Rewterz Threat Advisory – CVE-2018-11763 – Apache HTTP Server SETTINGS Frames Denial of Service Vulnerability

A vulnerability has been reported in Apache HTTP Server, which can be exploited by malicious people to cause a DoS (Denial of Service).

IMPACT:  NORMAL

PUBLISH DATE: 26-09-2018

OVERVIEW

In Apache HTTP Server 2.4.17 to 2.4.34, an attacker could induce a Denial of Service by sending continuous SETTINGS frames of maximum size on an ongoing HTTP/2 connection. It will keep the connection busy and will prevent it from timing out. This can be abused for a DoS on the server. Only servers that have enabled the h2 protocol can be affected.

ANALYSIS

A vulnerability is found in some versions of the Apache HTTP Server that may lead to a Denial of Service condition. This error affects an unknown function of the component SETTINGS Frame Handler.

When handling SETTINGS frames of maximum size an ongoing HTTP/2 connection can be exploited. The connection won’t time out, and may cause Denial of Service. It impacts the availability of an organization.

However, successful exploitation of this error requires that h2 protocol is enabled in the server. This network vulnerability does not require any privileges or user interaction to be exploited.

AFFECTED PRODUCTS

Apache HTTP Server 2.4.x

(The vulnerability is reported in versions 2.4.34, 2.4.33, 2.4.30, 2.4.29, 2.4.28, 2.4.27, 2.4.26, 2.4.25, 2.4.23, 2.4.20, and 2.4.18.)

(The httpd packages in Red Hat Enterprise Linux 7 and earlier do not include support for HTTP/2 and hence are not affected by this issue.)

UPDATES

Update to version 2.4.35. Refer to links for further help.

http://httpd.apache.org/download.cgi

https://websiteforstudents.com/apache2-http-server-2-4-35-released-heres-how-to-install-upgrade-on-ubuntu-16-04-18-04-lts/

MITIGATION

Apart from updating to the patched version, another possible mitigation is to not enable the h2 protocol.

If you think you are a victim of a cyberattack, immediately send an email to info@rewterz.com.