CVE Intelligence
Medium Injection

CVE-2021-21409 — Possible request smuggling in HTTP/2 due missing validation of content-length

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.

Published Mar 30, 2021 · Updated Oct 13, 2026 · Sources: NIST National Vulnerability Database, CVE Program (cve.org) e CISA ADP · CNA: GitHub_M

Who exploits it and how urgent it is

A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.

No exploitation signal in the sources consulted so far.
How the score was calculated
  • EPSS 4.9% (30-day exploitation probability)+14
  • Technical severity (medium)+3
  • Automatable exploitation (SSVC)+3

The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.

Exploitation
Not confirmed
Not in CISA KEV — an absence of record, not proof it is unexploited.
EPSS FIRST
4.94%
ahead of 92% of scored CVEs · Oct 15, 2026
Affects
Debian
Debian Linux and 17 more
CVSS base
5.9
Medium · 3 source(s)

CISA SSVC assessment CISA

Three decision points CISA publishes for the CVEs it assesses (SSVC 2.0.3). A stakeholder decision, not a severity score.

Exploitation
None
none · proof-of-concept · active
Automatable
Yes
can an attacker script the kill-chain steps
Technical impact
Partial
partial · total control of the vulnerable component

Remediation

Fixes and mitigations documented by the sources — linked to the original advisory.

  • Documented patch — github.com (NIST National Vulnerability Database)
  • Documented patch — www.oracle.com (NIST National Vulnerability Database)
  • Documented patch — www.oracle.com (NIST National Vulnerability Database)
  • Documented patch — www.oracle.com (NIST National Vulnerability Database)
  • Documented patch — www.oracle.com (NIST National Vulnerability Database)

First 24 hours

Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.

  1. Identify exposed assets running the affected vendor/product/version combinations (Debian Debian Linux, Netapp Oncommand Api Services, Netapp Oncommand Workflow Automation…).
  2. The attack is network-based and needs no privileges: restrict exposure (ACLs, VPN, WAF) until patched.
  3. Apply the fixed version or the patch documented under Remediation.
  4. EPSS ahead of 92% of scored CVEs: prioritize it in the patch queue.
  5. Search available logs for exploit probes matching the vulnerability class (injection), errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

VendorProductVersionsStatusSource
Debian Debian Linux version 10.0 Vulnerable NIST National Vulnerability Database
Netapp Oncommand Api Services versions not specified by the source Vulnerable NIST National Vulnerability Database
Netapp Oncommand Workflow Automation versions not specified by the source Vulnerable NIST National Vulnerability Database
Netty Netty < 4.1.61 Vulnerable NIST National Vulnerability Database
Netty Netty version < 4.1.61.Final Vulnerable CVE Program (cve.org) e CISA ADP
Oracle Banking Corporate Lending Process Management version 14.3.0version 14.5.0version 14.2.0 Vulnerable NIST National Vulnerability Database
Oracle Banking Credit Facilities Process Management version 14.2.0version 14.3.0version 14.5.0 Vulnerable NIST National Vulnerability Database
Oracle Banking Trade Finance Process Management version 14.2.0version 14.3.0version 14.5.0 Vulnerable NIST National Vulnerability Database
Oracle Coherence version 12.2.1.4.0version 14.1.1.0.0 Vulnerable NIST National Vulnerability Database
Oracle Communications Brm - Elastic Charging Engine version 12.0.0.3 Vulnerable NIST National Vulnerability Database
Oracle Communications Cloud Native Core Console version 1.7.0 Vulnerable NIST National Vulnerability Database
Oracle Communications Cloud Native Core Policy version 1.14.0 Vulnerable NIST National Vulnerability Database
Oracle Communications Design Studio version 7.4.2.0.0 Vulnerable NIST National Vulnerability Database
Oracle Communications Messaging Server version 8.1 Vulnerable NIST National Vulnerability Database
Oracle Helidon version 2.4.0version 1.4.10 Vulnerable NIST National Vulnerability Database
Oracle Jd Edwards Enterpriseone Tools < 9.2.6.3 Vulnerable NIST National Vulnerability Database
Oracle Nosql Database < 21.1.12 Vulnerable NIST National Vulnerability Database
Oracle Primavera Gateway ≥ 19.12.0 and ≤ 19.12.10≥ 18.8.0 and ≤ 18.8.11≥ 17.12.0 and ≤ 17.12.11 Vulnerable NIST National Vulnerability Database
Quarkus Quarkus ≤ 1.13.7 Vulnerable NIST National Vulnerability Database

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

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

Every base score collected

Sources score independently and may disagree; each row says who scored it and under which version.

ScoreVersionSeverityExpl.ImpactScored by
5.9 CVSS 3.1 Medium 2.2 3.6 security-advisories@github.com via NIST National Vulnerability Database
5.9 CVSS 3.1 Medium 2.2 3.6 nvd@nist.gov via NIST National Vulnerability Database
5.9 CVSS 3.1 Medium — — GitHub_M via CVE Program (cve.org) e CISA ADP
4.3 CVSS 2.0 Medium 8.6 2.9 nvd@nist.gov via NIST National Vulnerability Database
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N (score shown at the top: nvd@nist.gov)

Weakness MITRE

Weakness class according to MITRE’s CWE catalog.

CWE-444 · HTTP Request Smuggling

Other CVEs with this weakness →

EPSS over time FIRST

Oct 13, 2026 → Oct 15, 2026 · 3 reading(s) · max 4.94%

Detection

Read off the CVSS vector and the weakness class. Starting points, not tested rules.

  • Prioritize edge telemetry for the network-reachable component (proxy, WAF, IDS/IPS).
  • Look for parameters with command/query metacharacters and unexpected child processes of the service.
web/proxy/WAF logsnetwork IDS/IPSapplication logsendpoint telemetry (EDR)

Timeline

What happened to this CVE, newest first.

  • 2026
  • Affected products added · netty/netty
    Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
  • SSVC assessment updated
    Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
  • Record published
    Oct 13, 2026
  • Fix documented
    Oct 13, 2026 · NIST National Vulnerability Database
  • CVSS changed · 5.9
    Oct 13, 2026 · NIST National Vulnerability Database
  • Source status changed · → Modified
    Oct 13, 2026 · NIST National Vulnerability Database
  • Record created in this database
    Oct 13, 2026 · NIST National Vulnerability Database
  • 2021
  • CVE published
    Mar 30, 2021 · GitHub_M

Source activity

Repeated readings are counted rather than listed.

  • 1× Official description updated · Oct 13, 2026 – Oct 13, 2026

References

59 on the record

Elsewhere on this site

Debian
every CVE for this vendor
Injection
same class
CWE-444
other pages naming this weakness

Related CVEs (same products)

  • CVE-2026-100663 Netty HTTP/1 CONNECT authority-form mistranslated to malformed HTTP/3 19d
  • CVE-2026-100666 Netty 4.2.0 through 4.2.16 Response Desynchronization via HttpServerCodec 19d
  • CVE-2026-100665 Netty 4.2.11 through 4.2.17 QUIC Hostname Verification Bypass 19d
  • CVE-2026-100664 Netty 4.2.2 through 4.2.17 HTTP/1 Host Header Authority Confusion 19d
  • CVE-2026-100662 Netty HTTP/3 QPACK encoder-stream unbounded memory exhaustion DoS 19d
  • CVE-2026-100661 Netty HTTP/3 QPACK Prefixed Integer DoS via Unbounded Accumulation 19d

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

  • No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
  • No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
  • No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record

Text assembled only from the fields above — no additional claims.

What should defenders know first?

CVE-2021-21409 is "Possible request smuggling in HTTP/2 due missing validation of content-length", rated Medium. It affects Debian Linux (Debian); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 5.9 describes technical severity. EPSS 4.94% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.

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