CVE & CISA-KEV Catalog

CVE-2021-21409

MEDIUMEPSS 91th pctl
5.9
CVSS v3
NVD

Description

Netty is an open-source, asynchronous event-driven network application framework for rapid development of maintainable high performance protocol servers & clients. In Netty (io.netty:netty-codec-http2) before version 4.1.61.Final there is a vulnerability that enables request smuggling. The content-length header is not correctly validated if the request only uses a single Http2HeaderFrame with the endStream set to to true. This could lead to request smuggling if the request is proxied to a remote peer and translated to HTTP/1.1. This is a followup of GHSA-wm47-8v5p-wjpj/CVE-2021-21295 which did miss to fix this one case. This was fixed as part of 4.1.61.Final.

CWE-444

How to fix

Remediation Available
nettyDebian
Fixed in:1:4.1.48-4CVE-2021-21409
Fixed in:1:4.1.48-4CVE-2021-21409
Fixed in:1:4.1.48-4CVE-2021-21409
Fixed in:1:4.1.48-4CVE-2021-21409
libnetty-javaUbuntu
Fixed in:1:4.0.34-1ubuntu0.1~esm1USN-6049-1
Fixed in:1:4.1.7-4ubuntu0.1+esm2USN-6049-1
Fixed in:1:4.1.45-1ubuntu0.1~esm1USN-6049-1
Fixed in:1:4.1.48-4+deb11u1build0.22.04.1USN-6049-1
Fixed in:1:4.1.48-5ubuntu0.1USN-6049-1
nettyUbuntu
Fixed in:1:4.0.34-1ubuntu0.1~esm1USN-6049-1
Fixed in:1:4.1.7-4ubuntu0.1+esm2USN-6049-1
Fixed in:1:4.1.45-1ubuntu0.1~esm1USN-6049-1
Fixed in:1:4.1.48-4+deb11u1build0.22.04.1USN-6049-1
Fixed in:1:4.1.48-5ubuntu0.1USN-6049-1

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Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.

CVSS v3 Vector

Exploitability

Attack VectorNetwork
Attack ComplexityHigh
Privileges RequiredNone
User InteractionNone
ScopeUnchanged

Impact

ConfidentialityNone
IntegrityHigh
AvailabilityNone

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

Exploit Intelligence

4.93%probability of exploitation in 30 days
91stpercentile

High risk: more likely to be exploited than 91% of all known CVEs.

References

Related Vulnerabilities

Other CWE-444 vulnerabilities, ordered by exploit likelihood. View all

CVESeverityCVSSEPSSExploitedFix
CVE-2022-22536Critical10.098%KEV-
CVE-2025-61884High7.598%KEV + Ransom-
CVE-2020-9490High7.590%-Fix
CVE-2023-41265Critical9.684%KEV + Ransom-
CVE-2023-25690Critical9.884%-Fix
CVE-2022-32214Medium6.581%-Fix

Common questions

How do I fix CVE-2021-21409?

Published advisories record a fix for 3 affected products. The "How to fix" section on this page lists the fixed version and source advisory for each one, so apply the entry matching what you actually run.

Is CVE-2021-21409 being actively exploited?

Not that we know of. CVE-2021-21409 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 4.9% is the estimated probability that it will be exploited in the next 30 days. That is higher than 91% of all scored CVEs.

How severe is CVE-2021-21409?

CVE-2021-21409 has a CVSS v3 base score of 5.9, rated medium. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.

What does CVE-2021-21409 affect?

Published advisories record a fix for netty (Debian), libnetty-java (Ubuntu), netty (Ubuntu). Only products with a sourced advisory are listed, so treat this as what we can cite rather than a complete inventory.

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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2024-11-21.