Vulnerability identifier: #VU1209

Vulnerability risk: Low

CVSSv3.1: 6.7 [CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H/E:P/RL:O/RC:C]

CVE-ID: CVE-2016-8740

CWE-ID: CWE-401

Exploitation vector: Network

Exploit availability: Yes

Vulnerable software:
Apache HTTP Server
Server applications / Web servers

Vendor: Apache Foundation

Description

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.

Mitigation
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

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External links
http://seclists.org/fulldisclosure/2016/Dec/17
http://httpd.apache.org/security/vulnerabilities_24.html

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Q & A

Can this vulnerability be exploited remotely?

Yes. This vulnerability can be exploited by a remote non-authenticated attacker via the Internet.

Is there known malware, which exploits this vulnerability?

No. We are not aware of malware exploiting this vulnerability. However, proof of concept for this vulnerability is available.