CVE-2021-1821Network attack vector

System denial of service via Networking state mishandling

Published Oct 28, 2021 · Updated Aug 3, 2024

A Networking logic flaw in Apple macOS before 11.5 allows remote attackers to cause a system denial of service via a malicious webpage. Apple has disclosed only that Networking mishandles state; no public patch detail identifies the faulty state transition or request field. Exploitation requires user interaction to visit attacker-controlled web content, and the reported consequence is limited to system availability.

CVSS severity6.5
Medium
EPSS probability0.66%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

A Networking logic flaw in Apple macOS before 11.5 allows remote attackers to cause a system denial of service via a malicious webpage. Apple has disclosed only that Networking mishandles state; no public patch detail identifies the faulty state transition or request field. Exploitation requires user interaction to visit attacker-controlled web content, and the reported consequence is limited to system availability.

The record

CVE
CVE-2021-1821
Published
Oct 28, 2021
Updated
Aug 3, 2024
Vendor
Apple
Product
macOS
Classifications
Unavailable
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Oct 28, 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

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=unspecified <11.5
  2. Affected versionversion=unspecified <7.6

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Apple · macOSversion=unspecified <11.5; version=unspecified <7.6

Published CVSS scores

6.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
7.1NIST NVDAV:N/AC:M/Au:N/C:N/I:N/A:C

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

No sourced classifications are available.

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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