CVE-2021-27565Network attack vector

Remote denial of service via HTTP debugger hook

Published Aug 19, 2021 · Updated Aug 3, 2024

Denial of service in InterNiche NicheStack through 4.0.1 allows remote attackers to interrupt networking via an unexpected valid HTTP request. The HTTP request handler enters a miscoded wbs_loop() debugger hook when processing requests such as OPTIONS, creating an infinite loop. Any remote client able to reach the web server can trigger the loop and cause a networking outage; the record describes availability impact without data disclosure or modification.

CVSS severity7.5
High
EPSS probability2.59%
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 InterNiche NicheStack through 4.0.1 allows remote attackers to interrupt networking via an unexpected valid HTTP request. The HTTP request handler enters a miscoded wbs_loop() debugger hook when processing requests such as OPTIONS, creating an infinite loop. Any remote client able to reach the web server can trigger the loop and cause a networking outage; the record describes availability impact without data disclosure or modification.

The record

CVE
CVE-2021-27565
Published
Aug 19, 2021
Updated
Aug 3, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-835, T1499.002
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 19, 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?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

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 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-835Loop with Unreachable Exit Condition ('Infinite Loop')
T1499.002Service Exhaustion

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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