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CVE-2026-56817

Netty XML external entity (XXE)

9.8 CRITICALEPSS 0.69%
  1. Published21 Jul 2026

Description

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, any caller that can deliver bytes to a Netty channel pipeline containing `XmlDecoder` can send XML with a `DOCTYPE` declaration to an `AsyncXMLInputFactory` instantiated with no security configuration, leaving DTD and entity handling active depending on Aalto XML async parser behavior and creating conditional XML external entity risk. This issue is fixed in versions 4.1.136.Final and 4.2.16.Final.

CVSS 3.1 breakdown

Attack vectorNetwork
Attack complexityLow
Privileges requiredNone
User interactionNone
ScopeUnchanged
ConfidentialityHigh
IntegrityHigh
AvailabilityHigh
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected products

Netty≥ 4.1.0 < 4.1.136 · ≥ 4.2.0 < 4.2.16

Remediation

Fixed in
Netty≥ 4.1.136

References

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Frequently asked

Is CVE-2026-56817 being actively exploited?

CVE-2026-56817 is not in the CISA KEV catalog. Its EPSS exploit probability is 0.69%.

How severe is CVE-2026-56817?

CVE-2026-56817 has a CVSS 3.1 base score of 9.8, rated critical. EPSS estimates a 0.69% probability of exploitation.

Which products are affected by CVE-2026-56817?

Affected products include Netty.

How do I fix CVE-2026-56817?

Upgrade affected software to a fixed version, for example Netty 4.1.136 or later, then confirm no affected versions remain in your inventory.

How Secuno handles this

Secuno correlates vulnerabilities like CVE-2026-56817 against the real software inventory on every managed device, every day. Rather than a static severity, each match is scored in context: exploit availability, EPSS, the asset's exposure, and business criticality decide where it lands in the queue. If an affected version is present anywhere across your portfolio, it surfaces automatically with a prioritised remediation path.

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Data from the NVD, CISA KEV catalog and FIRST EPSS. CVSS 3.1 base score shown where available.