High
Security advisory
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.
- Products
- Not specified
- Affected versions
- Not specified
- Fixed versions
- Not specified
- CVEs
- CVE-2021-3618
- Confirmed fixed CVEs
- Not specified
- Updated in this feed
- 1 Nov 2026, 06:34 UTC · Revision 1
Source evidence
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.
osv:CVE-2021-3618
Complete source record
{
"id": "d36e4de214c13b324d7cad0f31ff075685fa4ca6761351bce18bc401428e0848",
"url": "https://osv.dev/vulnerability/CVE-2021-3618",
"method": "structured",
"payload": {
"kind": "advisory",
"title": "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.",
"evidence": "osv:CVE-2021-3618",
"products": [],
"severity": "high",
"structured": {
"id": "CVE-2021-3618",
"aliases": [
"BIT-nginx-2021-3618",
"BIT-nginx-gateway-2021-3618",
"CVE-2021-3618"
],
"metrics": [
{
"type": "CVSS_V3",
"score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N"
}
],
"affected": [
{
"ranges": [
{
"repo": "https://github.com/nginx/nginx",
"type": "GIT",
"events": [
{
"introduced": "0"
},
{
"fixed": "ffcf93a6bf0c203c136e9ee9d65b81659ca9f7b6"
}
],
"database_specific": {
"extracted_events": [
{
"cpe": "cpe:2.3:a:f5:nginx:*:*:*:*:*:*:*:*",
"range": [
{
"introduced": "0"
},
{
"fixed": "1.21.0"
}
],
"source": "CPE_RANGE"
}
]
}
}
],
"versions": [
"release-1.19.10",
"release-1.19.9",
"release-1.19.8",
"release-1.19.7",
"release-1.19.6",
"release-1.19.5",
"release-1.19.4",
"release-1.19.3",
"release-1.19.2",
"release-1.19.1",
"release-1.19.0",
"release-1.17.10",
"release-1.17.9",
"release-1.17.8",
"release-1.17.7",
"release-1.17.6",
"release-1.17.5",
"release-1.17.4",
"release-1.17.3",
"release-1.17.2",
"release-1.17.1",
"release-1.17.0",
"release-1.15.12",
"release-1.15.11",
"release-1.15.10",
"release-1.15.9",
"release-1.15.8",
"release-1.15.7",
"release-1.15.6",
"release-1.15.5",
"release-1.15.4",
"release-1.15.3",
"release-1.15.2",
"release-1.15.1",
"release-1.15.0",
"release-1.13.12",
"release-1.13.11",
"release-1.13.10",
"release-1.13.9",
"release-1.13.8",
"release-1.13.7",
"release-1.13.6",
"release-1.13.5",
"release-1.13.4",
"release-1.13.3",
"release-1.13.2",
"release-1.13.1",
"release-1.13.0",
"release-1.11.13",
"release-1.11.12",
"release-1.11.11",
"release-1.11.10",
"release-1.11.9",
"release-1.11.8",
"release-1.11.7",
"release-1.11.6",
"release-1.11.5",
"release-1.11.4",
"release-1.11.3",
"release-1.11.2",
"release-1.11.1",
"release-1.11.0",
"release-1.9.15",
"release-1.9.14",
"release-1.9.13",
"release-1.9.12",
"release-1.9.11",
"release-1.9.10",
"release-1.9.9",
"release-1.9.8",
"release-1.9.7",
"release-1.9.6",
"release-1.9.5",
"release-1.9.4",
"release-1.9.3",
"release-1.9.2",
"release-1.9.1",
"release-1.9.0",
"release-1.7.12",
"release-1.7.11",
"release-1.7.10",
"release-1.7.9",
"release-1.7.8",
"release-1.7.7",
"release-1.7.6",
"release-1.7.5",
"release-1.7.4",
"release-1.7.3",
"release-1.7.2",
"release-1.7.1",
"release-1.7.0",
"release-1.5.13",
"release-1.5.12",
"release-1.5.11",
"release-1.5.10",
"release-1.5.9",
"release-1.5.8",
"release-1.5.7",
"release-1.5.6",
"release-1.5.5",
"release-1.5.4",
"release-1.5.3",
"release-1.5.2",
"release-1.5.1",
"release-1.5.0",
"release-1.4.0",
"release-1.3.16",
"release-1.3.15",
"release-1.3.14",
"release-1.3.13",
"release-1.3.12",
"release-1.3.11",
"release-1.3.10",
"release-1.3.9",
"release-1.3.8",
"release-1.3.7",
"release-1.3.6",
"release-1.3.5",
"release-1.3.4",
"release-1.3.3",
"release-1.3.2",
"release-1.3.1",
"release-1.3.0",
"release-1.2.0",
"release-1.1.19",
"release-1.1.18",
"release-1.1.17",
"release-1.1.16",
"release-1.1.15",
"release-1.1.14",
"release-1.1.13",
"release-1.1.12",
"release-1.1.11",
"release-1.1.10",
"release-1.1.9",
"release-1.1.8",
"release-1.1.7",
"release-1.1.6",
"release-1.1.5",
"release-1.1.4",
"release-1.1.3",
"release-1.1.2",
"release-1.1.1",
"release-1.1.0",
"release-1.0.5",
"release-1.0.4",
"release-1.0.3",
"release-1.0.2",
"release-1.0.1",
"release-1.0.0",
"release-0.9.7",
"release-0.9.6",
"release-0.9.5",
"release-0.9.4",
"release-0.9.3",
"release-0.9.2",
"release-0.9.1",
"release-0.9.0",
"release-0.8.53",
"release-0.8.52",
"release-0.8.51",
"release-0.8.50",
"release-0.8.49",
"release-0.8.48",
"release-0.8.47",
"release-0.8.46",
"release-0.8.45",
"release-0.8.44",
"release-0.8.43",
"release-0.8.42",
"release-0.8.41",
"release-0.8.40",
"release-0.8.39",
"release-0.8.38",
"release-0.8.37",
"release-0.8.36",
"release-0.8.35",
"release-0.8.34",
"release-0.8.33",
"release-0.8.32",
"release-0.8.31",
"release-0.8.30",
"release-0.8.29",
"release-0.8.28",
"release-0.8.27",
"release-0.8.26",
"release-0.8.25",
"release-0.8.24",
"release-0.8.23",
"release-0.8.22",
"release-0.8.21",
"release-0.8.20",
"release-0.8.19",
"release-0.8.18",
"release-0.8.17",
"release-0.8.16",
"release-0.8.15",
"release-0.8.14",
"release-0.8.13",
"release-0.8.12",
"release-0.8.11",
"release-0.8.10",
"release-0.8.9",
"release-0.8.8",
"release-0.8.7",
"release-0.8.6",
"release-0.8.5",
"release-0.8.4",
"release-0.8.3",
"release-0.8.2",
"release-0.8.1",
"release-0.8.0",
"release-0.7.59",
"release-0.7.58",
"release-0.7.57",
"release-0.7.56",
"release-0.7.55",
"release-0.7.54",
"release-0.7.53",
"release-0.7.52",
"release-0.7.51",
"release-0.7.50",
"release-0.7.49",
"release-0.7.48",
"release-0.7.47",
"release-0.7.46",
"release-0.7.45",
"release-0.7.44",
"release-0.7.43",
"release-0.7.42",
"release-0.7.41",
"release-0.7.40",
"release-0.7.39",
"release-0.7.38",
"release-0.7.37",
"release-0.7.36",
"release-0.7.35",
"release-0.7.34",
"release-0.7.33",
"release-0.7.32",
"release-0.7.31",
"release-0.7.30",
"release-0.7.29",
"release-0.7.28",
"release-0.7.27",
"release-0.7.26",
"release-0.7.25",
"release-0.7.24",
"release-0.7.23",
"release-0.7.22",
"release-0.7.21",
"release-0.7.20",
"release-0.7.19",
"release-0.7.18",
"release-0.7.17",
"release-0.7.16",
"release-0.7.15",
"release-0.7.14",
"release-0.7.13",
"release-0.7.12",
"release-0.7.11",
"release-0.7.10",
"release-0.7.9",
"release-0.7.8",
"release-0.7.7",
"release-0.7.6",
"release-0.7.5",
"release-0.7.4",
"release-0.7.3",
"release-0.7.2",
"release-0.7.1",
"release-0.7.0",
"release-0.6.31",
"release-0.6.30",
"release-0.6.29",
"release-0.6.28",
"release-0.6.27",
"release-0.6.26",
"release-0.6.25",
"release-0.6.24",
"release-0.6.23",
"release-0.6.22",
"release-0.6.21",
"release-0.6.20",
"release-0.6.19",
"release-0.6.18",
"release-0.6.17",
"release-0.6.16",
"release-0.6.15",
"release-0.6.14",
"release-0.6.13",
"release-0.6.12",
"release-0.6.11",
"release-0.6.10",
"release-0.6.9",
"release-0.6.8",
"release-0.6.7",
"release-0.6.6",
"release-0.6.5",
"release-0.6.4",
"release-0.6.3",
"release-0.6.2",
"release-0.6.1",
"release-0.6.0",
"release-0.5.25",
"release-0.5.24",
"release-0.5.23",
"release-0.5.22",
"release-0.5.21",
"release-0.5.20",
"release-0.5.19",
"release-0.5.18",
"release-0.5.17",
"release-0.5.16",
"release-0.5.15",
"release-0.5.14",
"release-0.5.13",
"release-0.5.12",
"release-0.5.11",
"release-0.5.10",
"release-0.5.9",
"release-0.5.8",
"release-0.5.7",
"release-0.5.6",
"release-0.5.5",
"release-0.5.4",
"release-0.5.3",
"release-0.5.2",
"release-0.5.1",
"release-0.5.0",
"release-0.4.14",
"release-0.4.13",
"release-0.4.12",
"release-0.4.11",
"release-0.4.10",
"release-0.4.9",
"release-0.4.8",
"release-0.4.7",
"release-0.4.6",
"release-0.4.5",
"release-0.4.4",
"release-0.4.3",
"release-0.4.2",
"release-0.4.1",
"release-0.4.0",
"release-0.3.61",
"release-0.3.60",
"release-0.3.59",
"release-0.3.58",
"release-0.3.57",
"release-0.3.56",
"release-0.3.55",
"release-0.3.54",
"release-0.3.53",
"release-0.3.52",
"release-0.3.51",
"release-0.3.50",
"release-0.3.49",
"release-0.3.48",
"release-0.3.47",
"release-0.3.46",
"release-0.3.45",
"release-0.3.44",
"release-0.3.43",
"release-0.3.42",
"release-0.3.41",
"release-0.3.40",
"release-0.3.39",
"release-0.3.38",
"release-0.3.37",
"release-0.3.36",
"release-0.3.35",
"release-0.3.34",
"release-0.3.33",
"release-0.3.32",
"release-0.3.31",
"release-0.3.30",
"release-0.3.29",
"release-0.3.28",
"release-0.3.27",
"release-0.3.26",
"release-0.3.25",
"release-0.3.24",
"release-0.3.23",
"release-0.3.22",
"release-0.3.21",
"release-0.3.20",
"release-0.3.19",
"release-0.3.18",
"release-0.3.17",
"release-0.3.16",
"release-0.3.15",
"release-0.3.14",
"release-0.3.13",
"release-0.3.12",
"release-0.3.11",
"release-0.3.10",
"release-0.3.9",
"release-0.3.8",
"release-0.3.7",
"release-0.3.6",
"release-0.3.5",
"release-0.3.4",
"release-0.3.3",
"release-0.3.2",
"release-0.3.1",
"release-0.3.0",
"release-0.2.6",
"release-0.2.5",
"release-0.2.4",
"release-0.2.3",
"release-0.2.2",
"release-0.2.1",
"release-0.2.0",
"release-0.1.45",
"release-0.1.44",
"release-0.1.43",
"release-0.1.42",
"release-0.1.41",
"release-0.1.40",
"release-0.1.39",
"release-0.1.38",
"release-0.1.37",
"release-0.1.36",
"release-0.1.35",
"release-0.1.34",
"release-0.1.33",
"release-0.1.32",
"release-0.1.31",
"release-0.1.30",
"release-0.1.29",
"release-0.1.28",
"release-0.1.27",
"release-0.1.26",
"release-0.1.25",
"release-0.1.24",
"release-0.1.23",
"release-0.1.22",
"release-0.1.21",
"release-0.1.20",
"release-0.1.19",
"release-0.1.18",
"release-0.1.17",
"release-0.1.16",
"release-0.1.15",
"release-0.1.14",
"release-0.1.13",
"release-0.1.12",
"release-0.1.11",
"release-0.1.10",
"release-0.1.9",
"release-0.1.8",
"release-0.1.7",
"release-0.1.6",
"release-0.1.5",
"release-0.1.4",
"release-0.1.3",
"release-0.1.2",
"release-0.1.1",
"release-0.1.0"
],
"database_specific": {
"source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2021-3618.json"
}
}
],
"modified": "2026-10-24T10:30:41.363399125Z",
"provider": "osv",
"references": [
"https://alpaca-attack.com/",
"https://lists.debian.org/debian-lts-announce/2022/11/msg00031.html",
"https://bugzilla.redhat.com/show_bug.cgi?id=1975623"
],
"provider_metadata": {
"unresolved_ranges": [
{
"cpes": [
"cpe:2.3:a:sendmail:sendmail:*:*:*:*:*:*:*:*"
],
"vendor_product": "sendmail:sendmail",
"extracted_events": [
{
"range": [
{
"fixed": "8.17"
}
],
"source": "CPE_RANGE"
}
]
},
{
"cpes": [
"cpe:2.3:a:vsftpd_project:vsftpd:*:*:*:*:*:*:*:*"
],
"vendor_product": "vsftpd_project:vsftpd",
"extracted_events": [
{
"range": [
{
"fixed": "3.0.4"
}
],
"source": "CPE_RANGE"
}
]
},
{
"cpes": [
"cpe:2.3:o:debian:debian_linux:10.0:*:*:*:*:*:*:*"
],
"vendor_product": "debian:debian_linux",
"extracted_events": [
{
"range": [
{
"introduced": "10.0"
},
{
"last_affected": "10.0"
}
],
"source": "CPE_STRING"
}
]
},
{
"cpes": [
"cpe:2.3:o:fedoraproject:fedora:33:*:*:*:*:*:*:*",
"cpe:2.3:o:fedoraproject:fedora:34:*:*:*:*:*:*:*",
"cpe:2.3:o:fedoraproject:fedora:35:*:*:*:*:*:*:*"
],
"vendor_product": "fedoraproject:fedora",
"extracted_events": [
{
"range": [
{
"introduced": "33"
},
{
"last_affected": "33"
},
{
"introduced": "34"
},
{
"last_affected": "34"
},
{
"introduced": "35"
},
{
"last_affected": "35"
}
],
"source": "CPE_STRING"
}
]
}
]
}
},
"related_cves": [
{
"value": "CVE-2021-3618",
"evidence": "/id"
}
],
"security_relevant": true,
"severity_evidence": "/severity/0/score"
},
"source_id": "core-osv",
"document_id": 435138,
"published_at": "2022-03-23T20:15:09.833+00:00"
}