CVE-2021-3618
Last modified
CVE-2021-3618 is a high-severity vulnerability rated 7.4/10 on the CVSS scale. 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. EPSS estimates a 2.04% chance of exploitation in the next 30 days.
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.
Metrics
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
Weakness Enumeration
Affected Software
| Vendor | Product | Versions |
|---|---|---|
| F5 | Nginx | < 1.21.0 |
| Sendmail | Sendmail | < 8.17 |
| Vsftpd Project | Vsftpd | < 3.0.4 |
| Fedoraproject | Fedora | 33 |
| Fedoraproject | Fedora | 34 |
| Fedoraproject | Fedora | 35 |
| Debian | Debian Linux | 10.0 |
References
- https://alpaca-attack.com/Third Party Advisory
- https://bugzilla.redhat.com/show_bug.cgi?id=1975623Issue Tracking, Patch, Third Party Advisory
- https://lists.debian.org/debian-lts-announce/2022/11/msg00031.htmlMailing List, Third Party Advisory
- https://alpaca-attack.com/Third Party Advisory
- https://bugzilla.redhat.com/show_bug.cgi?id=1975623Issue Tracking, Patch, Third Party Advisory
- https://lists.debian.org/debian-lts-announce/2022/11/msg00031.htmlMailing List, Third Party Advisory
Timeline
- Published
- Last Modified
- Status
- Modified
Frequently Asked Questions
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How Strix Helps
- How Strix found a critical auth bypass in etcdStrix autonomously discovered a critical authentication bypass in etcd, later designated CVE-2026-33413.
- Autonomous PentestingAI agents that find and validate exploitable vulnerabilities like this one across your applications.
- PR ReviewsPentest every pull request so vulnerable code is caught before it ships to production.
- AI Penetration TestingHow AI-driven penetration testing continuously covers your attack surface.
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