NVD / CVE Program· CNA GitHub_M

CVE-2026-56820: Netty: Missing CertificateID Validation in OCSP Response Allows Replay Attacks

Noroxi assessment

Priority: Monitor (action score 36/100)

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: 0.31% (FIRST EPSS).
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.
Fixed version: io.netty:netty-handler-ssl-ocsp (Maven) 4.2.16.Final, 4.1.136.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-handler-ssl-ocsp (Maven) 4.2.16.Final, 4.1.136.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 prior to 4.1.135.Final, `OcspClient` does not validate that the `CertificateID` in an OCSP response matches the requested `CertificateID`, which can lead to replay attack. `OcspClient.validateResponse` accepts a legitimately signed `GOOD` status response for an unrelated certificate issued by the same CA, allowing bypass of revocation checks for another certificate. This issue is fixed in versions 4.1.136.Final and 4.2.16.Final.

CriticalCVSS 9.1 · v3.1—No exploit Fix available

Published: Jul 21, 2026
Updated: Jul 30, 2026
EPSS: 0.3% · 24th percentile
CWE: CWE-295

Report tools

JSON

Action score

Monitor

Low priority for now.

CVSS: 36 / 40 · 9.1 / 10
CISA KEV: 0 / 30 · Not listed
EPSS: 0 / 30 · 0.3%

CISA SSVC decision

Exploitation: proof of concept
Automatable: no
Technical impact: total

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD: 9.1
CNA · GitHub_M: 7.4; 1.7 point gap

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

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

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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.

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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

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This vulnerability is about certificate validation or weak cryptography. The free SSL checker tests your certificate, enabled TLS versions and weak ciphers.

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Affected versions

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

netty nettybefore 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, < 4.1.136.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-handler-ssl-ocsp	from 4.2.0.Final · before 4.2.16.Final	4.2.16.Final
Maven	io.netty:netty-handler-ssl-ocsp	before 4.1.136.Final	4.1.136.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 Tr
40Plan

Published before and after this one in the same product

← EarlierCVE-2026-56817Jul 21, 2026 · Netty: XML External Entity (XXE) injection via unconfigured XML factory when DTD and entity processing are enabled
33Monitor
← EarlierCVE-2026-56819Jul 21, 2026 · Netty: HTTP/2 decompression leaks ByteBuf reference count when the decompressor channel is already closed (Direct memory leak / OOM DoS)
30Monitor
Later →CVE-2026-59921Jul 28, 2026 · Netty: CRLF Injection via Multipart Filename in Netty HttpPostRequestEncoder
26Monitor

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-handler-ssl-ocsp	4.1.136.Final	Package registry (OSV)
Maven:io.netty:netty-handler-ssl-ocsp	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

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.

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-2026-10066567 days apartNetty 4.2.11 through 4.2.17 QUIC Hostname Verification Bypass
34Monitor

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: high · data can be read
Integrity: high · data or configuration can be modified
Availability: none

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

Weakness class (CWE)

CWE-295 · Improper Certificate Validation

CVSS vector

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

nvd-primary

Root cause

A certificate validation error is silently swallowed instead of terminating the connection. Often, code added for a test environment makes its way into production.

The bug in code

The whole CWE-295 class

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

Vulnerable

kotlin

1override fun checkServerTrusted(chain: Array<X509Certificate>, type: String) {
2  // Left empty for the test environment
3}

Fixed

kotlin

1val client = OkHttpClient.Builder()
2  .certificatePinner(
3    CertificatePinner.Builder()
4      .add("api.sirius.example", "sha256/…")
5      .build()
6  ).build()

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)

ATT&CK techniques

—

Change log

Fix✗ → ✓Sep 28, 2026, 10:47 PM UTC

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References

github.com/netty/netty/commit/5b68c61f37aa4a3045cba624cbea239655c9003b

Show all references (3 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

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