Arch Linux 2021-06-23 Alert: Critical Apache DoS Security Vulnerability

Arch Linux Security Advisory ASA-202106-23
=========================================
Severity: High
Date    : 2021-06-09
CVE-ID  : CVE-2021-31618
Package : apache
Type    : denial of service
Remote  : Yes
Link    : https://security.archlinux.org/AVG-2041

Summary
======
The package apache before version 2.4.48-1 is vulnerable to denial of
service.

Resolution
=========
Upgrade to 2.4.48-1.

# pacman -Syu "apache>=2.4.48-1"

The problem has been fixed upstream in version 2.4.48.

Workaround
=========
None.

Description
==========
A security issue has been found in the Apache HTTP Server (httpd)
before version 2.4.48. The 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, an 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 footer. This led to a NULL pointer
dereference on initialised memory, reliably crashing the child process.
Since such a triggering HTTP/2 request is easy to craft and submit,
this can be exploited for denial of service (DoS) of the server.

Impact
=====
A remote attacker could crash the HTTP server using a crafted HTTP/2
request.

References
=========
https://httpd.apache.org/security/vulnerabilities_24.html#CVE-2021-31618

https://security.archlinux.org/CVE-2021-31618