantage theme through version 2.4.9.
Affected Products
- BoldThemes Avantage WordPress theme versions through 2.4.9
- WordPress installations using the Avantage theme as active or inactive
- Sites where the Avantage theme files remain accessible on disk
Discovery Timeline
- 2025-05-23 - CVE-2025-39495 published to the National Vulnerability Database (NVD)
- 2026-04-23 - Last updated in NVD database
Technical Details for CVE-2025-39495
Vulnerability Analysis
The vulnerability is classified as Insecure Deserialization leading to Object Injection [CWE-502]. The Avantage theme passes attacker-controlled input to PHP's unserialize() function without validation or integrity checks. PHP rebuilds the object graph from the serialized string and invokes magic methods such as __wakeup(), __destruct(), and __toString() during the process.
Attackers craft payloads that reference classes already loaded by WordPress core, other plugins, or themes. These classes form gadget chains where method side effects produce attacker-controlled behavior. Outcomes include arbitrary file write, file deletion, SQL injection, server-side request forgery, or remote code execution.
The attack requires no authentication and no user interaction. The network attack vector means any reachable WordPress site running a vulnerable Avantage version is exposed.
Root Cause
The root cause is the use of unserialize() on data sourced from HTTP requests, cookies, or other client-controlled channels. The theme does not validate input format, restrict allowed classes, or use safe alternatives such as json_decode(). The Patchstack advisory documents the issue against Avantage version 2.4.6 and confirms exposure through version 2.4.9.
Attack Vector
An unauthenticated remote attacker sends an HTTP request containing a crafted serialized PHP object to a vulnerable Avantage endpoint. The theme deserializes the payload, triggering magic methods on attacker-chosen classes. Available gadget chains determine the final impact, which can escalate to full site compromise when suitable classes exist in the WordPress runtime.
No verified exploit code or public proof of concept is currently linked to this CVE. Refer to the Patchstack WordPress Vulnerability advisory for additional technical context.
Detection Methods for CVE-2025-39495
Indicators of Compromise
- HTTP requests containing serialized PHP markers such as O: (object), a: (array), or s: (string) in POST bodies, query parameters, or cookies targeting Avantage theme endpoints.
- Unexpected PHP processes spawning shell utilities such as sh, bash, or curl from the WordPress web server context.
- New or modified PHP files under wp-content/themes/avantage/ or wp-content/uploads/ outside of administrator activity.
- Outbound network connections from the WordPress host to unfamiliar IP addresses immediately after suspicious requests.
Detection Strategies
- Inspect web server access logs for requests to Avantage theme paths containing URL-encoded serialized payloads.
- Deploy a web application firewall rule that blocks request parameters matching PHP serialization patterns like O:\d+:".
- Monitor file integrity on theme, plugin, and uploads directories to detect unauthorized PHP file creation.
Monitoring Recommendations
- Alert on PHP-FPM or Apache worker processes executing child processes that are not part of normal WordPress operation.
- Track outbound HTTP, DNS, and TCP connections from web servers and flag connections to unfamiliar destinations.
- Correlate authentication logs with administrative actions to identify privilege escalation following suspicious requests.
How to Mitigate CVE-2025-39495
Immediate Actions Required
- Identify all WordPress sites running the BoldThemes Avantage theme at version 2.4.9 or earlier and prioritize remediation.
- Apply the vendor patch as soon as a fixed version is published by BoldThemes.
- Deploy WAF rules that block serialized PHP object patterns in untrusted request inputs.
- Audit wp-content/themes/, wp-content/plugins/, and wp-content/uploads/ for unauthorized PHP files and modifications.
Patch Information
At the time of publication, the NVD entry lists affected versions through 2.4.9 with no fixed version recorded in this dataset. Monitor the Patchstack WordPress Vulnerability advisory and the BoldThemes vendor channels for an updated theme release that removes the unserialize() call on untrusted input.
Workarounds
- Disable and remove the Avantage theme until a patched version is available, switching to a maintained theme.
- Restrict access to theme endpoints at the web server or WAF layer to known administrator IP ranges.
- Use a virtual patching solution such as Patchstack or a managed WAF to block known object injection payloads.
# Example ModSecurity rule to block serialized PHP object payloads
SecRule ARGS|REQUEST_COOKIES|REQUEST_HEADERS "@rx O:\d+:\"[A-Za-z_\\\\]+\":\d+:" \
"id:1003949,phase:2,deny,status:403,log,msg:'PHP Object Injection attempt (CVE-2025-39495)'"
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
