CVE-2022-50898: NanoCMS 0.4 Authenticated RCE Vulnerability

CVE-2022-50898 Overview

CVE-2022-50898 is an authenticated file upload vulnerability affecting NanoCMS version 0.4. This vulnerability enables remote code execution through unvalidated page content creation. Authenticated attackers can upload PHP files containing arbitrary code to the server's pages directory by exploiting the page creation mechanism, which lacks proper input sanitization. This type of code injection vulnerability (CWE-94) poses significant risk to organizations running vulnerable NanoCMS installations.

Critical Impact

Authenticated attackers can achieve complete server compromise by uploading malicious PHP files through the unsanitized page creation functionality, potentially leading to full system takeover and data exfiltration.

Affected Products

• NanoCMS 0.4

Discovery Timeline

• 2026-01-13 - CVE-2022-50898 published to NVD
• 2026-01-13 - Last updated in NVD database

Technical Details for CVE-2022-50898

Vulnerability Analysis

This vulnerability exists within the page creation functionality of NanoCMS 0.4, a lightweight content management system. The core issue stems from the application's failure to properly validate and sanitize user-supplied content during page creation operations. When an authenticated user creates a new page, the application writes the content directly to PHP files in the pages directory without implementing appropriate security controls.

The attack requires valid authentication credentials, but once authenticated, an attacker can craft page content containing malicious PHP code. Since the CMS stores page content as .php files without stripping or escaping executable code, the malicious payload becomes directly executable on the web server. This allows attackers to run arbitrary commands with the privileges of the web server process.

Root Cause

The root cause of CVE-2022-50898 is improper input validation (CWE-94 - Improper Control of Generation of Code). The NanoCMS page creation mechanism fails to implement proper content sanitization, allowing PHP code to be embedded within page content. The application directly writes user-controlled input to PHP files without stripping dangerous constructs such as <?php tags or other executable code patterns. This fundamental lack of input validation creates a direct path from authenticated user input to server-side code execution.

Attack Vector

The attack is network-accessible and requires authenticated access to the NanoCMS administrative interface. An attacker must first obtain valid credentials, either through credential theft, brute force attacks, or exploitation of weak default credentials. Once authenticated, the attacker navigates to the page creation functionality and injects malicious PHP code within the page content field.

When the page is saved, NanoCMS writes this content to a .php file in the pages directory. The attacker can then access this newly created page via a direct HTTP request, triggering execution of the injected PHP code. Common payloads include web shells, reverse shells, or code designed to establish persistent access to the compromised system.

For technical exploitation details, refer to the Exploit-DB entry for this vulnerability and the VulnCheck advisory.

Detection Methods for CVE-2022-50898

Indicators of Compromise

• Unexpected .php files appearing in the NanoCMS pages directory with suspicious content patterns
• Web server logs showing direct access to non-standard page files immediately after administrative page creation
• Presence of PHP files containing shell command functions such as system(), exec(), passthru(), or shell_exec()
• Evidence of outbound connections from the web server to unknown external hosts

Detection Strategies

• Monitor file system changes in the NanoCMS pages directory for creation of new PHP files with executable code patterns
• Implement web application firewall (WAF) rules to detect common PHP web shell signatures in HTTP POST requests
• Deploy endpoint detection to identify web shell behavior such as command execution spawned from web server processes
• Review authentication logs for suspicious login patterns that may indicate credential compromise preceding exploitation

Monitoring Recommendations

• Enable file integrity monitoring on the NanoCMS installation directory, particularly the pages subdirectory
• Configure security information and event management (SIEM) alerts for PHP file creation events correlated with administrative actions
• Monitor web server process trees for unexpected child processes indicating command execution

How to Mitigate CVE-2022-50898

Immediate Actions Required

• Audit existing NanoCMS installations and review the pages directory for any suspicious or unexpected PHP files
• Implement strict access controls limiting administrative access to trusted IP addresses only
• Consider disabling NanoCMS page creation functionality until a patch is available or migration is complete
• Review authentication logs for signs of unauthorized access or credential compromise

Patch Information

No official vendor patch has been identified in the available CVE data. NanoCMS 0.4 is a legacy application, and users should consider migrating to a maintained content management system with active security support. For additional technical details, consult the NanoCMS GitHub repository and the VulnCheck advisory.

Workarounds

• Implement application-layer filtering to strip PHP tags and executable constructs from page content before saving
• Restrict file permissions on the pages directory to prevent PHP execution if operationally feasible
• Deploy a web application firewall with rules specifically targeting PHP code injection patterns
• Migrate to an actively maintained CMS platform with proper input validation and security controls

# Example: Restrict PHP execution in pages directory via Apache
# Add to .htaccess in the NanoCMS pages directory
<Directory /var/www/html/nanocms/pages>
    php_flag engine off
    RemoveHandler .php .phtml .php3 .php4 .php5 .phps
    AddType text/plain .php .phtml .php3 .php4 .php5 .phps
</Directory>