cve/2021/CVE-2021-30639.md

### [CVE-2021-30639](https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-30639)
![](https://img.shields.io/static/v1?label=Product&message=Apache%20Tomcat&color=blue)
![](https://img.shields.io/static/v1?label=Version&message=Apache%20Tomcat%2010%2010.0.3%20to%2010.0.4%20&color=brightgreen)
![](https://img.shields.io/static/v1?label=Version&message=Apache%20Tomcat%208.5%208.5.64%20&color=brightgreen)
![](https://img.shields.io/static/v1?label=Version&message=Apache%20Tomcat%209%209.0.44%20&color=brightgreen)
![](https://img.shields.io/static/v1?label=Vulnerability&message=Denial%20of%20Service&color=brightgreen)

### Description

A vulnerability in Apache Tomcat allows an attacker to remotely trigger a denial of service. An error introduced as part of a change to improve error handling during non-blocking I/O meant that the error flag associated with the Request object was not reset between requests. This meant that once a non-blocking I/O error occurred, all future requests handled by that request object would fail. Users were able to trigger non-blocking I/O errors, e.g. by dropping a connection, thereby creating the possibility of triggering a DoS. Applications that do not use non-blocking I/O are not exposed to this vulnerability. This issue affects Apache Tomcat 10.0.3 to 10.0.4; 9.0.44; 8.5.64.

### POC

#### Reference
- https://kc.mcafee.com/corporate/index?page=content&id=SB10366
- https://www.oracle.com/security-alerts/cpujan2022.html

#### Github
- https://github.com/20142995/nuclei-templates
- https://github.com/cyb3r-w0lf/nuclei-template-collection