CVE-2021-3618 Other in ALPACA

What is CVE-2021-3618?

CVE-2021-3618 is a high-severity vulnerability in Debian Debian Linux, published on 23 Mar 2022. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official 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.

Weakness: CWE-295

Which versions are affected by CVE-2021-3618?

2 open source packages ship an affected version, including nginx and nginx-gateway. It affects 5 products.

Products include Debian Debian Linux, F5 Nginx, Fedoraproject Fedora, Sendmail Sendmail, Vsftpd Project Vsftpd.

How do I fix CVE-2021-3618?

Upgrade nginx to 1.21.0 or later.

Is CVE-2021-3618 being exploited?

There is no known exploitation of CVE-2021-3618 in the wild and no public exploit code.

Other vulnerabilities in Debian Debian Linux

• CVE-2015-3306 ProFTPD Improper Access Control Exploited Critical 10.0
• CVE-2025-49113 RoundCube Webmail Deserialization of Untrusted Data Exploited Critical 9.9
• CVE-2026-24061 GNU InetUtils Argument Injection Exploited Critical 9.8
• CVE-2025-39682 Linux Kernel Improper Check for Unusual or Exceptional Conditions Exploited Critical 9.8
• CVE-2024-9680 Mozilla Firefox Use-After-Free Exploited Critical 9.8

All Debian Debian Linux vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as ALPINE-CVE-2021-3618, AZL-9188, AZL-9190, AZL-9220, BIT-nginx-2021-3618, BIT-nginx-gateway-2021-3618 and 23 more.