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Vulnerability details: VCID-3d3j-83ap-jua7
Vulnerability ID VCID-3d3j-83ap-jua7
Aliases CVE-2021-3618
Summary 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.
Status Published
Exploitability 0.5
Weighted Severity 6.7
Risk 3.4
Affected and Fixed Packages Package Details
Weaknesses (1)
CWE-295 Improper Certificate Validation
System Score Found at
cvssv3 7.4 https://access.redhat.com/hydra/rest/securitydata/cve/CVE-2021-3618.json
epss 0.00197 https://api.first.org/data/v1/epss?cve=CVE-2021-3618
epss 0.00197 https://api.first.org/data/v1/epss?cve=CVE-2021-3618
epss 0.00197 https://api.first.org/data/v1/epss?cve=CVE-2021-3618
epss 0.00375 https://api.first.org/data/v1/epss?cve=CVE-2021-3618
epss 0.00375 https://api.first.org/data/v1/epss?cve=CVE-2021-3618
epss 0.00375 https://api.first.org/data/v1/epss?cve=CVE-2021-3618
epss 0.00375 https://api.first.org/data/v1/epss?cve=CVE-2021-3618
epss 0.00375 https://api.first.org/data/v1/epss?cve=CVE-2021-3618
epss 0.00375 https://api.first.org/data/v1/epss?cve=CVE-2021-3618
epss 0.00375 https://api.first.org/data/v1/epss?cve=CVE-2021-3618
epss 0.00375 https://api.first.org/data/v1/epss?cve=CVE-2021-3618
epss 0.00375 https://api.first.org/data/v1/epss?cve=CVE-2021-3618
epss 0.00384 https://api.first.org/data/v1/epss?cve=CVE-2021-3618
epss 0.00384 https://api.first.org/data/v1/epss?cve=CVE-2021-3618
epss 0.00384 https://api.first.org/data/v1/epss?cve=CVE-2021-3618
epss 0.00384 https://api.first.org/data/v1/epss?cve=CVE-2021-3618
epss 0.00384 https://api.first.org/data/v1/epss?cve=CVE-2021-3618
epss 0.00384 https://api.first.org/data/v1/epss?cve=CVE-2021-3618
cvssv3.1 7.4 https://ftp.suse.com/pub/projects/security/yaml/suse-cvss-scores.yaml
cvssv2 5.8 https://nvd.nist.gov/vuln/detail/CVE-2021-3618
cvssv3.1 7.4 https://nvd.nist.gov/vuln/detail/CVE-2021-3618
archlinux Medium https://security.archlinux.org/AVG-2101
archlinux Medium https://security.archlinux.org/AVG-2102
archlinux Medium https://security.archlinux.org/AVG-2103
Reference id Reference type URL
https://access.redhat.com/hydra/rest/securitydata/cve/CVE-2021-3618.json
https://alpaca-attack.com/
https://api.first.org/data/v1/epss?cve=CVE-2021-3618
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-3618
https://ftp.suse.com/pub/projects/security/yaml/suse-cvss-scores.yaml
1975623 https://bugzilla.redhat.com/show_bug.cgi?id=1975623
991328 https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=991328
AVG-2101 https://security.archlinux.org/AVG-2101
AVG-2102 https://security.archlinux.org/AVG-2102
AVG-2103 https://security.archlinux.org/AVG-2103
cpe:2.3:a:f5:nginx:*:*:*:*:*:*:*:* https://nvd.nist.gov/vuln/search/results?adv_search=true&isCpeNameSearch=true&query=cpe:2.3:a:f5:nginx:*:*:*:*:*:*:*:*
cpe:2.3:a:sendmail:sendmail:*:*:*:*:*:*:*:* https://nvd.nist.gov/vuln/search/results?adv_search=true&isCpeNameSearch=true&query=cpe:2.3:a:sendmail:sendmail:*:*:*:*:*:*:*:*
cpe:2.3:a:vsftpd_project:vsftpd:*:*:*:*:*:*:*:* https://nvd.nist.gov/vuln/search/results?adv_search=true&isCpeNameSearch=true&query=cpe:2.3:a:vsftpd_project:vsftpd:*:*:*:*:*:*:*:*
cpe:2.3:o:debian:debian_linux:10.0:*:*:*:*:*:*:* https://nvd.nist.gov/vuln/search/results?adv_search=true&isCpeNameSearch=true&query=cpe:2.3:o:debian:debian_linux:10.0:*:*:*:*:*:*:*
cpe:2.3:o:fedoraproject:fedora:33:*:*:*:*:*:*:* https://nvd.nist.gov/vuln/search/results?adv_search=true&isCpeNameSearch=true&query=cpe:2.3:o:fedoraproject:fedora:33:*:*:*:*:*:*:*
cpe:2.3:o:fedoraproject:fedora:34:*:*:*:*:*:*:* https://nvd.nist.gov/vuln/search/results?adv_search=true&isCpeNameSearch=true&query=cpe:2.3:o:fedoraproject:fedora:34:*:*:*:*:*:*:*
cpe:2.3:o:fedoraproject:fedora:35:*:*:*:*:*:*:* https://nvd.nist.gov/vuln/search/results?adv_search=true&isCpeNameSearch=true&query=cpe:2.3:o:fedoraproject:fedora:35:*:*:*:*:*:*:*
CVE-2021-3618 https://nvd.nist.gov/vuln/detail/CVE-2021-3618
USN-5371-1 https://usn.ubuntu.com/5371-1/
USN-5371-2 https://usn.ubuntu.com/5371-2/
USN-6379-1 https://usn.ubuntu.com/6379-1/
No exploits are available.
Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N Found at https://access.redhat.com/hydra/rest/securitydata/cve/CVE-2021-3618.json
Attack Vector (AV) Attack Complexity (AC) Privileges Required (PR) User Interaction (UI) Scope (S) Confidentiality Impact (C) Integrity Impact (I) Availability Impact (A)

network

adjacent_network

local

physical

low

high

none

low

high

none

required

unchanged

changed

high

low

none

high

low

none

high

low

none
Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N Found at https://ftp.suse.com/pub/projects/security/yaml/suse-cvss-scores.yaml
Attack Vector (AV) Attack Complexity (AC) Privileges Required (PR) User Interaction (UI) Scope (S) Confidentiality Impact (C) Integrity Impact (I) Availability Impact (A)

network

adjacent_network

local

physical

low

high

none

low

high

none

required

unchanged

changed

high

low

none

high

low

none

high

low

none
Vector: AV:N/AC:M/Au:N/C:P/I:P/A:N Found at https://nvd.nist.gov/vuln/detail/CVE-2021-3618
Exploitability (E) Access Vector (AV) Access Complexity (AC) Authentication (Au) Confidentiality Impact (C) Integrity Impact (I) Availability Impact (A)

high

functional

unproven

proof_of_concept

not_defined

local

adjacent_network

network

high

medium

low

multiple

single

none

none

partial

complete

none

partial

complete

none

partial

complete
Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N Found at https://nvd.nist.gov/vuln/detail/CVE-2021-3618
Attack Vector (AV) Attack Complexity (AC) Privileges Required (PR) User Interaction (UI) Scope (S) Confidentiality Impact (C) Integrity Impact (I) Availability Impact (A)

network

adjacent_network

local

physical

low

high

none

low

high

none

required

unchanged

changed

high

low

none

high

low

none

high

low

none
Exploit Prediction Scoring System (EPSS)
Percentile 0.42322
EPSS Score 0.00197
Published At Aug. 1, 2025, 12:55 p.m.
Date Actor Action Source VulnerableCode Version
2025-07-31T08:35:17.452503+00:00 Alpine Linux Importer Import https://secdb.alpinelinux.org/edge/main.json 37.0.0