OWASP Top-10 2021. Statistics-based proposal.

OWASP Top 10 Security Risks and Vulnerabilities

Everybody knows the OWASP Top-10 as well as the fact that it gets updated only every other 3-4 years. With the last update published in 2017, it’s no surprise that a new version is coming this year. During my application security career, I saw OWASP Top-10 at least in 2003, 2004, 2007, 2010, 2013, and 2017. 

Since the OWASP creation process is not documented well, it seems reasonable to build an open and transparent rating for the same categories based on a large number of security reports.

The purpose of this work is to make an OWASP Top-10 2021 predictions calculated by understandable metrics, make everyone able to reproduce the results, and present to an entire community for the feedback. The following work is based on an analysis of 2 million of security reports from 144 public sources including CVE bulletins, bug bounty reports, and vendor security bulletins. 

Categories overlaps in OWASP Top-10 

The first thing that I should mention about OWASP Top-10 is that it’s not a vulnerability classification and not even the classification at any point, since categories overlap. I am referring to the security boulevard article and our blog post that describes the interference presented at the following diagram:

OWASP Top 10 2017 categories overlaps

To sum up: OWASP Top-10 IS NOT a vulnerability classification, but rather the list of the risks that have been revealed during the last period of time. That’s why to predict the next OWASP Top-10 2021 list, we have to analyze threats to the targeted web assets for the last four years. So, here we go.


To find the statistical data, we used the Vulners.com which is an aggregated database that includes more than 4 million bulletins from 144 vendors, including bug bounty programs like HackerOne. 

The total amount of bulletins used to build this list is 2 168 521 (search query: "published:[2018-01-01 TO 2020-12-31]"). 

To split data by the categories, we built vulners search queries for all the ten OWASP categories. Even though the full-text search is not the most accurate solution to classify data, I think I can rely on this particular task. The point is that all the OWASP categories could be found in security bulletins by searching for acronyms and abbreviations like XSS, XXE, SQL, RCE, etc. 

The category “Known Vulnerabilities” is out of the full-text search query. The total number of web-related security reports were taken as a total amount of CVE numbers assigned for the last three years.

It’s not a joke, but according to the Vulners statistics, XSS takes 20% of ALL the security bulletins for the last three years. It’s almost 10x more than all the CVEs issued in the last three years. Since many of XSS doesn’t have a CVSS score (meaning zero), an average score for that many of them is still 0.1. That fact, however, doesn't stop XSS from hitting the Top-3 in a chart. Again, because it’s as many of them as each fifth bulletin was found in the last three years.

You can reuse the following queries to validate, modify, or make your own analysis:

Top-10 2017 to 2021 mappingSearch query
A1. Injectionsinjection OR traversal OR lfi OR "os command" OR SSTI OR RCE OR "remote code"
A2. Broken authauthentication
A3. Sensitive data exposuresensitive AND data
MERGE: A8. Insecure Deserialization + A4. XXEXXE OR deserialize OR deserialization OR "external entities"
A5. Broken Access Controlaccess control
A6. Security Misconfigurationmisconfiguration OR misconfigure OR misconfig
NEW: SSRFSSRF OR "server side request forgery"
A9. Known Vulnerabilitiestype:cve and (http OR web OR html)
A10. Insufficient Logging & Monitoringlogging
OWASP Top Ten 2021 vulners search queries

As you can see, my strong opinion is that the OWASP community will add the new category SSRF and merge “A4. XXE - XML External Entity” and “A8. Insecure Deserialization” in the upcoming OWASP Top-10 2021. Here is why. 

Proposal 1. Add SSRF as a new category.

As an SSRF inventor and author of the “SSRF bible cheatsheet”, I definitely keep warm feelings about it. 

In spite of this, please allow me to mention just the four most powerful facts related to SSRF:

  1. The SSRF attacks become #3 of the most critical vulnerabilities as of H1 2020 stats https://www.hackerone.com/top-ten-vulnerabilities
  2. Amazon took it seriously and patched in for EC2 meta-data services at the end of 2019: https://aws.amazon.com/blogs/security/defense-in-depth-open-firewalls-reverse-proxies-ssrf-vulnerabilities-ec2-instance-metadata-service/
  3. SSRF caused a lot of high-risk security problems, including the most famous Capital One hack with a WAF bypass, explained in details by Krebs on Security https://krebsonsecurity.com/2019/08/what-we-can-learn-from-the-capital-one-hack/ 
  4. According to the global stats collected by Vulners, SSRF mentioned in 912 bulletins last three years, almost the same amount of times as OWASP Top-10 2017 A4 / XXE (1000 results) and 2.5x more often than security misconfiguration (A6 / 481 results). 

To sum up, SSRF is a critical issue that causes cloud takeovers, remote code execution, data breaches, and other information security risks. It’s impossible to fix SSRF by input filtration and other data validation mechanisms. Amazon and other cloud providers take it seriously and apply changes to their infrastructures to mitigate these threats. SSRF issues mentioned in almost the same amount of security bulletins as XXE in the last three years. That’s why I’m sure nobody will blame me for adding it to the OWASP Top-10 2021.

Proposal 2. Merge XXE and Insecure Deserialization

XML is the serialization format, according to Wikipedia (https://en.wikipedia.org/wiki/Serialization). The XXE vulnerability, a.k.a. Xml eXternal Entities is technically a serialization feature that allows to include local and remote files content into the XML document. Sometimes it causes SSRF, by the way. That’s why it's absolutely true that XXE is a part of Insecure Deserialization category anyways, which I mentioned in a bunch of articles related to the OWASP Top 10 2017 weaknesses. 

Also, there is no way to claim XXE as the separate category if gathering pretty much everything from SQL injection to Path Traversal and OS commanding a vague group “A1. Injections” which will lead OWASP for years, for sure. 

Because of these two facts, plus based on a statistical data of the amount of security reports in each of the categories, I decided to merge XXE and Insecure Deserialization to a single class. 

Proposal 3. Introduce Overall Risk Score

To sort my assumptions of the OWASP Top-10, for each of the categories, I applied an average CVSS score multiplies to the amount of reports. In fact, because a lot of the bulletins have 0 CVSS score, the result rating should be interpreted as an average CVSS score for the category, but just demonstrates the right proportions between them. 

In a few words, to sort OWASP categories, the following formula was applied:

Overall Risk = Avg. CVSS x Amount of Bulletins

Calculating the OWASP Top 10 2021 rating

As mentioned above, I used an aggregated data from 144 data sources such as security bulletins that Vulners.com indexed. This approach allows to count not only CVE data but all the reports, including bug bounties, exploits, and scanner detects that rely on the real state of information security. If we will count only CVEs, the results will be dramatically different, since the category “Known vulnerabilities” will be technically equal in a count to all the other categories in a sum. 

So, here is the fairest way of building OWASP Top-10, look at that!

#OWASPTop-10 2021Vulners search queryAvg. CVSS# of bulletinsOverall score
A1Injectionsinjection OR traversal OR lfi OR "os command" OR SSTI OR RCE OR "remote code"4.8334061164514.63
A2Broken Authenticationauthentication4.081373556038.8
A3Cross-Site Scripting (XSS)xss0.143335343335.3
A4Sensitive Data Exposuresensitive AND data3.55599021264.5
A5Insecure DeserializationXXE OR deserialize OR deserialization OR "external entities"5.33298515910.05
A6Broken Access Controlaccess control0.721696712216.24
A7Insufficient Logging & Monitoringlogging3.3523097735.15
A8Server Side Request Forgery (SSRF)SSRF OR "server side request forgery"3.811394328.2
A9Known Vulnerabilitiestype:cve and (http OR web OR html)5.383762022.88
A10Security Misconfigurationmisconfiguration OR misconfigure OR misconfig2.274801089.6
OWASP Top Ten 2021 categories statistical data

Results and OWASP Top Ten 2017 comparison

After all, I’m pretty confident to share the following proposal of OWASP Top 10 for 2021, since it’s based on statistical data available publicly.

OWASP Top Ten 2021 proposal
OWASP Top Ten 2021 proposal

I hope these data will be useful for risk assessments, vulnerability management, education purposes, and just interesting reading for application security experts and enthusiasts. 

Application security experts could also find interesting distribution these categories by amount of security reports, mean bulletins, bug bounties, exploits, altogether:

Thanks for reading! Ivan, Wallarm.

Special thanks to Vulners.com team for helping with data collection and analysis.

Frequently Asked Questions

What is OWASP Top-10 2021?
OWASP Top-10 2021 is a list of the most critical security risks to web applications identified by the Open Web Application Security Project. It helps organizations prioritize security risks and improve their application security posture.

What are the OWASP Top-10 2021 categories?
The OWASP Top-10 2021 categories include: injection, broken authentication and session management, sensitive data exposure, XML external entities (XXE), broken access control, security misconfigurations, cross-site scripting (XSS), insecure deserialization, insufficient logging and monitoring, and server-side request forgery (SSRF).

Why is the OWASP Top-10 2021 important?
The OWASP Top-10 2021 provides a roadmap for organizations to focus on the most important security risks facing web applications. By addressing these risks, organizations can reduce the likelihood of successful attacks and protect their assets, reputation, and customers.

How can I use the OWASP Top-10 2021 in my organization?
You can use the OWASP Top-10 2021 as a guide for identifying and mitigating security risks in your web applications. It is recommended to perform regular security assessments and use secure coding practices to reduce the likelihood of vulnerabilities.

More information on OWASP Top-10 2021:
Here's a link to the official OWASP Top-10 2021 website: https://owasp.org/Top10/


API security Tutorial

OWASP ZAP - Zed Attack Proxy