Denial of service when handling HTTP/2 requests in Apache HTTP server

Published: 2016-12-06 | Updated: 2016-12-21
Risk Low
Patch available YES
Number of vulnerabilities 1
CVE-ID CVE-2016-8740
Exploitation vector Network
Public exploit Public exploit code for vulnerability #1 is available.
Vulnerable software
Apache HTTP Server
Server applications / Web servers

Vendor Apache Foundation

Security Bulletin

This security bulletin contains one low risk vulnerability.

1) Memory leak


Risk: Low


CVE-ID: CVE-2016-8740

CWE-ID: CWE-401 - Improper Release of Memory Before Removing Last Reference ('Memory Leak')

Exploit availability: Yes


The vulnerability allows a remote attacker to cause denial of service.

The vulnerability exists due to improper handling of HTTP/2 headers, when the Protocols configuration includes h2 or h2c. A remote attacker can send a specially crafted HTTP/2 request, containign CONTINUATION frames to vulnerable instance and consume all available memory resources.

Successful exploitation of the vulnerability will result in denial of service (DoS) of affected web server.


On December 20 vendor has issued a new version of Apache HTTP Server 2.4.25 to address this vulnerability.

As a temporary solution it is recommended to limit access to HTTP/2 protocol to trusted IPs only.

Vulnerable software versions

Apache HTTP Server: 2.4.17 - 2.4.23

CPE2.3 External links

Q & A

Can this vulnerability be exploited remotely?

How the attacker can exploit this vulnerability?

Is there known malware, which exploits this vulnerability?