CVE-2023-24034: Nagios XI Open Redirect Vulnerability

CVE-2023-24034 Overview

CVE-2023-24034 is an open redirect vulnerability in twilio_ajax_handler.php in Nagios XI before version 5.9.3. An attacker can craft a malicious URL that leverages the vulnerable handler to redirect an authenticated Nagios XI user to an attacker-controlled site. The flaw is classified under CWE-601: URL Redirection to Untrusted Site. Exploitation requires user interaction, typically through a phishing link, and enables credential harvesting or malware delivery campaigns that abuse the trust users place in the Nagios XI domain.

Critical Impact
Attackers can weaponize the trusted Nagios XI hostname to redirect authenticated administrators to malicious sites, enabling phishing and social engineering attacks against monitoring platform users.

Affected Products

Nagios XI versions prior to 5.9.3
The vulnerable component is twilio_ajax_handler.php
Fixed in Nagios XI 5.9.3 and later

Discovery Timeline

2026-09-14 - CVE-2023-24034 published to NVD
2026-09-14 - Last updated in NVD database

Technical Details for CVE-2023-24034

Vulnerability Analysis

The vulnerability resides in the twilio_ajax_handler.php script, which processes AJAX requests related to Twilio integration within Nagios XI. The handler accepts a user-controllable URL parameter and issues an HTTP redirect without validating that the destination belongs to a trusted domain or matches an allowlist.

An attacker crafts a URL pointing to the vulnerable endpoint on a legitimate Nagios XI installation. The URL contains a redirect target under attacker control. When a victim clicks the link, the Nagios XI server responds with a redirect that sends the browser to the attacker's site while the address bar initially shows the trusted host.

This behavior facilitates phishing pages that mimic Nagios XI or corporate single sign-on portals. Attackers also chain open redirects with OAuth flows and password reset workflows to bypass referrer-based protections.

Root Cause

The root cause is missing validation of a redirect destination parameter in twilio_ajax_handler.php. The code passes a user-supplied value directly into a redirect response without enforcing a host allowlist, relative-path constraint, or signed token. This maps to CWE-601.

Attack Vector

Exploitation occurs over the network and requires user interaction. The attacker distributes a crafted link, typically through email, chat, or social media. The victim's browser makes the request to the Nagios XI host, and the server returns a redirect to the attacker-controlled URL. No authentication bypass or code execution occurs on the Nagios XI server itself; the impact is limited to abuse of the trusted origin.

See the Nagios Security Disclosures page for vendor advisory details.

Detection Methods for CVE-2023-24034

Indicators of Compromise

Web server access logs showing requests to twilio_ajax_handler.php with URL, redirect, or similar query parameters containing external hostnames
HTTP 3xx responses from the Nagios XI server with Location headers pointing to domains outside the organization
Phishing reports from users mentioning links that initially resolved to the Nagios XI hostname

Detection Strategies

Parse Nagios XI web logs for requests to twilio_ajax_handler.php where query parameters contain fully qualified URLs or encoded protocol schemes such as http%3A%2F%2F
Correlate outbound redirects from monitoring infrastructure with newly registered or low-reputation domains using threat intelligence enrichment
Alert on user-agent patterns typical of email link scanners followed by real browser traffic hitting the same redirect endpoint

Monitoring Recommendations

Enable verbose access logging on the Nagios XI web tier and forward events to a central log platform for retention and search
Monitor for phishing infrastructure that references the Nagios XI hostname in URL paths or subdomains
Track version and patch state of Nagios XI instances to confirm the fix is deployed across all monitored environments

How to Mitigate CVE-2023-24034

Immediate Actions Required

Upgrade Nagios XI to version 5.9.3 or later as documented in the Nagios XI Change Log
Inventory all Nagios XI deployments, including staging and disaster recovery environments, to ensure consistent patch coverage
Notify Nagios XI users about phishing risk and reinforce guidance to inspect final destination URLs after clicking monitoring links

Patch Information

Nagios released a fix in Nagios XI 5.9.3. Administrators should follow the vendor upgrade procedure and confirm the version after installation. Consult the Nagios XI Change Log for release notes and the Nagios Security Disclosures page for the associated advisory.

Workarounds

Restrict network access to the Nagios XI web interface through firewall rules or VPN so external users cannot reach twilio_ajax_handler.php
Deploy a reverse proxy or web application firewall rule that blocks requests to twilio_ajax_handler.php containing absolute URLs in query parameters
Disable Twilio integration if it is not used, reducing exposure of the vulnerable handler

bash

# Example web application firewall rule blocking external redirect targets
# Adapt the pattern to your WAF syntax
SecRule REQUEST_URI "@contains twilio_ajax_handler.php" \
  "chain,deny,status:403,id:1024034,msg:'CVE-2023-24034 open redirect attempt'"
SecRule ARGS "@rx ^(https?:)?//" "t:none,t:urlDecodeUni"