{"cve":"CVE-2021-3618","nvd":{"published":"2022-03-23T20:15:09.833","modified":"2026-06-17T04:05:27.083","status":"Modified","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.","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N","score":7.4},"cwes":["CWE-295"],"references":["https://alpaca-attack.com/","https://bugzilla.redhat.com/show_bug.cgi?id=1975623","https://lists.debian.org/debian-lts-announce/2022/11/msg00031.html","https://alpaca-attack.com/","https://bugzilla.redhat.com/show_bug.cgi?id=1975623"],"products":["debian:debian_linux","f5:nginx","fedoraproject:fedora","sendmail:sendmail","vsftpd_project:vsftpd"],"source":"nvd","synced_at":"2026-10-19T21:29:06.454770966+00:00"},"epss":{"cve":"CVE-2021-3618","score":0.02027,"percentile":0.81015,"date":"2026-10-31"},"kev":null,"osv":[],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}