Vulnerability identifier: #VU56474

Vulnerability risk: Medium

CVSSv3.1: 6.3 [CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N/E:U/RL:O/RC:C]

CVE-ID: CVE-2021-33193

CWE-ID: CWE-444

Exploitation vector: Network

Exploit availability: No

Vulnerable software:
Apache HTTP Server
Server applications / Web servers

Vendor: Apache Foundation

Description

The vulnerability allows a remote attacker to preform HTTP/2 request smuggling attacks.

The vulnerability exists due to improper validation of HTTP/2 requests in mod_proxy in Apache HTTP Server. A remote attacker can send a specially crafted HTTP/2 request to the server and smuggle arbitrary HTTP headers.

Successful exploitation of vulnerability may allow an attacker to poison web server cache and perform phishing attacks.

Mitigation
Install update from vendor's website.

Vulnerable software versions

Apache HTTP Server: 2.4.17 - 2.4.48

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External links
http://portswigger.net/research/http2
http://github.com/apache/httpd/commit/ecebcc035ccd8d0e2984fe41420d9e944f456b3c.patch
http://downloads.apache.org/httpd/CHANGES_2.4

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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.