HTTP request suggling in HAProxy

1) Inconsistent interpretation of HTTP requests

EUVDB-ID: #VU56401

Risk: Medium

CVSSv3.1: 6.5 [CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N/E:P/RL:O/RC:C]

CVE-ID: CVE-2021-40346

CWE-ID: CWE-444 - Inconsistent Interpretation of HTTP Requests ('HTTP Request Smuggling')

Exploit availability: Yes

Description

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

The vulnerability exists due to improper validation of HTTP/2 requests within the htx_add_header() and htx_add_trailer() functions when processing HTTP header name length encoding in the HTX representation. A remote attacker can send a specially crafted HTTP request to the server and smuggle HTTP headers.

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

Mitigation

Install update from vendor's website.

Vulnerable software versions

HAProxy: 2.0.0 - 2.4.3

External links

http://www.mail-archive.com/haproxy@formilux.org/msg41114.html
http://git.haproxy.org/?p=haproxy.git;a=commit;h=3b69886f7dcc3cfb3d166309018e6cfec9ce2c95

Q & A

Can this vulnerability be exploited remotely?

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

How the attacker can exploit this vulnerability?

The attacker would have to send a specially crafted request to the affected application in order to exploit this vulnerability.

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.