CVE-2020-37071: CraftCMS vCard Plugin RCE Vulnerability

CVE-2020-37071 Overview

CVE-2020-37071 is a critical insecure deserialization vulnerability affecting the CraftCMS 3 vCard Plugin version 1.0.0. This vulnerability allows unauthenticated attackers to execute arbitrary PHP code through a crafted serialized payload. By exploiting the plugin's vCard download functionality with a specially crafted request, attackers can trigger remote code execution on vulnerable CraftCMS installations.

Critical Impact

Unauthenticated remote code execution allows attackers to fully compromise CraftCMS installations, potentially leading to complete server takeover, data theft, and lateral movement within the network.

Affected Products

• CraftCMS 3 vCard Plugin version 1.0.0
• CraftCMS installations with the vulnerable vCard plugin enabled
• Web servers hosting affected CraftCMS deployments

Discovery Timeline

• 2026-02-03 - CVE-2020-37071 published to NVD
• 2026-02-04 - Last updated in NVD database

Technical Details for CVE-2020-37071

Vulnerability Analysis

This vulnerability is classified as CWE-502 (Deserialization of Untrusted Data), a critical class of vulnerabilities that can lead to remote code execution. The CraftCMS vCard Plugin fails to properly validate or sanitize user-supplied data before deserializing it, allowing attackers to inject malicious serialized PHP objects.

When the vCard download functionality processes a request, it deserializes user-controlled input without proper validation. An attacker can craft a malicious serialized payload containing PHP gadget chains that, when deserialized, execute arbitrary code on the server. This attack requires no authentication, making it particularly dangerous for internet-facing CraftCMS installations.

The network-accessible nature of this vulnerability combined with low attack complexity and no required user interaction makes it highly exploitable. Successful exploitation grants attackers the ability to execute arbitrary PHP code with the privileges of the web server process, potentially compromising confidentiality, integrity, and availability of the affected system.

Root Cause

The root cause of CVE-2020-37071 lies in the vCard Plugin's implementation of PHP's unserialize() function on untrusted user input. PHP object deserialization vulnerabilities occur when an application deserializes data from an untrusted source without proper validation. The vCard plugin processes incoming requests and deserializes payload data without implementing object type restrictions or input sanitization, allowing attackers to instantiate arbitrary PHP objects and invoke magic methods such as __wakeup() or __destruct() to achieve code execution.

Attack Vector

The attack vector is network-based and requires no authentication or user interaction. An attacker can exploit this vulnerability by sending a specially crafted HTTP request to the vCard download endpoint with a malicious serialized PHP payload. The exploitation process typically involves:

1. Identifying a target CraftCMS installation with the vulnerable vCard plugin
2. Generating a malicious serialized payload using known PHP gadget chains
3. Sending the crafted payload to the vCard download functionality endpoint
4. The server deserializes the malicious payload, triggering arbitrary PHP code execution

Technical details and proof-of-concept information are available through the GitLab CraftCMS VCard Exploit repository and the Exploit-DB #48492 entry.

Detection Methods for CVE-2020-37071

Indicators of Compromise

• Unusual HTTP requests targeting vCard download endpoints containing Base64-encoded or serialized data patterns
• Web server logs showing requests with PHP serialization markers (e.g., O:, a:, s: patterns in request parameters)
• Unexpected PHP processes spawning from web server contexts
• File system modifications or new files created in web-accessible directories
• Outbound network connections from the web server to unknown destinations

Detection Strategies

• Implement web application firewall (WAF) rules to detect and block serialized PHP objects in HTTP requests
• Deploy intrusion detection systems (IDS) with signatures for PHP deserialization attack patterns
• Monitor web server access logs for suspicious requests to vCard-related endpoints
• Enable PHP logging to capture errors related to object instantiation and deserialization failures
• Use runtime application self-protection (RASP) solutions to detect deserialization attacks

Monitoring Recommendations

• Configure alerting on web server logs for requests containing serialization patterns targeting CraftCMS endpoints
• Implement file integrity monitoring on CraftCMS installation directories to detect unauthorized modifications
• Monitor for anomalous PHP process behavior including unexpected child process spawning
• Set up network monitoring for unusual outbound connections from web server hosts

How to Mitigate CVE-2020-37071

Immediate Actions Required

• Disable or remove the CraftCMS vCard Plugin version 1.0.0 from all affected installations immediately
• Review web server logs for evidence of exploitation attempts targeting vCard endpoints
• Conduct a security assessment of affected servers to identify potential compromise
• Implement network segmentation to limit lateral movement if compromise is suspected
• Update CraftCMS and all plugins to the latest available versions

Patch Information

Organizations using the vulnerable CraftCMS vCard Plugin should check for updated versions that address this deserialization vulnerability. Consult the CraftCMS VCard Plugin page and the VulnCheck CraftCMS RCE Advisory for the latest patch information and security advisories. If no patched version is available, the plugin should be removed from production environments.

Workarounds

• Remove or disable the vCard plugin entirely until a patched version is available
• Implement WAF rules to block requests containing PHP serialized object patterns
• Restrict access to vCard download endpoints using server-level access controls
• Deploy input validation at the network perimeter to filter malicious serialized payloads

# Example Apache configuration to block vCard endpoints
<Location "/actions/vcard">
    Require all denied
</Location>

# Example nginx configuration to restrict vCard access
location ~* /actions/vcard {
    deny all;
    return 403;
}