Related Vulnerabilities: CVE-2021-3618  

ALPACA is an application layer protocol content confusion attack, exploiting TLS servers implementing different protocols but using compatible certificates, such as multi-domain or wildcard certificates. A MiTM attacker having access to victim's traffic at the TCP/IP layer 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.

Severity Medium

Remote Yes

Type Insufficient validation

Description

ALPACA is an application layer protocol content confusion attack, exploiting TLS servers implementing different protocols but using compatible certificates, such as multi-domain or wildcard certificates.  A MiTM attacker having access to victim's traffic at the TCP/IP layer 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.

AVG-2102 nginx 1.20.1-1 Medium Vulnerable

AVG-2101 vsftpd 3.0.3-7 Medium Vulnerable

AVG-2103 nginx-mainline 1.19.10-1 1.21.0-1 Medium Fixed

https://bugzilla.redhat.com/show_bug.cgi?id=1975623
https://github.com/nginx/nginx/commit/173f16f736c10eae46cd15dd861b04b82d91a37a