netty — security advisory
Netty is an asynchronous, event-driven network application framework. Prior to 4.1.137.Final and 4.2.17.Final, the default io.netty.handler.ssl.SniHandler constructors use the pre-handshake ClientHello aggregation path in handler/src/main/java/io/netty/handler/ssl/SslClientHelloHandler.java at io.netty.handler.ssl.SslClientHelloHandler#decode, where handshakeBuffer.clear() and writeBytes() recopy all previously received body bytes for every additional TLS record. An unauthenticated remote peer can advertise a large ClientHello and deliver its body in thousands of tiny records, causing quadratic CPU work on the event loop before the TLS handshake completes and degrading TLS handling for other clients. This issue is fixed in versions 4.1.137.Final and 4.2.17.Final.
- Products
- netty
- Affected versions
- 1:4.1.48-10, 1:4.1.48-10+deb13u1, 1:4.1.48-11, 1:4.1.48-12, 1:4.1.48-13, 1:4.1.48-14, 1:4.1.48-15, 1:4.1.48-16, 1:4.1.48-7, 1:4.1.48-7+deb12u1, 1:4.1.48-7+deb12u2, 1:4.1.48-8, 1:4.1.48-9
- Fixed versions
- Not specified
- CVEs
- CVE-2026-75596
- Confirmed fixed CVEs
- Not specified
- Updated in this feed
- 1 Nov 2026, 17:49 UTC · Revision 1
Source evidence
Netty is an asynchronous, event-driven network application framework. Prior to 4.1.137.Final and 4.2.17.Final, the default io.netty.handler.ssl.SniHandler constructors use the pre-handshake ClientHello aggregation path in handler/src/main/java/io/netty/handler/ssl/SslClientHelloHandler.java at io.netty.handler.ssl.SslClientHelloHandler#decode, where handshakeBuffer.clear() and writeBytes() recopy all previously received body bytes for every additional TLS record. An unauthenticated remote peer can advertise a large ClientHello and deliver its body in thousands of tiny records, causing quadratic CPU work on the event loop before the TLS handshake completes and degrading TLS handling for other clients. This issue is fixed in versions 4.1.137.Final and 4.2.17.Final.
osv:DEBIAN-CVE-2026-75596
netty
Fixed versions: Not specified
netty
Fixed versions: Not specified
netty
Fixed versions: Not specified
Complete source record
{
"id": "588ababf083414f7b60a1c6b8e1af2d64dadbe67f66ca71d0f516c5a1e17afd9",
"url": "https://osv.dev/vulnerability/DEBIAN-CVE-2026-75596",
"method": "structured",
"payload": {
"kind": "advisory",
"title": "DEBIAN-CVE-2026-75596",
"summary": "Netty is an asynchronous, event-driven network application framework. Prior to 4.1.137.Final and 4.2.17.Final, the default io.netty.handler.ssl.SniHandler constructors use the pre-handshake ClientHello aggregation path in handler/src/main/java/io/netty/handler/ssl/SslClientHelloHandler.java at io.netty.handler.ssl.SslClientHelloHandler#decode, where handshakeBuffer.clear() and writeBytes() recopy all previously received body bytes for every additional TLS record. An unauthenticated remote peer can advertise a large ClientHello and deliver its body in thousands of tiny records, causing quadratic CPU work on the event loop before the TLS handshake completes and degrading TLS handling for other clients. This issue is fixed in versions 4.1.137.Final and 4.2.17.Final.",
"evidence": "osv:DEBIAN-CVE-2026-75596",
"products": [
{
"name": {
"value": "netty",
"evidence": "/affected/0/package/name"
},
"prerequisites": [],
"fixed_versions": [],
"affected_versions": [
{
"value": "1:4.1.48-10",
"evidence": "/affected/0/versions"
},
{
"value": "1:4.1.48-11",
"evidence": "/affected/0/versions"
},
{
"value": "1:4.1.48-12",
"evidence": "/affected/0/versions"
},
{
"value": "1:4.1.48-13",
"evidence": "/affected/0/versions"
},
{
"value": "1:4.1.48-14",
"evidence": "/affected/0/versions"
},
{
"value": "1:4.1.48-15",
"evidence": "/affected/0/versions"
},
{
"value": "1:4.1.48-16",
"evidence": "/affected/0/versions"
},
{
"value": "1:4.1.48-7",
"evidence": "/affected/0/versions"
},
{
"value": "1:4.1.48-7+deb12u1",
"evidence": "/affected/0/versions"
},
{
"value": "1:4.1.48-7+deb12u2",
"evidence": "/affected/0/versions"
},
{
"value": "1:4.1.48-8",
"evidence": "/affected/0/versions"
},
{
"value": "1:4.1.48-9",
"evidence": "/affected/0/versions"
}
]
},
{
"name": {
"value": "netty",
"evidence": "/affected/1/package/name"
},
"prerequisites": [],
"fixed_versions": [],
"affected_versions": [
{
"value": "1:4.1.48-10",
"evidence": "/affected/1/versions"
},
{
"value": "1:4.1.48-10+deb13u1",
"evidence": "/affected/1/versions"
},
{
"value": "1:4.1.48-11",
"evidence": "/affected/1/versions"
},
{
"value": "1:4.1.48-12",
"evidence": "/affected/1/versions"
},
{
"value": "1:4.1.48-13",
"evidence": "/affected/1/versions"
},
{
"value": "1:4.1.48-14",
"evidence": "/affected/1/versions"
},
{
"value": "1:4.1.48-15",
"evidence": "/affected/1/versions"
},
{
"value": "1:4.1.48-16",
"evidence": "/affected/1/versions"
}
]
},
{
"name": {
"value": "netty",
"evidence": "/affected/2/package/name"
},
"prerequisites": [],
"fixed_versions": [],
"affected_versions": [
{
"value": "1:4.1.48-10",
"evidence": "/affected/2/versions"
},
{
"value": "1:4.1.48-11",
"evidence": "/affected/2/versions"
},
{
"value": "1:4.1.48-12",
"evidence": "/affected/2/versions"
},
{
"value": "1:4.1.48-13",
"evidence": "/affected/2/versions"
},
{
"value": "1:4.1.48-14",
"evidence": "/affected/2/versions"
},
{
"value": "1:4.1.48-15",
"evidence": "/affected/2/versions"
},
{
"value": "1:4.1.48-16",
"evidence": "/affected/2/versions"
}
]
}
],
"severity": "high",
"structured": {
"id": "DEBIAN-CVE-2026-75596",
"aliases": [
"DEBIAN-CVE-2026-75596"
],
"metrics": [
{
"type": "CVSS_V3",
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"
}
],
"affected": [
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "0"
}
]
}
],
"package": {
"name": "netty",
"purl": "pkg:deb/debian/netty?arch=source&distro=bookworm",
"ecosystem": "Debian:12"
},
"versions": [
"1:4.1.48-10",
"1:4.1.48-11",
"1:4.1.48-12",
"1:4.1.48-13",
"1:4.1.48-14",
"1:4.1.48-15",
"1:4.1.48-16",
"1:4.1.48-7",
"1:4.1.48-7+deb12u1",
"1:4.1.48-7+deb12u2",
"1:4.1.48-8",
"1:4.1.48-9"
],
"database_specific": {
"source": "https://storage.googleapis.com/debian-osv/debian-cve-osv/DEBIAN-CVE-2026-75596.json"
},
"ecosystem_specific": {
"urgency": "not yet assigned"
}
},
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "0"
}
]
}
],
"package": {
"name": "netty",
"purl": "pkg:deb/debian/netty?arch=source&distro=trixie",
"ecosystem": "Debian:13"
},
"versions": [
"1:4.1.48-10",
"1:4.1.48-10+deb13u1",
"1:4.1.48-11",
"1:4.1.48-12",
"1:4.1.48-13",
"1:4.1.48-14",
"1:4.1.48-15",
"1:4.1.48-16"
],
"database_specific": {
"source": "https://storage.googleapis.com/debian-osv/debian-cve-osv/DEBIAN-CVE-2026-75596.json"
},
"ecosystem_specific": {
"urgency": "not yet assigned"
}
},
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "0"
}
]
}
],
"package": {
"name": "netty",
"purl": "pkg:deb/debian/netty?arch=source&distro=forky",
"ecosystem": "Debian:14"
},
"versions": [
"1:4.1.48-10",
"1:4.1.48-11",
"1:4.1.48-12",
"1:4.1.48-13",
"1:4.1.48-14",
"1:4.1.48-15",
"1:4.1.48-16"
],
"database_specific": {
"source": "https://storage.googleapis.com/debian-osv/debian-cve-osv/DEBIAN-CVE-2026-75596.json"
},
"ecosystem_specific": {
"urgency": "not yet assigned"
}
}
],
"modified": "2026-10-27T09:47:37.977312228Z",
"provider": "osv",
"upstream": [
"CVE-2026-75596"
],
"references": [
"https://security-tracker.debian.org/tracker/CVE-2026-75596"
]
},
"related_cves": [
{
"value": "CVE-2026-75596",
"evidence": "/upstream"
}
],
"security_relevant": true,
"severity_evidence": "/severity/0/score"
},
"source_id": "core-osv",
"document_id": 461301,
"published_at": "2026-08-19T21:17:37.74+00:00"
}