How severe is CVE-2021-1879?

CVE-2021-1879 has a CVSS score of 6.1/10, rated MEDIUM. Review your exposure and patch according to your risk tolerance.

Which packages are affected by CVE-2021-1879?

Affected package information for CVE-2021-1879 is not yet fully mapped. Check the official advisory links for details.

How do I fix CVE-2021-1879?

No fixed version has been published for CVE-2021-1879 yet. Monitor the advisory for updates, apply mitigations recommended by the vendor, and use O3 Security to track when a fix becomes available in your stack.

Is CVE-2021-1879 actively exploited in the wild?

Yes. There are 3 known exploit references for CVE-2021-1879, including 3 in-the-wild exploitations observed on GitHub and other sources. Treat this as actively exploitable and prioritize patching immediately. All exploit code should only be run in an isolated sandbox environment for research or authorized testing — never against production systems without explicit written authorization.

What is the EPSS score for CVE-2021-1879?

CVE-2021-1879 has an EPSS (Exploit Prediction Scoring System) score of 0.8%, placing it in the 75th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

Is CVE-2021-1879 in the CISA Known Exploited Vulnerabilities catalog?

Yes. CVE-2021-1879 (Apple iOS, iPadOS, and watchOS WebKit Cross-Site Scripting (XSS) Vulnerability) was added to CISA's Known Exploited Vulnerabilities (KEV) catalog on 2021-11-03. CISA required all US federal civilian agencies to remediate this vulnerability by 2021-11-17. The required action was: Apply updates per vendor instructions. Being listed in the KEV catalog is the strongest possible confirmation of active exploitation — treat this as a critical priority.

What type of vulnerability is CVE-2021-1879?

CVE-2021-1879 is classified as Cross-site Scripting (XSS) (CWE-79). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation. This is a high-impact weakness class that often enables remote code execution or data exposure.

Which products and versions are affected by CVE-2021-1879?

CVE-2021-1879 affects apple ipados; apple iphone os; apple watchos. Check the affected-products list on this page against your deployed version to confirm exposure.

When was CVE-2021-1879 published, and has it been updated?

CVE-2021-1879 was published on April 2, 2021 and was last updated on October 23, 2025. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

CISA KEV·Added 2021-11-03 — agencies required to remediate by 2021-11-17

CVE-2021-1879

MEDIUM

This issue was addressed by improved management of object lifetimes. This issue is fixed in iOS 12.5.2, iOS 14.4.2 and iPadOS 14.4.2, watchOS 7.3.3. Processing maliciously crafted web…

Published

Apr 2, 2021

Updated

Oct 23, 2025

Affected

0 pkgs

Patched

None yet

Exploits

3 known

EPSS Exploitation Probability

via FIRST.org ↗

0.8%probability of exploitation in next 30 days

Lower Risk75th percentile0.00%

EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.

Description

This issue was addressed by improved management of object lifetimes. This issue is fixed in iOS 12.5.2, iOS 14.4.2 and iPadOS 14.4.2, watchOS 7.3.3. Processing maliciously crafted web content may lead to universal cross site scripting. Apple is aware of a report that this issue may have been actively exploited..

Affected Products

3 products · 4 configurations

ipadosapple

< 14.4.2

range

iphone osapple

≥ 13.0 && < 14.4.2

range

watchosapple

< 7.3.3

range

Exploits & PoCs

Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.

This issue was addressed by improved management of object lifetimes. Thi…

support.apple.comGoogle-sheetMar 2021

This issue was addressed by improved management of object lifetimes. Thi…

nvd.nist.govNVDApr 2021

This issue was addressed by improved management of object lifetimes. Thi…

cisa.govCISANov 2021

Frequently Asked Questions

O3 Security · Impact-Aware SCA

Is CVE-2021-1879 in your stack?

O3 detects CVE-2021-1879 across dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.

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