CVE-2021-37147Network attack vector

Unauthenticated request smuggling via LF-only headers

Published Nov 3, 2021 · Updated Aug 4, 2024

HTTP request smuggling in Apache Traffic Server 8.0.0 through 8.1.2 and 9.0.0 through 9.1.0 allows remote attackers to inject requests. The MIME header parser marks LF-terminated fields as raw-printable, so forwarding preserves a lone LF instead of emitting the required CRLF delimiter. No authentication or user interaction is required; inconsistent parsing by Traffic Server and another HTTP hop can route an injected request as a separate message.

CVSS severity7.5
High
EPSS probability2.52%
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 Apache Traffic Server 8.0.0 through 8.1.2 and 9.0.0 through 9.1.0 allows remote attackers to inject requests. The MIME header parser marks LF-terminated fields as raw-printable, so forwarding preserves a lone LF instead of emitting the required CRLF delimiter. No authentication or user interaction is required; inconsistent parsing by Traffic Server and another HTTP hop can route an injected request as a separate message.

The record

CVE
CVE-2021-37147
Published
Nov 3, 2021
Updated
Aug 4, 2024
Vendor
The Apache Software Foundation
Product
Apache Traffic Server
Classifications
CWE-444, CWE-20, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Nov 3, 2021CVE 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

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Is a vulnerable build present?

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

  1. Affected versionversion=8.0.0 to 8.1.2 and 9.0.0 to 9.1.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

The Apache Software Foundation · Apache Traffic Serverversion=8.0.0 to 8.1.2 and 9.0.0 to 9.1.0

Published CVSS scores

5.0NIST NVDAV:N/AC:L/Au:N/C:N/I:P/A:N
7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/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.

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')
CWE-20Improper Input Validation
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

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Your stack

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