CVE-2020-5207Network attack vector

Request smuggling via unchecked conflicting body lengths

Published Jan 27, 2020 · Updated Aug 4, 2024

HTTP request smuggling in JetBrains Ktor before 1.3.0 allows remote attackers to desynchronize proxy and backend request parsing. The CIO body decoder accepted chunked encoding without comparing decoded bytes with Content-Length, leaving different message boundaries across the proxy and backend. Exploitation requires a proxy that interprets conflicting headers or lone line-feed separators differently, enabling unauthorized backend requests or response mix-ups.

CVSS severity7.5
High
EPSS probability0.76%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

HTTP request smuggling in JetBrains Ktor before 1.3.0 allows remote attackers to desynchronize proxy and backend request parsing. The CIO body decoder accepted chunked encoding without comparing decoded bytes with Content-Length, leaving different message boundaries across the proxy and backend. Exploitation requires a proxy that interprets conflicting headers or lone line-feed separators differently, enabling unauthorized backend requests or response mix-ups.

The record

CVE
CVE-2020-5207
Published
Jan 27, 2020
Updated
Aug 4, 2024
Vendor
JetBrains
Product
Ktor
Classifications
CWE-444, CAPEC-33, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jan 27, 2020CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 1.3.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

JetBrains · Ktorversion=< 1.3.0

Published CVSS scores

7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
5.4GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N
5.0NIST NVDAV:N/AC:L/Au:N/C:N/I:P/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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

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 exploitUnconfirmed

Weakness, pattern, technique

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

Public exploit references

No public exploit references are available in this record.

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

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo