CVE-2026-39918: Vvveb Code Injection RCE Vulnerability

CVE-2026-39918 Overview

CVE-2026-39918 is a critical code injection vulnerability affecting Vvveb prior to version 1.0.8.1. The vulnerability exists in the installation endpoint where the subdir POST parameter is written unsanitized into the env.php configuration file without proper escaping or validation. This flaw allows attackers to inject arbitrary PHP code by breaking out of the string context in the define statement, enabling unauthenticated remote code execution as the web server user.

Critical Impact

Unauthenticated attackers can achieve remote code execution on vulnerable Vvveb installations by exploiting the unsanitized subdir parameter during the installation process, potentially leading to complete system compromise.

Affected Products

• Vvveb versions prior to 1.0.8.1

Discovery Timeline

• April 20, 2026 - CVE-2026-39918 published to NVD
• April 20, 2026 - Last updated in NVD database

Technical Details for CVE-2026-39918

Vulnerability Analysis

This vulnerability is classified as CWE-94 (Improper Control of Generation of Code), commonly known as Code Injection. The flaw resides in how the Vvveb installation endpoint processes user-supplied input before writing it to a configuration file.

During the installation process, the application accepts a subdir parameter via POST request. This parameter is intended to define a subdirectory path for the application. However, the value is directly written into the env.php configuration file within a PHP define() statement without any sanitization, escaping, or validation.

Since the parameter is embedded within a string literal in a PHP define statement, an attacker can craft a malicious payload that breaks out of the string context. By injecting PHP code that closes the string and statement, then includes arbitrary code, followed by reopening the string context, the attacker can embed executable PHP code directly into the configuration file.

The attack is particularly dangerous because it requires no authentication—the installation endpoint is accessible to unauthenticated users, and successful exploitation results in code execution with the privileges of the web server user.

Root Cause

The root cause of this vulnerability is insufficient input validation and lack of output encoding when writing user-controlled data to an executable PHP configuration file. The subdir POST parameter is directly interpolated into a PHP define() statement without sanitizing special characters or escaping the input appropriately for the PHP string context.

Attack Vector

The attack is network-based and requires no authentication or user interaction. An attacker can send a specially crafted HTTP POST request to the installation endpoint with a malicious subdir parameter value. The payload breaks out of the PHP string context within the define() statement, allowing arbitrary PHP code to be written to the env.php configuration file. When this file is subsequently included by the application, the injected code executes with web server privileges.

The attack flow involves:

1. Identifying a vulnerable Vvveb installation (version prior to 1.0.8.1)
2. Sending a POST request to the installation endpoint with a crafted subdir value
3. The malicious value is written directly to env.php
4. When env.php is loaded, the injected PHP code executes

For detailed technical information about this vulnerability, see the VulnCheck Advisory.

Detection Methods for CVE-2026-39918

Indicators of Compromise

• Suspicious POST requests to the Vvveb installation endpoint containing unusual characters in the subdir parameter (e.g., quotes, semicolons, PHP tags)
• Unexpected modifications to the env.php configuration file, particularly content that includes PHP code beyond standard define statements
• Web server logs showing installation endpoint access from unexpected IP addresses or at unusual times
• Evidence of webshell activity or unauthorized commands executed as the web server user

Detection Strategies

• Monitor web server access logs for POST requests targeting the Vvveb installation endpoint with anomalous parameter values
• Implement file integrity monitoring on the env.php configuration file to detect unauthorized modifications
• Deploy web application firewall (WAF) rules to detect and block code injection patterns in POST parameters
• Use behavioral analysis to identify processes spawned by the web server that indicate post-exploitation activity

Monitoring Recommendations

• Enable detailed logging for web server access and error logs, particularly for installation-related endpoints
• Configure alerts for file changes to PHP configuration files in the Vvveb installation directory
• Monitor network traffic for outbound connections from the web server that may indicate a successful compromise
• Implement centralized log collection to correlate installation endpoint access with subsequent suspicious activity

How to Mitigate CVE-2026-39918

Immediate Actions Required

• Upgrade Vvveb to version 1.0.8.1 or later immediately
• If immediate patching is not possible, restrict access to the installation endpoint at the web server level
• Review env.php configuration files on existing installations for signs of injected PHP code
• Audit web server logs for any prior attempts to exploit this vulnerability

Patch Information

The vulnerability has been addressed in Vvveb version 1.0.8.1. The fix involves proper sanitization and validation of the subdir parameter before writing it to the configuration file. Organizations should update to this version or later to remediate the vulnerability.

• GitHub Release 1.0.8.1
• GitHub Commit with Fix

Workarounds

• Block access to the installation endpoint at the web server or firewall level if the installation process is complete
• Implement network segmentation to limit access to the Vvveb installation from trusted IP addresses only
• Set file permissions on env.php to read-only after installation is complete to prevent modification
• Deploy a WAF rule to filter POST requests containing PHP code patterns in the subdir parameter

# Example: Restrict access to installation endpoint via Apache .htaccess
<Files "install.php">
    Require ip 10.0.0.0/8
    Require ip 192.168.0.0/16
</Files>