CVE-2021-32567Network attack vector

Service interruption via closed-session frame rescheduling

Published Jun 30, 2021 · Updated Aug 3, 2024

Improper HTTP/2 input validation in affected Apache Traffic Server releases allows remote attackers to interrupt proxy service. Http2ClientSession::_should_do_something_else schedules periodic reenable work every 128 frames without excluding an already closed connection. An unauthenticated network client with access to an HTTP/2-enabled proxy port can keep closed-session processing active, denying availability to legitimate traffic.

CVSS severity7.5
High
EPSS probability2.45%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper HTTP/2 input validation in affected Apache Traffic Server releases allows remote attackers to interrupt proxy service. Http2ClientSession::_should_do_something_else schedules periodic reenable work every 128 frames without excluding an already closed connection. An unauthenticated network client with access to an HTTP/2-enabled proxy port can keep closed-session processing active, denying availability to legitimate traffic.

The record

CVE
CVE-2021-32567
Published
Jun 30, 2021
Updated
Aug 3, 2024
Vendor
The Apache Software Foundation
Product
Apache Traffic Server
Classifications
CWE-20, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 30, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 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=Apache Traffic Server 7.0.0 to 7.1.12, 8.0.0 to 8.1.1, 9.0.0 to 9.0.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

The Apache Software Foundation · Apache Traffic Serverversion=Apache Traffic Server 7.0.0 to 7.1.12, 8.0.0 to 8.1.1, 9.0.0 to 9.0.1

Published CVSS scores

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

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 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 exploitUnconfirmed

Weakness, pattern, technique

CWE-20Improper Input Validation
T1499.004Application or System Exploitation

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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