CVE-2025-13826 Overview
CVE-2025-13826 is an Improper Input Validation vulnerability affecting Zervit's portable HTTP/web server. The vulnerability allows remote attackers to cause a Denial of Service (DoS) condition by sending malicious configuration reset requests. Due to inadequate validation of user-supplied input, an attacker can exploit this flaw to make the application stop responding, effectively disrupting service availability.
Critical Impact
Remote attackers can exploit this vulnerability to cause a complete service outage of the Zervit web server without authentication, impacting all users relying on the affected server instance.
Affected Products
- Zervit Portable HTTP/Web Server
Discovery Timeline
- 2026-04-21 - CVE-2025-13826 published to NVD
- 2026-04-21 - Last updated in NVD database
Technical Details for CVE-2025-13826
Vulnerability Analysis
This vulnerability stems from improper input validation (CWE-20) within Zervit's portable HTTP/web server. The application fails to adequately sanitize or validate user-supplied input when processing configuration reset requests. This weakness allows an attacker to craft malicious requests that trigger unexpected behavior in the server, ultimately causing it to become unresponsive.
The vulnerability is exploitable remotely over the network without requiring any prior authentication or user interaction, making it particularly dangerous for exposed Zervit instances. While the vulnerability does not impact confidentiality or integrity, the availability impact is significant as it can render the web server completely non-functional until a manual restart is performed.
Root Cause
The root cause of CVE-2025-13826 is the lack of proper input validation mechanisms when handling configuration reset requests. The Zervit portable HTTP/web server does not implement sufficient boundary checks or input sanitization routines for specific request parameters. When malformed or unexpected data is submitted through the configuration reset functionality, the application enters an error state that prevents it from processing further requests.
Attack Vector
The attack is network-based and can be executed remotely by any attacker who can reach the Zervit web server. The exploitation flow involves:
- Reconnaissance: Attacker identifies a target running Zervit portable HTTP/web server
- Request Crafting: Attacker creates a malicious HTTP request targeting the configuration reset functionality with specially crafted input
- Payload Delivery: The malicious request is sent to the vulnerable server
- Denial of Service: The server fails to properly handle the malicious input and stops responding to all subsequent requests
- Recovery: Manual restart of the application is required to restore service
The vulnerability mechanism involves sending malformed configuration reset requests that bypass input validation. When the server attempts to process these requests, it encounters an error condition that causes the application to hang or crash. For detailed technical information, refer to the INCIBE Security Notice.
Detection Methods for CVE-2025-13826
Indicators of Compromise
- Unusual volume of HTTP requests targeting configuration endpoints
- Server unresponsiveness following specific HTTP request patterns
- Multiple consecutive service restart events in application logs
- Malformed or anomalous configuration reset requests in access logs
Detection Strategies
- Monitor HTTP access logs for requests to configuration reset endpoints with unusual parameters or payload sizes
- Implement network intrusion detection rules to identify patterns associated with DoS attack attempts against web servers
- Configure application performance monitoring to alert on sudden service unavailability
- Deploy web application firewalls (WAF) to inspect and filter potentially malicious requests before they reach the server
Monitoring Recommendations
- Enable verbose logging on Zervit web server instances to capture detailed request information
- Set up automated alerting for service availability drops or unexpected restarts
- Monitor network traffic patterns for anomalies targeting Zervit server ports
- Implement real-time dashboards to track server response times and availability metrics
How to Mitigate CVE-2025-13826
Immediate Actions Required
- Restrict network access to Zervit web server instances to trusted IP ranges only
- Place the Zervit web server behind a reverse proxy or WAF that can filter malicious requests
- Implement rate limiting on configuration-related endpoints to prevent request flooding
- Monitor for service availability and configure automatic restart mechanisms as a temporary measure
Patch Information
No vendor patch information is currently available in the CVE data. Organizations should monitor the INCIBE Security Notice for updates on patches and vendor recommendations. Consider evaluating alternative web server solutions if patches are not forthcoming.
Workarounds
- Deploy a web application firewall (WAF) in front of the Zervit server to filter potentially malicious requests before they reach the application
- Implement strict firewall rules to limit access to the web server to only necessary IP addresses and networks
- Configure a reverse proxy to handle incoming requests and add an additional layer of input validation
- Set up automated monitoring and restart scripts to minimize downtime in the event of a successful attack
# Example: Restrict access using iptables (Linux)
# Allow only trusted IP ranges to access the web server port
iptables -A INPUT -p tcp --dport 80 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP
# Example: Configure automatic restart monitoring (systemd)
# Create a systemd service with automatic restart capability
# [Service]
# Restart=always
# RestartSec=5
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
