CVE-2021-37350

What it actually does

Nagios XI versions before 5.8.5 contain an SQL injection flaw in the Bulk Modifications Tool caused by insufficient sanitization of user-controlled input before it is used in database queries. A remote attacker can manipulate SQL syntax sent to the backend database, potentially reading sensitive data, modifying monitoring configuration, creating or altering application records, and in some cases causing service disruption. Because Nagios XI stores configuration, credentials, monitoring targets, and operational metadata, successful exploitation can expose information useful for broader compromise.

Why it matters to the business

Compromise of a Nagios XI server can undermine monitoring integrity, expose infrastructure details, and allow attackers to tamper with alerts or monitored assets. This may lead to missed outages or security events, disclosure of sensitive operational data, credential exposure, and disruption of monitoring services. The high CVSS score and high EPSS probability indicate this should be treated as an urgent internet-facing application risk even though it is not currently listed in the CISA Known Exploited Vulnerabilities catalog.

How an attack unfolds

An attacker identifies a Nagios XI instance running a vulnerable version prior to 5.8.5 and targets the Bulk Modifications Tool endpoint. By supplying crafted input containing SQL control characters or expressions, the attacker causes Nagios XI to execute unintended SQL statements against its backend database. Initial exploitation may be used to confirm injection behavior through database errors, timing delays, or changed responses. The attacker can then enumerate database structure, extract application data, alter monitoring configuration, create persistence through application-level changes, or degrade availability by issuing expensive or destructive database operations. If sensitive credentials or infrastructure details are retrieved, the attacker may use them to pivot to monitored systems or suppress monitoring while conducting further activity.

How to fix it

Upgrade Nagios XI to version 5.8.5 or later. If immediate upgrade is not possible, restrict access to the Nagios XI web interface and Bulk Modifications Tool to trusted administrative networks, require strong authentication and MFA where available, place the interface behind VPN or zero-trust access controls, and use a WAF rule to block obvious SQL injection payloads as a temporary compensating control. Review Nagios XI users, API keys, stored credentials, and monitoring configuration after remediation, especially if the instance was internet-accessible. Rotate any credentials stored in or accessible through Nagios XI if exploitation is suspected.

How to confirm the fix worked

Confirm the installed Nagios XI version is 5.8.5 or later from the web UI, package metadata, or server-side version files. Verify that vulnerable Bulk Modifications Tool code has been updated and that the Nagios XI interface is not broadly exposed to untrusted networks. Perform an authenticated or controlled vulnerability scan that specifically checks for CVE-2021-37350 or Nagios XI versions prior to 5.8.5. Review web server logs to confirm that requests to the Bulk Modifications Tool no longer produce SQL errors, timing anomalies, or abnormal response patterns when benign validation inputs are used.

Typical attack path

1. Discover an exposed Nagios XI web interface and determine that it is running a version earlier than 5.8.5.
2. Send crafted requests to the Bulk Modifications Tool with SQL metacharacters or database functions in vulnerable parameters.
3. Confirm exploitability through error messages, timing differences, response changes, or database behavior.
4. Enumerate database tables and extract Nagios XI data such as users, configuration, monitored hosts, service definitions, and stored secrets where accessible.
5. Modify monitoring configuration, user records, or alerting behavior to create persistence, hide activity, or disrupt operations.
6. Use exposed credentials or infrastructure knowledge to pivot to other systems or continue reconnaissance.

How to detect it

To determine whether exploitation already occurred, review web server access and error logs for requests to Nagios XI Bulk Modifications Tool endpoints containing SQL injection syntax, encoded quotes, UNION queries, time-delay functions, or references to database metadata. Relevant log sources commonly include Apache or HTTPD access/error logs, Nagios XI application logs, PHP error logs, database query/error logs, WAF logs, reverse proxy logs, EDR telemetry, and authentication logs. Look for anomalous requests to bulk modification components followed by SQL errors, unusually long response times, large response sizes, repeated parameter fuzzing, or access from unfamiliar IP addresses. Investigate any subsequent Nagios XI configuration changes, unexpected user or API key creation, altered notification commands, disabled checks, changed contact groups, or unexplained database writes. If database logging is available, search for suspicious use of information_schema, UNION SELECT, SLEEP, BENCHMARK, INTO OUTFILE, LOAD_FILE, or attempts to enumerate users and configuration tables around the time of suspicious web requests.

• /nagiosxi/includes/components/bulkmodifications/bulkmodifications.php
• bulkmodifications.php
• /nagiosxi/includes/components/bulkmodifications/
• /usr/local/nagiosxi/html/includes/components/bulkmodifications/
• UNION SELECT
• UNION%20SELECT
• information_schema
• SLEEP(
• BENCHMARK(
• LOAD_FILE(
• INTO OUTFILE
• %27%20OR%20%271%27%3D%271
• ' OR '1'='1
• OR 1=1
• SQL syntax
• mysql_fetch
• mysqli_fetch
• You have an error in your SQL syntax

What your security team should do

• Prioritize upgrading all Nagios XI deployments to 5.8.5 or later, especially internet-facing systems.
• Restrict Nagios XI administrative access to trusted networks, VPN, or identity-aware access gateways.
• Search historical web, application, and database logs for SQL injection attempts against Bulk Modifications Tool endpoints.
• Review Nagios XI user accounts, API keys, notification settings, monitored host definitions, and recent configuration changes for unauthorized modifications.
• Rotate credentials stored in Nagios XI or used by Nagios XI if exploitation cannot be ruled out.
• Add SIEM detections for SQL injection patterns in requests to Nagios XI endpoints, especially bulk modification components.
• Ensure database and web server logging are enabled with sufficient retention to support future investigation.