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.

There are packages installed that are affected by a vulnerability referenced in the following CVE:

  - 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. (CVE-2026-75596)

The remote SUSE Linux SLED15 / SLED_SAP15 / SLES15 / SLES_SAP15 host has packages installed that are affected by multiple vulnerabilities as referenced in the SUSE-SU-2026:4391-1 advisory.

    - CVE-2026-59902: Netty: Memory Exhaustion in SctpMessageCompletionHandler (bsc#1275501).
    - CVE-2026-59903: Netty Vulnerable to Cache Poisoning and Information Disclosure via CORS Vary Header     Overwrite       (bsc#1275500).
    - CVE-2026-62243: TLS hostname verification bypass in Netty OpenSSL client path (bsc#1276455).
    - CVE-2026-62380: null byte and CRLF injection in Socks4ClientEncoder and Socks5ClientEncoder     (bsc#1276456).
    - CVE-2026-75595: fragmented TLS `ClientHello` causes fallback to default `SslContext` and allows for SNI     routing and       mTLS requirement bypass (bsc#1276420).
    - CVE-2026-75596: fragmented `ClientHello`records can trigger quadratic pre-handshake reassembly in     default SNI parsing       (bsc#1276421).
    - CVE-2026-76816: missing input validation in `MqttEncoder` allows for null-byte injection, topic     hijacking, and ACL       bypassing (bsc#1277243).
    - CVE-2026-89044: HTTP request smuggling in Netty via improper validation of final Transfer-Encoding     coding       (bsc#1280048).
    - CVE-2026-93488: Denial of Service via unbounded concurrent SPDY streams (bsc#1282084).
    - CVE-2026-93491: Denial of Service via unbounded HttpServerCodec HTTP/1.1 pipeline queue (bsc#1282085).
    - CVE-2026-93492: HTTP/2 HpackEncoder DoS with large table size (bsc#1282132).
    - CVE-2026-93493: missing `nextUpdate` field in OCSP responses leads to silent validation bypass     (bsc#1281431).
    - CVE-2026-93494: ByteBuf Leak in StompSubframeDecoder When a Frame Body Is Never Terminated     (bsc#1282506).
    - CVE-2026-93558: Unbounded Per-Connection Queue Growth in WebSocketServerExtensionHandler Leads to Denial     of Service       (bsc#1282140).
    - CVE-2026-93560: STOMP codec content-length long-to-int truncation causes infinite decode loop DoS     (bsc#1282141).
    - CVE-2026-93562: Incomplete validation of malformed Transfer-Encoding allows HTTP request smuggling     (bsc#1282362).
    - CVE-2026-93563: unbounded multi-line response accumulation in `SmtpResponseDecoder` leads to memory     exhaustion and a       DoS (bsc#1281432).
    - CVE-2026-93564: HAProxy PROXY-v2 nested-TLV grandchild ByteBuf reference-count leak (bsc#1282363).
    - CVE-2026-93565: RtspDecoder Method-Token Smuggling via Trailing Control Byte (bsc#1282364).
    - CVE-2026-93566: HTTP Request Smuggling due to control characters in the chunk-size line (bsc#1282366).
    - CVE-2026-93567: HTTP/1 authority-form CONNECT is translated to malformed HTTP/2 CONNECT with Host-     controlled       :authority (bsc#1282367).
    - CVE-2026-93568: HTTP/2 and HTTP/3 Extended CONNECT requests are downgraded as regular CONNECT requests     (bsc#1282370).
    - CVE-2026-93569: HTTP/1 absolute-form Host mismatch is translated to HTTP/2 :authority, overriding the     request-target       authority (bsc#1282372).
    - CVE-2026-93572: multiplication of patched preallocation limits in `RedisArrayAggregator` nested RESP     headers can lead       to denial of service (bsc#1281433).
    - CVE-2026-93573: Incomplete validation of malformed Transfer-Encoding allows HTTP request smuggling     (bsc#1282373).
    - CVE-2026-93574: HTTP request smuggling via post-digit whitespace in chunk-size parsing (bsc#1282374).
    - CVE-2026-93575: missing validations in the `MqttDecoder` can lead to excessive resource consumption and     a DoS       (bsc#1281434).
    - CVE-2026-93576: netty-codec-smtp -- SMTP command-name field is not CRLF-validated (bsc#1282507).
    - CVE-2026-93578: missing Extended Key Usage (EKU) check in OCSP client allows certificate revocation     bypass       (bsc#1281435).
    - CVE-2026-93579: HTTP/2 header field values are not validated by default (bsc#1282378).

    Changes for netty:

    - Upgrade to upstream version 4.1.138

    Changes for netty-tcnative:

    - Upgrade to version 2.0.84 Final

Tenable has extracted the preceding description block directly from the SUSE security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

The Linux/Unix host has one or more packages installed that are impacted by a vulnerability without a vendor supplied patch available.

  - 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. (CVE-2026-75596)

Note that Nessus relies on the presence of the package as reported by the vendor.

ID	Name	Product	Family	Type	Severity
455204	Echo: io.netty:netty-handler: security update to 4.1.137.Final	Tenable Cloud Security	Echo Local Security Checks	Local	high
455204	Echo: io.netty:netty-handler: security update to 4.1.137.Final	Tenable Self-Hosted Container Security	Echo Local Security Checks	Local	high
351404	SUSE SLED15 / SLES15 Security Update : netty, netty-tcnative (SUSE-SU-2026:4391-1)	Nessus	SuSE Local Security Checks	Local	critical
338364	Linux Distros Unpatched Vulnerability : CVE-2026-75596	Nessus	Misc.	Local	high

Detections

Analytics

CVE-2026-75596

high

Tenable Plugins

high

high

critical

high