Skip to content

A09:2021 – Security Logging and Monitoring Failures icon


CWEs Mapped Max Incidence Rate Avg Incidence Rate Avg Weighted Exploit Avg Weighted Impact Max Coverage Avg Coverage Total Occurrences Total CVEs
4 19.23% 6.51% 6.87 4.99 53.67% 39.97% 53,615 242


Security logging and monitoring came from the Top 10 community survey (#3), up slightly from the tenth position in the OWASP Top 10 2017. Logging and monitoring can be challenging to test, often involving interviews or asking if attacks were detected during a penetration test. There isn't much CVE/CVSS data for this category, but detecting and responding to breaches is critical. Still, it can be very impactful for accountability, visibility, incident alerting, and forensics. This category expands beyond CWE-778 Insufficient Logging to include CWE-117 Improper Output Neutralization for Logs, CWE-223 Omission of Security-relevant Information, and CWE-532 Insertion of Sensitive Information into Log File.


Returning to the OWASP Top 10 2021, this category is to help detect, escalate, and respond to active breaches. Without logging and monitoring, breaches cannot be detected. Insufficient logging, detection, monitoring, and active response occurs any time:

  • Auditable events, such as logins, failed logins, and high-value transactions, are not logged.

  • Warnings and errors generate no, inadequate, or unclear log messages.

  • Logs of applications and APIs are not monitored for suspicious activity.

  • Logs are only stored locally.

  • Appropriate alerting thresholds and response escalation processes are not in place or effective.

  • Penetration testing and scans by dynamic application security testing (DAST) tools (such as OWASP ZAP) do not trigger alerts.

  • The application cannot detect, escalate, or alert for active attacks in real-time or near real-time.

You are vulnerable to information leakage by making logging and alerting events visible to a user or an attacker (see A01:2021-Broken Access Control).

How to Prevent

Developers should implement some or all the following controls, depending on the risk of the application:

  • Ensure all login, access control, and server-side input validation failures can be logged with sufficient user context to identify suspicious or malicious accounts and held for enough time to allow delayed forensic analysis.

  • Ensure that logs are generated in a format that log management solutions can easily consume.

  • Ensure log data is encoded correctly to prevent injections or attacks on the logging or monitoring systems.

  • Ensure high-value transactions have an audit trail with integrity controls to prevent tampering or deletion, such as append-only database tables or similar.

  • DevSecOps teams should establish effective monitoring and alerting such that suspicious activities are detected and responded to quickly.

  • Establish or adopt an incident response and recovery plan, such as National Institute of Standards and Technology (NIST) 800-61r2 or later.

There are commercial and open-source application protection frameworks such as the OWASP ModSecurity Core Rule Set, and open-source log correlation software, such as the Elasticsearch, Logstash, Kibana (ELK) stack, that feature custom dashboards and alerting.

Example Attack Scenarios

Scenario #1: A children's health plan provider's website operator couldn't detect a breach due to a lack of monitoring and logging. An external party informed the health plan provider that an attacker had accessed and modified thousands of sensitive health records of more than 3.5 million children. A post-incident review found that the website developers had not addressed significant vulnerabilities. As there was no logging or monitoring of the system, the data breach could have been in progress since 2013, a period of more than seven years.

Scenario #2: A major Indian airline had a data breach involving more than ten years' worth of personal data of millions of passengers, including passport and credit card data. The data breach occurred at a third-party cloud hosting provider, who notified the airline of the breach after some time.

Scenario #3: A major European airline suffered a GDPR reportable breach. The breach was reportedly caused by payment application security vulnerabilities exploited by attackers, who harvested more than 400,000 customer payment records. The airline was fined 20 million pounds as a result by the privacy regulator.


List of Mapped CWEs

CWE-117 Improper Output Neutralization for Logs

CWE-223 Omission of Security-relevant Information

CWE-532 Insertion of Sensitive Information into Log File

CWE-778 Insufficient Logging