CVE-2021-30666Known exploitationNetwork attack vector

Arbitrary code execution via WebKit buffer overflow

Published Sep 8, 2021 · Updated Oct 21, 2025

Buffer overflow in WebKit in Apple iOS before 12.5.3 allows remote attackers to execute arbitrary code via crafted web content. Apple identifies the locus only as WebKit and states that its memory handling permits a buffer overflow; no function or parsing path is public. The target must process the crafted content, so delivery alone is insufficient; Apple reports active exploitation.

CVSS severity8.8
High
EPSS probability3.00%
Next 30 days · Sep 16, 2026
Known exploitationReported
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Buffer overflow in WebKit in Apple iOS before 12.5.3 allows remote attackers to execute arbitrary code via crafted web content. Apple identifies the locus only as WebKit and states that its memory handling permits a buffer overflow; no function or parsing path is public. The target must process the crafted content, so delivery alone is insufficient; Apple reports active exploitation.

The record

CVE
CVE-2021-30666
Published
Sep 8, 2021
Updated
Oct 21, 2025
Vendor
Apple
Product
iOS
Classifications
CWE-119, T1203, T1189
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 8, 2021CVE publishedPublication date reported by the CVE source.
  2. Oct 21, 2025Record 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=unspecified <12.5

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Apple · iOSversion=unspecified <12.5

Published CVSS scores

8.8CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
6.8NIST NVDAV:N/AC:M/Au:N/C:P/I:P/A:P
8.8NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/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 exploitationReported
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-119Improper Restriction of Operations within the Bounds of a Memory Buffer
T1203Exploitation for Client Execution
T1189Drive-by Compromise

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.

Reported exploitation

Technologies

Your stack

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Your stack

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