CVE-2021-27737Network attack vector

Remote service interruption

Published May 14, 2021 · Updated Aug 3, 2024

Denial of service in Apache Traffic Server 9.0.0 allows remote attackers to interrupt service through the experimental Slicer plugin. Apache has not published the faulty Slicer code path, triggering request shape, or whether the interruption is a crash, hang, or another failure mode. Exposure requires version 9.0.0 with the experimental plugin configured on a reachable remap rule; the documented consequence is limited to service availability.

CVSS severity7.5
High
EPSS probability3.80%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in Apache Traffic Server 9.0.0 allows remote attackers to interrupt service through the experimental Slicer plugin. Apache has not published the faulty Slicer code path, triggering request shape, or whether the interruption is a crash, hang, or another failure mode. Exposure requires version 9.0.0 with the experimental plugin configured on a reachable remap rule; the documented consequence is limited to service availability.

The record

CVE
CVE-2021-27737
Published
May 14, 2021
Updated
Aug 3, 2024
Vendor
The Apache Software Foundation
Product
Apache Traffic Server
Classifications
T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 14, 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 9.0.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

The Apache Software Foundation · Apache Traffic Serverversion=Apache Traffic Server 9.0.0

Published CVSS scores

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

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

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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