CVE-2021-44040Network attack vector

Request smuggling via permissive URL parsing

Published Mar 23, 2022 · Updated Aug 4, 2024

Improper request-line validation in Apache Traffic Server 8.0.0 through 8.1.3 and 9.0.0 through 9.1.1 allows remote attackers to smuggle requests. The URL parser accepts whitespace and non-printable characters because proxy.config.http.strict_uri_parsing defaults to disabled. Unauthenticated network access to a proxy listener is sufficient; crafted request boundaries can be interpreted differently across HTTP intermediaries.

CVSS severity7.5
High
EPSS probability1.99%
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

Improper request-line validation in Apache Traffic Server 8.0.0 through 8.1.3 and 9.0.0 through 9.1.1 allows remote attackers to smuggle requests. The URL parser accepts whitespace and non-printable characters because proxy.config.http.strict_uri_parsing defaults to disabled. Unauthenticated network access to a proxy listener is sufficient; crafted request boundaries can be interpreted differently across HTTP intermediaries.

The record

CVE
CVE-2021-44040
Published
Mar 23, 2022
Updated
Aug 4, 2024
Vendor
The Apache Software Foundation
Product
Apache Traffic Server
Classifications
CWE-20, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 23, 2022CVE 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=8.0.0 to 8.1.3 and 9.0.0 to 9.1.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

The Apache Software Foundation · Apache Traffic Serverversion=8.0.0 to 8.1.3 and 9.0.0 to 9.1.1

Published CVSS scores

7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
5.0NIST 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-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

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