Security restrictions bypass in nginx

1) Origin validation error

EUVDB-ID: #VU59319

Risk: Medium

CVSSv3.1: 6.4 [CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N/E:U/RL:O/RC:C]

CVE-ID: CVE-2021-3618

CWE-ID: CWE-346 - Origin Validation Error

Exploit availability: No

Description

The vulnerability allows a remote attacker to bypass implemented security restrictions.

The vulnerability exists due to a logic error in TLS implementation when handling different protocols but using compatible certificates, such as multi-domain or wildcard certificates. A remote attacker with ability to perform TCP/IP layer MitM attack can redirect traffic from one subdomain to another, resulting in a valid TLS session. This breaks the authentication of TLS and cross-protocol attacks may be possible where the behavior of one protocol service may compromise the other at the application layer.

This attack technique was dubbed ALPACA (application layer protocol content confusion attack).

Mitigation

Install updates from vendor's website.

Vulnerable software versions

nginx: 1.0.0 - 1.20.0

External links

http://alpaca-attack.com/
http://bugzilla.redhat.com/show_bug.cgi?id=1975623
http://hg.nginx.org/nginx/rev/ec1071830799

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.