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CVE-2026-76816

Netty: MQTT Topic Name and Client ID Validation Bypass

3.5 LowFix available

Netty is an asynchronous, event-driven network application framework. Prior to versions 4.1.137.Final and 4.2.17.Final, MqttEncoder does not validate client identifiers, will topics, usernames, and PUBLISH topic names before encoding, allowing prohibited null bytes in MQTT UTF-8 string fields and potentially causing routing, access-control, or identity mismatches in downstream brokers. The vulnerability is exploitable when an application uses Netty's MQTT encoder to construct messages from user-controlled input. This issue is fixed in versions 4.1.137.Final and 4.2.17.Final.

Attack profile

How easy it is to exploit

Attack vector
Adjacent network
Complexity
Low
Privileges needed
Low
User interaction
None

What an attacker can affect

Confidentiality
None
Integrity
Low
Availability
None

Exploit likelihood

0.17%Unchanged since Aug 25, 2026
90%50%10%1%

What each source reports

CVE List Score used 3.5

Netty: MQTT Topic Name and Client ID Validation Bypass

Netty is an asynchronous, event-driven network application framework. Prior to versions 4.1.137.Final and 4.2.17.Final, MqttEncoder does not validate client identifiers, will topics, usernames, and PUBLISH topic names before encoding, allowing prohibited null bytes in MQTT UTF-8 string fields and potentially causing routing, access-control, or identity mismatches in downstream brokers. The vulnerability is exploitable when an application uses Netty's MQTT encoder to construct messages from user-controlled input. This issue is fixed in versions 4.1.137.Final and 4.2.17.Final.

Record
CVE-2026-76816
CVSS 3.1
3.5 LowCVSS:3.1/AV:A/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N
Weakness
CWE-20, CWE-626
Updated
2026-11-02
EUVDEUVD-2026-65093 3.5

Netty is an asynchronous, event-driven network application framework. Prior to versions 4.1.137.Final and 4.2.17.Final, MqttEncoder does not validate client identifiers, will topics, usernames, and PUBLISH topic names before encoding, allowing prohibited null bytes in MQTT UTF-8 string fields and potentially causing routing, access-control, or identity mismatches in downstream brokers. The vulnerability is exploitable when an application uses Netty's MQTT encoder to construct messages from user-controlled input. This issue is fixed in versions 4.1.137.Final and 4.2.17.Final.

Record
EUVD-2026-65093
CVSS 3.1
3.5 LowCVSS:3.1/AV:A/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N
Updated
2026-11-02
NVD 3.5

Netty is an asynchronous, event-driven network application framework. Prior to versions 4.1.137.Final and 4.2.17.Final, MqttEncoder does not validate client identifiers, will topics, usernames, and PUBLISH topic names before encoding, allowing prohibited null bytes in MQTT UTF-8 string fields and potentially causing routing, access-control, or identity mismatches in downstream brokers. The vulnerability is exploitable when an application uses Netty's MQTT encoder to construct messages from user-controlled input. This issue is fixed in versions 4.1.137.Final and 4.2.17.Final.

Record
CVE-2026-76816
CVSS 3.1
3.5 LowCVSS:3.1/AV:A/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N
Weakness
CWE-20, CWE-626
Updated
2026-11-02
OSV 3.5

Netty: MQTT Topic Name and Client ID Validation Bypass

Netty is an asynchronous, event-driven network application framework. Prior to versions 4.1.137.Final and 4.2.17.Final, MqttEncoder does not validate client identifiers, will topics, usernames, and PUBLISH topic names before encoding, allowing prohibited null bytes in MQTT UTF-8 string fields and potentially causing routing, access-control, or identity mismatches in downstream brokers. The vulnerability is exploitable when an application uses Netty's MQTT encoder to construct messages from user-controlled input. This issue is fixed in versions 4.1.137.Final and 4.2.17.Final.

Record
CVE-2026-76816
CVSS 3.1
3.5 LowCVSS:3.1/AV:A/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N
Weakness
CWE-20, CWE-626
Updated
2026-11-02
OSVDEBIAN-CVE-2026-76816 3.5

Netty is an asynchronous, event-driven network application framework. Prior to versions 4.1.137.Final and 4.2.17.Final, MqttEncoder does not validate client identifiers, will topics, usernames, and PUBLISH topic names before encoding, allowing prohibited null bytes in MQTT UTF-8 string fields and potentially causing routing, access-control, or identity mismatches in downstream brokers. The vulnerability is exploitable when an application uses Netty's MQTT encoder to construct messages from user-controlled input. This issue is fixed in versions 4.1.137.Final and 4.2.17.Final.

Record
DEBIAN-CVE-2026-76816
CVSS 3.1
3.5 LowCVSS:3.1/AV:A/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N
Updated
2026-11-02
OSVUBUNTU-CVE-2026-76816 3.5

Netty is an asynchronous, event-driven network application framework. Prior to versions 4.1.137.Final and 4.2.17.Final, MqttEncoder does not validate client identifiers, will topics, usernames, and PUBLISH topic names before encoding, allowing prohibited null bytes in MQTT UTF-8 string fields and potentially causing routing, access-control, or identity mismatches in downstream brokers. The vulnerability is exploitable when an application uses Netty's MQTT encoder to construct messages from user-controlled input. This issue is fixed in versions 4.1.137.Final and 4.2.17.Final.

Record
UBUNTU-CVE-2026-76816
CVSS 3.1
3.5 LowCVSS:3.1/AV:A/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N
Updated
2026-11-02
OSVopenSUSE-SU-2026:11882-1 No score

netty-4.1.138-1.1 on GA media

These are all security issues fixed in the netty-4.1.138-1.1 package on the GA media of openSUSE Tumbleweed.

Record
openSUSE-SU-2026:11882-1
Updated
2026-11-02
OSVSUSE-SU-2026:4391-1 No score

Security update for netty, netty-tcnative

This update for netty, netty-tcnative fixes the following issues:

  • 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 ClientHellorecords 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
Record
SUSE-SU-2026:4391-1
Updated
2026-11-02

Affected products

Affected packages

Affected packages
PackageAffectedFixed
netty
Debian:12
All versions, plus listed versions
1:4.1.48-101:4.1.48-111:4.1.48-121:4.1.48-131:4.1.48-14
Show 7 moreShow less
1:4.1.48-151:4.1.48-161:4.1.48-71:4.1.48-7+deb12u11:4.1.48-7+deb12u21:4.1.48-81:4.1.48-9
None known
netty
Debian:13
All versions, plus listed versions
1:4.1.48-101:4.1.48-10+deb13u11:4.1.48-111:4.1.48-121:4.1.48-131:4.1.48-141:4.1.48-151:4.1.48-16
None known
netty
Debian:14
All versions, plus listed versions
1:4.1.48-101:4.1.48-111:4.1.48-121:4.1.48-131:4.1.48-141:4.1.48-151:4.1.48-16
None known
netty-tcnative
SUSE:Linux Enterprise Module for Development Tools 15 SP7
before 2.0.84-150200.3.51.1
2.0.84-150200.3.51.1
netty
SUSE:Linux Enterprise Module for Package Hub 15 SP7
before 4.1.138-150200.4.56.1
4.1.138-150200.4.56.1
netty-tcnative
SUSE:Linux Enterprise High Performance Computing 15 SP4-ESPOS
before 2.0.84-150200.3.51.1
2.0.84-150200.3.51.1
netty-tcnative
SUSE:Linux Enterprise High Performance Computing 15 SP4-LTSS
before 2.0.84-150200.3.51.1
2.0.84-150200.3.51.1
netty-tcnative
SUSE:Linux Enterprise High Performance Computing 15 SP5-ESPOS
before 2.0.84-150200.3.51.1
2.0.84-150200.3.51.1
netty-tcnative
SUSE:Linux Enterprise High Performance Computing 15 SP5-LTSS
before 2.0.84-150200.3.51.1
2.0.84-150200.3.51.1
netty-tcnative
SUSE:Linux Enterprise Server 15 SP4-LTSS
before 2.0.84-150200.3.51.1
2.0.84-150200.3.51.1
Show 14 moreShow less
Affected packages
PackageAffectedFixed
netty-tcnative
SUSE:Linux Enterprise Server 15 SP5-LTSS
before 2.0.84-150200.3.51.1
2.0.84-150200.3.51.1
netty-tcnative
SUSE:Linux Enterprise Server 15 SP6-LTSS
before 2.0.84-150200.3.51.1
2.0.84-150200.3.51.1
netty-tcnative
SUSE:Linux Enterprise Server for SAP Applications 15 SP4
before 2.0.84-150200.3.51.1
2.0.84-150200.3.51.1
netty-tcnative
SUSE:Linux Enterprise Server for SAP Applications 15 SP5
before 2.0.84-150200.3.51.1
2.0.84-150200.3.51.1
netty-tcnative
SUSE:Linux Enterprise Server for SAP Applications 15 SP6
before 2.0.84-150200.3.51.1
2.0.84-150200.3.51.1
netty
Ubuntu:Pro:14.04:LTS
All versions, plus listed versions
1:3.2.6.Final-21:3.2.6.Final-2+deb8u2build0.14.04.1~esm11:3.2.6.Final-2+deb8u2ubuntu0.1~esm1
None known
netty
Ubuntu:Pro:16.04:LTS
All versions, plus listed versions
1:3.2.6.Final-21:4.0.32-11:4.0.33-11:4.0.34-11:4.0.34-1ubuntu0.1~esm1
Show 4 moreShow less
1:4.0.34-1ubuntu0.1~esm21:4.0.34-1ubuntu0.1~esm31:4.0.34-1ubuntu0.1~esm41:4.0.34-1ubuntu0.1~esm5
None known
netty
Ubuntu:Pro:18.04:LTS
All versions, plus listed versions
1:4.1.7-41:4.1.7-4ubuntu0.1~esm11:4.1.7-4ubuntu0.11:4.1.7-4ubuntu0.1+esm11:4.1.7-4ubuntu0.1+esm2
Show 5 moreShow less
1:4.1.7-4ubuntu0.1+esm31:4.1.7-4ubuntu0.1+esm41:4.1.7-4ubuntu0.1+esm51:4.1.7-4ubuntu0.1+esm61:4.1.7-4ubuntu0.1+esm7
None known
netty
Ubuntu:Pro:20.04:LTS
All versions, plus listed versions
1:4.1.33-11:4.1.33-21:4.1.33-31:4.1.45-11:4.1.45-1ubuntu0.1~esm1
Show 5 moreShow less
1:4.1.45-1ubuntu0.1~esm21:4.1.45-1ubuntu0.1~esm31:4.1.45-1ubuntu0.1~esm41:4.1.45-1ubuntu0.1~esm61:4.1.45-1ubuntu0.1~esm7
None known
netty
Ubuntu:Pro:22.04:LTS
All versions, plus listed versions
1:4.1.48-41:4.1.48-4+deb11u1build0.22.04.11:4.1.48-4+deb11u2build0.22.04.11:4.1.48-4+deb11u2ubuntu0.1~esm11:4.1.48-4+deb11u2ubuntu0.1~esm2
Show 5 moreShow less
1:4.1.48-4+deb11u2ubuntu0.11:4.1.48-4+deb11u2ubuntu0.1+esm11:4.1.48-4+deb11u2ubuntu0.1+esm31:4.1.48-4+deb11u2ubuntu0.21:4.1.48-4+deb11u2ubuntu0.2+esm1
None known
netty
Ubuntu:Pro:24.04:LTS
All versions, plus listed versions
1:4.1.48-71:4.1.48-81:4.1.48-91:4.1.48-9ubuntu0.1~esm11:4.1.48-9ubuntu0.1~esm2
Show 6 moreShow less
1:4.1.48-9ubuntu0.11:4.1.48-9ubuntu0.1+esm11:4.1.48-9ubuntu0.1+esm31:4.1.48-9ubuntu0.21:4.1.48-9ubuntu0.2+esm11:4.1.48-9ubuntu0.2+esm2
None known
netty
Ubuntu:26.10
All versions, plus listed versions
1:4.1.48-161:4.1.48-16ubuntu1
None known
netty
Ubuntu:Pro:26.04:LTS
All versions, plus listed versions
1:4.1.48-101:4.1.48-111:4.1.48-121:4.1.48-131:4.1.48-141:4.1.48-161:4.1.48-16ubuntu0.1~esm2
None known
netty
openSUSE:Tumbleweed
before 4.1.138-1.1
4.1.138-1.1

History

History
RecordedChangedSources
first indexedCVE List, EUVD, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2026-76816 is a low vulnerability (CVSS 3.5) in Netty, published August 24, 2026. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.17%, the 6th percentile. Fixed in netty-tcnative 2.0.84-150200.3.51.1.

References

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