CVE-2026-76816: Netty: MQTT Topic Name and Client ID Validation Bypass
Noroxi assessment
Priority: Monitor (action score 14/100)
- The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
- Probability of exploitation in the next 30 days: 0.17% (FIRST EPSS).
- Someone on the same network segment can trigger it. A low-privileged account is enough. No user action is required. No special conditions are required; it is repeatable.
- Fixed version: netty (openSUSE:Tumbleweed) 4.1.138-1.1; netty-tcnative (SUSE:Linux Enterprise Module for Development Tools 15 SP7) 2.0.84-150200.3.51.1; netty (SUSE:Linux Enterprise Module for Package Hub 15 SP7) 4.1.138-150200.4.56.1.
Low priority for now. Upgrade to netty (openSUSE:Tumbleweed) 4.1.138-1.1; netty-tcnative (SUSE:Linux Enterprise Module for Development Tools 15 SP7) 2.0.84-150200.3.51.1; netty (SUSE:Linux Enterprise Module for Package Hub 15 SP7) 4.1.138-150200.4.56.1 or later.
Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it
Primary sources: NVD · CVE.org · FIRST EPSS
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.
- Published
- Aug 24, 2026
- Updated
- Oct 12, 2026
- EPSS
- 0.1% · 6th percentile
- CWE
- CWE-20
Report tools
Action score
14
Monitor
Low priority for now.
- CVSS
- 14 / 40 · 3.5 / 10
- CISA KEV
- 0 / 30 · Not listed
- EPSS
- 0 / 30 · 0.1%
CISA SSVC decision
- Exploitation
- none
- Automatable
- no
- Technical impact
- partial
Vulnrichment: CISA's decision-tree inputs.
CNA vs NVD score
- NVD
- —
- CNA · GitHub_M
- 3.5
- NVD has not scored this yet; the score shown is the CNA’s.
The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.
Get told when this record changes
- Not in KEV: no record of exploitation in the wild
- No public exploit code on record
- A fix has been released
If any of these changes, we'll tell you in the daily email digest.
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Noroxi analysis
What does it mean in your environment?
The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.
We use this product, ask for helpAffected systems
Is your version affected?
Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.
—
Versions reported by the vendor
Affected version ranges reported by the assigning authority (GitHub_M). Independent of NVD's CPE analysis and usually ahead of it.
netty netty
- >= 4.2.0.Final, < 4.1.137.Final, < 4.1.137.Finalaffected
Package-level exposure
OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.
| Ecosystem | Package | Affected range | Fix |
|---|---|---|---|
| Debian:12 | netty | from 0 | — |
| openSUSE:Tumbleweed | netty | before 4.1.138-1.1 | 4.1.138-1.1 |
| SUSE:Linux Enterprise Module for Development Tools 15 SP7 | netty-tcnative | before 2.0.84-150200.3.51.1 | 2.0.84-150200.3.51.1 |
| SUSE:Linux Enterprise Module for Package Hub 15 SP7 | netty | before 4.1.138-150200.4.56.1 | 4.1.138-150200.4.56.1 |
Same product
netty: all recordsOther highest-scoring records for the same primary product.
- CVE-2026-47691Netty has Insufficient Bailiwick Validation for NS Records40Plan
- CVE-2026-45674Netty Vulnerable to DNS Cache Poisoning via Missing Bailiwick Checks in CNAME Records40Plan
- CVE-2019-20445HttpObjectDecoder.java in Netty before 4.1.44 allows a Content-Length header to be accompanied by a second Content-Length header, or by a Tr40Plan
Published before and after this one in the same product
- ← EarlierCVE-2026-62243Aug 22, 2026 · Netty 4.2.0 through 4.2.16 TLS Hostname Verification Bypass34Monitor
- ← EarlierCVE-2026-62380Aug 22, 2026 · Netty before 4.2.16.Final SOCKS Proxy Null Byte Injection25Monitor
- Later →CVE-2026-89044Sep 10, 2026 · Netty 4.1.133.Final through 4.1.137.Final and 4.2.13.Final through 4.2.17.Final HTTP Request Smuggling via Transfer-Encoding27Monitor
Remediation
Which version to upgrade to
Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.
| Product / package | Fixed version | Source |
|---|---|---|
| opensuse:netty | 4.1.138-1.1 · openSUSE:Tumbleweed | Package registry (OSV) |
| suse:netty | 4.1.138-150200.4.56.1 · SUSE:Linux Enterprise Module for Package Hub 15 SP7 | Package registry (OSV) |
| suse:netty-tcnative | 2.0.84-150200.3.51.1 · SUSE:Linux Enterprise Module for Development Tools 15 SP7 | Package registry (OSV) |
Exploit status
No known public exploit
No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.
Research context
For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.
Timeline
From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.
No dated events beyond publication.
FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).
Patch and commit links
Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.
Credits
All researchersFinders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.
No credits in the CNA record.
Variant candidates
Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.
- CVE-2026-42579103 days apartNetty: DNS Codec Input Validation Bypass in Netty (Encoder + Decoder)36Monitor
- CVE-2026-10066333 days apartNetty HTTP/1 CONNECT authority-form mistranslated to malformed HTTP/334Monitor
- CVE-2026-10066433 days apartNetty 4.2.2 through 4.2.17 HTTP/1 Host Header Authority Confusion34Monitor
Chain candidates
An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.
—
Bug bounty scope
No known public program.
Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).
Technical details
Attack conditions
- Someone on the same network segment can trigger it.
- A low-privileged account is enough.
- No user action is required.
- No special conditions are required; it is repeatable.
If successful
- Confidentiality
- none
- Integrity
- low · data or configuration can be modified
- Availability
- none
- Attack vector
- Adjacent
- Attack complexity
- Low
- Privileges required
- Low
- User interaction
- None
- Scope
- Unchanged
- Confidentiality impact
- None
- Integrity impact
- Low
- Availability impact
- None
Weakness class (CWE)
CWE-20 · Improper Input ValidationCVSS vector
CVSS:3.1/AV:A/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N
nvd-secondary
Attack context
MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.
Attack patterns (CAPEC)
- Buffer Overflow via Environment VariablesCAPEC-10likelihood: High · High
- Server Side Include (SSI) InjectionCAPEC-101likelihood: High · High
- Cross Zone ScriptingCAPEC-104likelihood: Medium · High
- Command Line Execution through SQL InjectionCAPEC-108likelihood: Low · Very High
- Object Relational Mapping InjectionCAPEC-109likelihood: Low · High
- SQL Injection through SOAP Parameter TamperingCAPEC-110likelihood: High · Very High
- Double EncodingCAPEC-120likelihood: Low · Medium
- Subverting Environment Variable ValuesCAPEC-13likelihood: High · Very High
ATT&CK techniques
- Obfuscated Files or InformationT1027
- Masquerading: Invalid Code SignatureT1036.001
- Steal Web Session CookieT1539
- Subvert Trust Controls: Code SigningT1553.002
- Impair Defenses:Impair Command History LoggingT1562.003
- Hijack Execution Flow:Dynamic Linker HijackingT1574.006
- Hijack Execution Flow:Path Interception by PATH Environment VariableT1574.007
Change log
- Fix✗ → ✓
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References
Show all references (2 more)Show less
Vendor advisories and official records. Exploit/PoC links are deliberately left out.