Exploited vulnerability · CISA KEV

Is CVE-2021-1870 exploited? Yes: in CISA KEV since 3 Nov 2021

Gociux · Apple iOS, iPadOS, and macOS · data: CISA KEV, CVE record, FIRST EPSS

Yes. CVE-2021-1870, Apple iOS, iPadOS, and macOS WebKit Remote Code Execution Vulnerability, is being exploited in the wild. CISA added it to its Known Exploited Vulnerabilities catalog on 3 Nov 2021, 215 days after it was published. It affects Apple iOS, iPadOS, and macOS. If you run it, CISA's required action is: Apply updates per vendor instructions.

exploitedYesCISA KEV · 3 Nov 2021

ransomwareNot knownno confirmed use

EPSStop 10%more likely than most to be exploited

severity9.8CVSS 3.1 · critical

US federal due17 Nov 2021BOD 22-01 deadline

What it is

Apple iOS, iPadOS, and macOS WebKit contain an unspecified logic vulnerability that allows a remote attacker to execute code. This vulnerability could impact HTML parsers that use WebKit, including but not limited to Apple Safari and non-Apple products which rely on WebKit for HTML processing.

Vendor	Apple (96 exploited CVEs in KEV)
Product	iOS, iPadOS, and macOS
Vulnerability	Apple iOS, iPadOS, and macOS WebKit Remote Code Execution Vulnerability
Weakness	CWE-1173
Published	2 Apr 2021
Added to KEV	3 Nov 2021
Reported by (CNA)	apple

What to do

Check whether you run it. Look for iOS, iPadOS, and macOS in your asset inventory, including appliances and cloud images. Stack check lists every exploited Apple CVE at once.
Apply the fix. Apply updates per vendor instructions.
If you can't patch today, take the affected service off the internet or restrict who can reach it, and check its logs for signs of compromise since 2 Apr 2021.
Get told next time. Email alerts when CISA adds a CVE for Apple.

Other exploited CVEs in iOS, iPadOS, and macOS

CVE-2025-43300: Apple iOS, iPadOS, and macOS Out-of-Bounds Write Vulnerability (21 Aug 2025)
CVE-2023-41064: Apple iOS, iPadOS, and macOS ImageIO Buffer Overflow Vulnerability (11 Sep 2023)
CVE-2023-28206: Apple iOS, iPadOS, and macOS IOSurfaceAccelerator Out-of-Bounds Write Vulnerability (10 Apr 2023)
CVE-2021-30900: Apple iOS, iPadOS, and macOS Out-of-Bounds Write Vulnerability (30 Mar 2023)
CVE-2022-32917: Apple iOS, iPadOS, and macOS Remote Code Execution Vulnerability (14 Sep 2022)
CVE-2020-9934: Apple iOS, iPadOS, and macOS Input Validation Vulnerability (8 Sep 2022)

References

nvd.nist.gov/vuln/detail/CVE-2021-1870

Questions

Is CVE-2021-1870 being exploited?

Yes. CISA added CVE-2021-1870 to the Known Exploited Vulnerabilities catalog on 3 Nov 2021, which means there is reliable evidence of exploitation in the wild.

Is CVE-2021-1870 used in ransomware attacks?

CISA does not list known ransomware use for it. That can change, and exploitation alone is reason to fix it first.

How do I fix CVE-2021-1870?

Apply updates per vendor instructions. Check Apple's advisory for the fixed versions, and if you can't patch quickly, restrict access to the affected iOS, iPadOS, and macOS and watch it for signs of compromise.

Sources: CISA KEV (exploitation, ransomware use, required action, due date), the CVE record (publication date, CVSS, CNA), NVD and FIRST EPSS (live score). More: all KEV additions in November 2021 · Apple scorecard · act-now radar.

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