CVE-2025-57919

Executive Summary

CVE-2025-57919 is a critical deserialization of untrusted data vulnerability in the ConveyThis WordPress plugin (conveythis-translate), affecting versions up to and including 269.1. This flaw allows an unauthenticated attacker to perform Object Injection by supplying malicious serialized data to the plugin’s deserialization routines. Successful exploitation can lead to remote code execution (RCE), full site compromise, data exfiltration, and lateral movement within the hosting environment. The vulnerability is classified under CWE-502 (Deserialization of Untrusted Data) and carries a CVSS score of 7.2 (High). No public proof-of-concept (PoC) or patch is currently available, making this a zero-day threat for all unpatched installations.

Supply Chain & Package Security

This vulnerability affects a WordPress plugin distributed via the official WordPress plugin repository. Organizations using ConveyThis should immediately audit their plugin version and treat the plugin as a high-risk supply chain component until a patch is released.

CVSS Breakdown & Threat Level

• Attack Vector (AV): Network (N) – Exploitable remotely.
• Attack Complexity (AC): Low (L) – No special conditions required.
• Privileges Required (PR): None (N) – No authentication needed.
• User Interaction (UI): None (N) – No user action required.
• Scope (S): Unchanged (U) – Exploit does not cross trust boundaries.
• Confidentiality (C): High (H) – Full data access possible.
• Integrity (I): High (H) – Full write access possible.
• Availability (A): High (H) – Full denial of service possible.

Threat Level: Critical (7.2) – Immediate action required.

Deep Dive & Mechanics

The vulnerability resides in the plugin’s handling of serialized PHP objects. The plugin likely uses unserialize() on user-supplied input without proper validation or sanitization. An attacker can craft a malicious serialized object that, when deserialized, triggers arbitrary PHP object instantiation and method execution (gadget chains). Common gadget chains in WordPress environments include those from the WP_Http class, Requests_Utility_FilteredIterator, or other core classes that implement __destruct, __wakeup, or __toString magic methods.

Attack Flow:

1. Attacker identifies an endpoint that passes user input to unserialize().
2. Attacker crafts a serialized payload containing a gadget chain.
3. Payload is sent via HTTP request (e.g., POST parameter, cookie, or file upload).
4. Plugin deserializes the payload, triggering the gadget chain.
5. Attacker achieves arbitrary code execution, file read/write, or database access.

Vulnerable vs. Patched Code

Since no patch is available, the vulnerable code pattern is speculative but typical:

Vulnerable (<= 269.1):

$data = $_POST['conveythis_data'];
$object = unserialize($data); // No validation

Patched (Hypothetical):

$data = $_POST['conveythis_data'];
$allowed_classes = ['ConveyThis\AllowedClass'];
$object = unserialize($data, ['allowed_classes' => $allowed_classes]);
// Or use json_decode() instead

Exploitation & Lab Setup

Red Team (Offensive)

Lab Environment:

• WordPress 6.x with ConveyThis plugin version 269.1
• PHP 7.4+ with allow_url_fopen enabled
• Attacker machine with PHPGGC (PHP Generic Gadget Chains)

Exploitation Steps:

1. Identify the vulnerable parameter (e.g., conveythis_data).
2. Generate a gadget chain using PHPGGC:

   phpggc WordPress/RCE1 system 'id' > payload.txt
   

3. Send the payload:

   curl -X POST http://target/wp-admin/admin-ajax.php \
     -d 'action=conveythis_process&conveythis_data='$(cat payload.txt)
   

4. Verify RCE by checking for command output in response or via out-of-band (OOB) exfiltration.

Note: No public exploit code is available; the above is a generic methodology.

Blue Team (Defensive)

Detection:

• Monitor for unserialize() calls in PHP error logs.
• Look for base64-encoded or serialized data in POST parameters.
• Deploy WAF rules to block serialized PHP objects (e.g., O:[0-9]+:" pattern).

Honeypot:

• Deploy a fake endpoint that logs all unserialize() attempts and alerts.

Indicators of Compromise (IOCs)

• Network: POST requests containing O:[0-9]+:" or a:[0-9]+:{ patterns.
• File System: Unexpected PHP files in /wp-content/uploads/ or /tmp/.
• Process: php processes executing with unusual arguments.
• Logs: PHP fatal errors related to unserialize() or class not found.
• Outbound: Connections to known C2 IPs or domains from the web server.

Detection Engineering

YARA Rule

rule CVE_2025_57919_Deserialization {
    meta:
        description = "Detects serialized PHP objects in HTTP requests targeting ConveyThis plugin"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-57919"
    strings:
        $serialized = /O:[0-9]+:"/
        $conveythis = "conveythis_data"
    condition:
        $serialized and $conveythis
}

Sigma Rule

title: CVE-2025-57919 ConveyThis Deserialization Attempt
id: 8a2b3c4d-5e6f-7a8b-9c0d-1e2f3a4b5c6d
status: experimental
description: Detects HTTP POST requests containing serialized PHP objects targeting ConveyThis plugin
author: Valters IT
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'POST'
        cs-uri-query|contains: 'conveythis_data'
        cs-uri-query|re: 'O:[0-9]+:"'
    condition: selection
falsepositives:
    - Legitimate plugin updates (rare)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-57919 ConveyThis Deserialization Attempt"; flow:to_server; content:"POST"; http_method; content:"conveythis_data"; http_client_body; pcre:"/O:[0-9]+:\"/"; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable the plugin until a patch is released.
2. Apply virtual patching via WAF to block serialized PHP objects.
3. Monitor logs for exploitation attempts using the provided detection rules.

Long-Term Fix:

• Replace unserialize() with json_decode() or use allowed_classes option.
• Implement input validation and sanitization for all user-supplied data.
• Conduct a security audit of the entire plugin codebase.

Workaround:

• If disabling is not possible, restrict access to the plugin’s AJAX endpoints via .htaccess:

  <FilesMatch "admin-ajax\.php">
      Order Deny,Allow
      Deny from all
  </FilesMatch>
  

Valters IT
Securing Digital Frontiers