CVE-2026-33029: Nginx UI Denial of Service Vulnerability

CVE-2026-33029 Overview

CVE-2026-33029 is an input validation vulnerability affecting Nginx UI, a web user interface for the Nginx web server. Prior to version 2.3.4, the logrotate configuration functionality fails to properly validate user input, allowing an authenticated user to cause a complete Denial of Service (DoS). By submitting a negative integer for the rotation interval, the backend enters an infinite loop or an invalid state, rendering the web interface completely unresponsive.

Critical Impact

Authenticated attackers can render Nginx UI completely unresponsive by exploiting improper input validation in logrotate configuration, leading to service disruption and potential operational impact.

Affected Products

• Nginx UI versions prior to 2.3.4
• nginxui nginx_ui (all versions before patched release)

Discovery Timeline

• 2026-03-30 - CVE-2026-33029 published to NVD
• 2026-04-02 - Last updated in NVD database

Technical Details for CVE-2026-33029

Vulnerability Analysis

This vulnerability stems from improper input validation (CWE-20) in the Nginx UI logrotate configuration functionality. The application fails to implement proper boundary checks on user-supplied input for the rotation interval parameter. When an authenticated user submits a negative integer value for this parameter, the backend logic enters an infinite loop or transitions to an invalid processing state.

The vulnerability requires network access and authenticated privileges to exploit, but does not require user interaction. Once triggered, the Denial of Service condition affects the availability of the web interface, preventing legitimate administrators from managing the Nginx server through the UI.

Root Cause

The root cause of CVE-2026-33029 is the absence of proper input validation and sanitization for numeric parameters in the logrotate configuration handler. The application accepts integer values without verifying they fall within acceptable bounds or are non-negative. When a negative value is processed, the backend logic cannot handle the unexpected input correctly, resulting in an infinite loop condition that exhausts server resources and renders the application unresponsive.

Attack Vector

The attack vector for this vulnerability is network-based and requires authenticated access to the Nginx UI application. An attacker with valid credentials can exploit this vulnerability through the following mechanism:

1. The attacker authenticates to the Nginx UI web interface with valid credentials
2. The attacker navigates to the logrotate configuration section
3. The attacker submits a maliciously crafted request containing a negative integer value for the rotation interval parameter
4. The backend processes the invalid input and enters an infinite loop
5. The web interface becomes unresponsive, denying service to all legitimate users

The vulnerability does not impact confidentiality or integrity, but has a high impact on availability as it completely disrupts the web interface functionality.

Detection Methods for CVE-2026-33029

Indicators of Compromise

• Sudden unresponsiveness of the Nginx UI web interface
• High CPU utilization on the server hosting Nginx UI without corresponding legitimate workload
• Unusual logrotate configuration change requests in application logs, particularly those containing negative values
• Backend process entering hung or zombie state

Detection Strategies

• Monitor application logs for configuration change requests containing negative or out-of-bounds values for rotation intervals
• Implement application performance monitoring to detect sudden resource exhaustion or hung processes
• Configure alerting for Nginx UI web interface availability and response time degradation
• Review access logs for repeated or automated configuration change attempts from authenticated users

Monitoring Recommendations

• Enable detailed logging for logrotate configuration changes in Nginx UI
• Set up health checks to monitor Nginx UI web interface responsiveness
• Implement CPU and memory usage alerts for the Nginx UI backend process
• Monitor authentication logs for suspicious access patterns or credential abuse

How to Mitigate CVE-2026-33029

Immediate Actions Required

• Upgrade Nginx UI to version 2.3.4 or later immediately
• Restrict access to Nginx UI to trusted administrative users only
• Implement network-level access controls to limit who can reach the Nginx UI web interface
• Review recent logrotate configuration changes for suspicious activity

Patch Information

The vulnerability has been patched in Nginx UI version 2.3.4. Organizations should upgrade to this version or later to remediate the vulnerability. The patch information and release details are available in the GitHub Release v2.3.4. Additional details about the security issue can be found in the GitHub Security Advisory GHSA-cp8r-8jvw-v3qg.

Workarounds

• Implement a web application firewall (WAF) rule to validate and reject requests containing negative values for rotation interval parameters
• Restrict authenticated access to the logrotate configuration functionality to only highly trusted administrators
• Deploy network segmentation to limit access to the Nginx UI management interface
• Consider temporarily disabling the logrotate configuration feature until the patch can be applied

# Example: Restrict access to Nginx UI at the network level using iptables
# Allow only trusted admin IP addresses to access Nginx UI (default port 9000)
iptables -A INPUT -p tcp --dport 9000 -s 10.0.0.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 9000 -j DROP