CVE-2021-31618 : Security Advisory and Response

Apache HTTP Server protocol handler for the HTTP/2 protocol had a vulnerability that allowed a NULL pointer dereference when processing specific HTTP/2 requests. Attackers could exploit this to cause a denial of service (DoS) by crashing the server.

Understanding CVE-2021-31618

This CVE identifies a critical vulnerability in Apache HTTP Server related to handling HTTP/2 requests.

What is CVE-2021-31618?

The vulnerability in the HTTP/2 protocol handler of Apache HTTP Server could lead to a NULL pointer dereference, resulting in a server crash when processing certain requests.

The Impact of CVE-2021-31618

This vulnerability could be exploited by malicious actors to craft and submit specially designed HTTP/2 requests that could cause a DoS condition by crashing the server child process.

Technical Details of CVE-2021-31618

The vulnerability arises due to uninitialized memory in the HTTP/2 protocol handler, specifically triggered when an offending header is the first one received or appears in a footer. The issue affects mod_http2 1.15.17 and Apache HTTP Server version 2.4.47.

Vulnerability Description

The flaw leads to a NULL pointer dereference, resulting in a predictable server crash on processing specific HTTP/2 requests.

Affected Systems and Versions

The vulnerability affects mod_http2 1.15.17 and Apache HTTP Server version 2.4.47.

Exploitation Mechanism

By crafting and submitting a triggering HTTP/2 request, attackers can exploit the uninitialized memory to crash the server and achieve a DoS condition.

Mitigation and Prevention

To mitigate this vulnerability, unpatched servers can disable the

h2

protocol by removing it from the

Protocols

configuration. If the

h2

protocol is not enabled, the server is not affected.

Immediate Steps to Take

Disable the

h2

protocol on unpatched servers.

Long-Term Security Practices

Regularly update and patch Apache HTTP Server to the latest version to address known vulnerabilities.

Patching and Updates

Refer to the official Apache HTTP Server website for security advisories and patch releases.