NVD / CVE Program· CNA GitHub_M

CVE-2026-56819: Netty: HTTP/2 decompression leaks ByteBuf reference count when the decompressor channel is already closed (Direct memory leak / OOM DoS)

HighCVSS 7.5 · v3.1—Proof of concept Fix available

Noroxi assessment

Priority: Monitor (action score 30/100)

Public proof-of-concept code exists (GitHub); there is no record of exploitation in the wild.
Probability of exploitation in the next 30 days: 0.66% (FIRST EPSS); higher than 52.2% of all records.
Anyone who can reach it over the internet can trigger it. No account or password is required. No user action is required. No special conditions are required; it is repeatable.
According to CISA the attack is automatable: targets can be found by mass scanning.
Fixed version: io.netty:netty-codec-http2 (Maven) 4.1.136.Final, 4.2.16.Final; netty (openSUSE:Tumbleweed) 4.1.136-1.1; netty-tcnative (SUSE:Linux Enterprise Module for Development Tools 15 SP7) 2.0.80-150200.3.48.1.

Low priority for now. Upgrade to io.netty:netty-codec-http2 (Maven) 4.1.136.Final, 4.2.16.Final; netty (openSUSE:Tumbleweed) 4.1.136-1.1; netty-tcnative (SUSE:Linux Enterprise Module for Development Tools 15 SP7) 2.0.80-150200.3.48.1 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 a network application framework for development of protocol servers and clients. In versions 4.2.0.Final through 4.2.15.Final and 4.1.0.Final through 4.1.135.Final, a remote unauthenticated peer can leak one direct `ByteBuf` per HTTP/2 `DATA` frame in applications that enable HTTP/2 content decompression via `DelegatingDecompressorFrameListener`. When a `DATA` frame is processed for a stream whose decompressor has already been closed, `Http2Decompressor.decompress(...)` calls `decompressor.writeInbound(data.retain())` and does not release the retained buffer on the error path, eventually exhausting direct memory and crashing the JVM. This issue is fixed in versions 4.1.136.Final and 4.2.16.Final.

Published: Jul 21, 2026
Updated: Jul 30, 2026
EPSS: 0.6% · 52th percentile
CWE: CWE-400

Report tools

JSON

Action score

Monitor

Low priority for now.

CVSS: 30 / 40 · 7.5 / 10
CISA KEV: 0 / 30 · Not listed
EPSS: 0 / 30 · 0.6%

CISA SSVC decision

Exploitation: proof of concept
Automatable: yes
Technical impact: partial

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD: —
CNA · GitHub_M: 7.5; 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
Proof of concept exists, no weaponized module
A fix has been released

If any of these changes, we'll tell you in the daily email digest.

Is your version affected? Check it

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 help

Affected 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.

Vendor	Product	CPE
netty	netty	cpe:2.3:a:netty:netty

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

netty netty4.1.0 and later · before 4.1.136
netty netty4.2.0 and later · before 4.2.16

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, < 4.2.16.Final, >= 4.1.0.Final, < 4.1.136.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	—
Maven	io.netty:netty-codec-http2	from 4.1.0.Final · before 4.1.136.Final	4.1.136.Final
Maven	io.netty:netty-codec-http2	from 4.2.0 · before 4.2.16.Final	4.2.16.Final
openSUSE:Tumbleweed	netty	before 4.1.136-1.1	4.1.136-1.1
SUSE:Linux Enterprise Module for Development Tools 15 SP7	netty-tcnative	before 2.0.80-150200.3.48.1	2.0.80-150200.3.48.1
SUSE:Linux Enterprise Module for Package Hub 15 SP7	netty	before 4.1.136-150200.4.53.1	4.1.136-150200.4.53.1

Same product

netty: all records

Other highest-scoring records for the same primary product.

CVE-2026-47691Netty has Insufficient Bailiwick Validation for NS Records
40Plan
CVE-2026-45674Netty Vulnerable to DNS Cache Poisoning via Missing Bailiwick Checks in CNAME Records
40Plan
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…
40Plan

Published before and after this one in the same product

← EarlierCVE-2026-56816Jul 21, 2026 · Netty: Memory Exhaustion via HTTP/3 Reserved Frame Types
30Monitor
← EarlierCVE-2026-56817Jul 21, 2026 · Netty: XML External Entity (XXE) injection via unconfigured XML factory when DTD and entity processing are enabled
33Monitor
Later →CVE-2026-56820Jul 21, 2026 · Netty: Missing CertificateID Validation in OCSP Response Allows Replay Attacks
36Monitor

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
Maven:io.netty:netty-codec-http2	4.1.136.Final	Package registry (OSV)
Maven:io.netty:netty-codec-http2	4.2.16.Final	Package registry (OSV)
opensuse:netty	4.1.136-1.1 · openSUSE:Tumbleweed	Package registry (OSV)
suse:netty	4.1.136-150200.4.53.1 · SUSE:Linux Enterprise Module for Package Hub 15 SP7	Package registry (OSV)
suse:netty-tcnative	2.0.80-150200.3.48.1 · SUSE:Linux Enterprise Module for Development Tools 15 SP7	Package registry (OSV)

Exploit status

Proof of concept available

A public proof of concept or detection signature exists. Exploit knowledge is out there; don't delay patching.

Evidence

Proof-of-concept repository on GitHub ×1

Noroxi does not host or link to exploit code. Metasploit module names and Nuclei template ids are shown (names, not code); Exploit-DB entries and PoC repositories are given as counts only.

Public exploit evidence
Source	Kind	Date
Proof-of-concept repository on GitHub	stars:0	2026-09-05

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.

PublishedJul 21, 2026
First PoCSep 5, 2026+45 d
TodayNov 12, 2026+114 d

EPSS, last 120 days

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 researchers

Finders, 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-2026-558510 days apartNetty codec-haproxy: Signed-Byte Sentinel Collision in HAProxyMessageDecoder Leads to Unbounded Memory Exhaustion
34Monitor
CVE-2026-567450 days apartNetty SpdyHttpDecoder: ByteBuf Reference Leak on RST_STREAM Leads to Native Memory Exhaustion
34Monitor
CVE-2026-10066167 days apartNetty HTTP/3 QPACK Prefixed Integer DoS via Unbounded Accumulation
34Monitor
CVE-2026-10066267 days apartNetty HTTP/3 QPACK encoder-stream unbounded memory exhaustion DoS
34Monitor
CVE-2026-568160 days apartNetty: Memory Exhaustion via HTTP/3 Reserved Frame Types
30Monitor
CVE-2026-558311 days apartNetty SPDY SETTINGS frame count materializes unbounded settings map
30Monitor

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

Anyone who can reach it over the internet can trigger it.
No account or password is required.
No user action is required.
No special conditions are required; it is repeatable.

If successful

Confidentiality: none
Integrity: none
Availability: high · the service can be disrupted

Attack vector: Network
Attack complexity: Low
Privileges required: None
User interaction: None
Scope: Unchanged
Confidentiality impact: None
Integrity impact: None
Availability impact: High

Weakness class (CWE)

CWE-400 · Uncontrolled Resource Consumption

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

nvd-secondary

Root cause

Code that parses nested structures sets no depth or size limit. A small input can turn into a disproportionate processing load.

The bug in code

The whole CWE-400 class

A representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.

Vulnerable

1function expand(node) {
2  return node.children.map(expand);
3}

Fixed

1const MAX_DEPTH = 32;
2function expand(node, depth = 0) {
3  if (depth > MAX_DEPTH) throw new Error("too deep");
4  return node.children.map((c) => expand(c, depth + 1));
5}