CVE-2019-20444Public exploitNetwork attack vector

Unauthenticated request smuggling via colonless HTTP headers

Published Jan 29, 2020 · Updated Jul 1, 2025

HTTP request smuggling in Netty before 4.1.44 allows remote attackers to desynchronize HTTP parsing with a malformed header. HttpObjectDecoder's splitHeader method accepts a header line with no colon and treats it as an invalid continuation, allowing HTTP components to disagree about request boundaries. Exploitation requires another HTTP parser that handles the colonless line differently, enabling unauthorized requests or data access without authentication.

CVSS severity9.1
Critical
EPSS probability8.91%
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 desynchronize HTTP parsing with a malformed header. HttpObjectDecoder's splitHeader method accepts a header line with no colon and treats it as an invalid continuation, allowing HTTP components to disagree about request boundaries. Exploitation requires another HTTP parser that handles the colonless line differently, enabling unauthorized requests or data access without authentication.

The record

CVE
CVE-2019-20444
Published
Jan 29, 2020
Updated
Jul 1, 2025
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. Jul 1, 2025Record 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

9.1GitHub Advisory DatabaseCVSS: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 9, 2026Sep 15, 2026
Latest reporting daySep 15, 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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