CVE-2019-20445Public exploitNetwork attack vector

HTTP request smuggling via conflicting length headers

Published Jan 29, 2020 · Updated Aug 5, 2024

HTTP request smuggling in Netty before 4.1.44 allows remote attackers to conceal requests behind conflicting message-length headers. HttpObjectDecoder accepts duplicate Content-Length fields or a Content-Length field combined with Transfer-Encoding instead of rejecting the ambiguous HTTP/1.1 message. Exploitation requires Netty and an HTTP intermediary to disagree on request boundaries, enabling front-end control bypass or cross-user request interference.

CVSS severity9.1
Critical
EPSS probability13.47%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

HTTP request smuggling in Netty before 4.1.44 allows remote attackers to conceal requests behind conflicting message-length headers. HttpObjectDecoder accepts duplicate Content-Length fields or a Content-Length field combined with Transfer-Encoding instead of rejecting the ambiguous HTTP/1.1 message. Exploitation requires Netty and an HTTP intermediary to disagree on request boundaries, enabling front-end control bypass or cross-user request interference.

The record

CVE
CVE-2019-20445
Published
Jan 29, 2020
Updated
Aug 5, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-444, CAPEC-33, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jan 29, 2020CVE publishedPublication date reported by the CVE source.
  2. Aug 5, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

9.1NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-444Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')
CAPEC-33HTTP Request Smuggling
T1190Exploit Public-Facing Application

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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