CVE-2021-30666

Improper Restriction of Operations within the Bounds of a Memory Buffer

CVSS 3.1 High 8.8Known exploited (CISA KEV)

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

Description

A buffer overflow issue was addressed with improved memory handling. This issue is fixed in iOS 12.5.3. Processing maliciously crafted web content may lead to arbitrary code execution. Apple is aware of a report that this issue may have been actively exploited..

Key data

CVSS 3.1 High 8.8

Score published by CISA-ADP in the CVE record.

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

Attack vector: Network
The vulnerable component can be reached over a network, possibly from the Internet.
Attack complexity: Low
No special conditions are needed. The attack can be repeated at will.
Privileges required: None
No account or privileges are needed.
User interaction: Required
A user has to do something first, such as opening a file or following a link.
Scope: Unchanged
The impact stays within the vulnerable component.
Confidentiality impact: High
Serious or total effect on the secrecy of data.
Integrity impact: High
Serious or total effect on the trustworthiness of data.
Availability impact: High
Serious or total effect on availability.

Metric	Value	What it means
Attack vector	Network	The vulnerable component can be reached over a network, possibly from the Internet.
Attack complexity	Low	No special conditions are needed. The attack can be repeated at will.
Privileges required	None	No account or privileges are needed.
User interaction	Required	A user has to do something first, such as opening a file or following a link.
Scope	Unchanged	The impact stays within the vulnerable component.
Confidentiality impact	High	Serious or total effect on the secrecy of data.
Integrity impact	High	Serious or total effect on the trustworthiness of data.
Availability impact	High	Serious or total effect on availability.

CVSS is owned and managed by FIRST.Org, Inc. (FIRST) and is used by permission. Each CVSS score on this site is shown together with its vector string, as published in the CVE record by the source named next to it. Learn more at first.org/cvss.

EPSS

Exploit Prediction Scoring System by FIRST: an estimate of the probability that exploitation activity will be observed in the next 30 days.

Score: 0.02966 (3.0% probability)
Percentile: 87.3%
Scores of: Nov 10, 2026
Model: v2026.06.15

CISA Known Exploited Vulnerabilities

This CVE is listed in the CISA KEV catalog.

Name in the catalog: Apple iOS WebKit Buffer Overflow Vulnerability
Added to the catalog: Nov 3, 2021
Federal due date: Nov 17, 2021

CISA assessment as of Jan 29, 2025

Stakeholder-Specific Vulnerability Categorization (SSVC) decision points added by CISA.

Exploitation: Recorded by CISA as active
Automatable: no
Technical impact: total

Weakness (CWE)

CWE catalog version 5.0.

CWE-119Improper Restriction of Operations within the Bounds of a Memory Buffer

Affected products

Products listed in the CVE record, as the CNA published them.

Apple iOS
- affected: unspecified up to before 12.5

References

Links listed in the CVE record. They lead to other sites, which CubePath does not control.

support.apple.com/en-us/HT212341

Timeline

ID reservedApr 13, 2021
Record publishedSep 8, 2021
Added to CISA KEVNov 3, 2021
Record last updatedOct 21, 2025

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Data from the CVE Program (MITRE), CISA KEV and FIRST EPSS. CVSS is owned by FIRST and used by permission. Not affiliated with or endorsed by MITRE, CISA or FIRST. Data as of Nov 10, 2026, 19:52 UTC. Sources and licenses