cve/2021/CVE-2021-31618.md

### [CVE-2021-31618](https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-31618)
![](https://img.shields.io/static/v1?label=Product&message=Apache%20HTTP%20Server&color=blue)
![](https://img.shields.io/static/v1?label=Version&message=%3D%202.4.47%20&color=brighgreen)
![](https://img.shields.io/static/v1?label=Vulnerability&message=CWE-476%20NULL%20Pointer%20Dereference&color=brighgreen)

### Description

Apache HTTP Server protocol handler for the HTTP/2 protocol checks received request headers against the size limitations as configured for the server and used for the HTTP/1 protocol as well. On violation of these restrictions and HTTP response is sent to the client with a status code indicating why the request was rejected. This rejection response was not fully initialised in the HTTP/2 protocol handler if the offending header was the very first one received or appeared in a a footer. This led to a NULL pointer dereference on initialised memory, crashing reliably the child process. Since such a triggering HTTP/2 request is easy to craft and submit, this can be exploited to DoS the server. This issue affected mod_http2 1.15.17 and Apache HTTP Server version 2.4.47 only. Apache HTTP Server 2.4.47 was never released.

### POC

#### Reference
- https://www.oracle.com/security-alerts/cpuoct2021.html

#### Github
- https://github.com/ARPSyndicate/cvemon