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CVE-2021-3618

HIGHCVSS 7.4/10EPSS 2.04%

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
7.4/10

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

EPSS Probability
2.04%

78.6th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

Affected Software

VendorProductVersions
F5Nginx< 1.21.0
SendmailSendmail< 8.17
Vsftpd ProjectVsftpd< 3.0.4
FedoraprojectFedora33
FedoraprojectFedora34
FedoraprojectFedora35
DebianDebian Linux10.0

References

Timeline

Published
Last Modified
Status
Modified

Frequently Asked Questions

What is 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.
How severe is CVE-2021-3618?
CVE-2021-3618 has a CVSS score of 7.4/10 (HIGH severity). The EPSS model estimates a 2.04% probability of exploitation in the next 30 days.
How do I fix CVE-2021-3618?
Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2021-3618?

Run a free Strix scan to check your systems for this vulnerability.

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Source: NVD / NIST