CVE-2021-1879
CVE-2021-1879 is a security flaw in Apple iOS, iPadOS, and watchOS, the operating system on iPhones and iPads. Attackers can run code in the browser of someone using Apple iOS, iPadOS, and watchOS and act as them. The US Cybersecurity and Infrastructure Security Agency (CISA) added it to its catalog of flaws known to be used in attacks on 3 Nov 2021.[1]
Apple iOS, iPadOS, and watchOS is in things households have, such as phones, computers, browsers and everyday apps, so the fix matters at home as much as at work. Fixed in version 14.4, 12.5 and 7.3.
Description
CISA calls it a webKit cross-site scripting (XSS) in Apple iOS, iPadOS, and watchOS. In its words: “Apple iOS, iPadOS, and watchOS WebKit contain an unspecified vulnerability that allows for universal cross-site scripting (XSS) when processing maliciously crafted web content. 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.”[1]
The underlying weakness is cross-site scripting (CWE-79), in MITRE’s list of common software weaknesses.[2]
It scores 6.1 out of 10 on the Common Vulnerability Scoring System, which rates it medium, scored by NVD using CVSS 3.1.[2]
Affected versions
NVD’s record lists these fixed versions: in each line, everything before the version shown is affected.[2]
| Product | Fixed in |
|---|---|
| iOS and iPadOS | 14.4 |
| iOS | 12.5 |
| watchOS | 7.3 |
Every device with Apple iOS, iPadOS, and watchOS needs the update.
Exploitation
CISA added it to its catalog of known exploited vulnerabilities on 3 Nov 2021, 215 days after it was made public. CISA lists a flaw only when it has reliable evidence of it being exploited, and gave US federal agencies until 17 Nov 2021 to fix it.[1]
FIRST’s Exploit Prediction Scoring System, which estimates how likely a flaw is to be used in attacks in the next 30 days from what it sees across the internet, puts it at 7%. That’s in the top 6% of the flaws it scores.[4]
CISA assesses it as not automatable: each attack takes some work.
CISA doesn’t say who was attacked, or how.
Fix
Apple has published a fix or advice.[3] CISA’s required action: “Apply updates per vendor instructions.”[1]
- Update Apple iOS, iPadOS, and watchOS now.On iPhone and iPad: Settings, General, Software Update. On a Mac: System Settings, General, Software Update. Install it on every Apple device in the house. Then turn on automatic updates, so the next fix arrives on its own.
- Check you’re on 14.4 or later.Fixed in version 14.4, 12.5 and 7.3. Anything older is what attackers are going after.
- If there’s no update, stop using it.CISA’s advice when a flaw being used in attacks has no fix is to stop using the product until it does.
Timeline
| Date | Event |
|---|---|
| The flaw is made public in the National Vulnerability Database, with a severity score of 6.1.[2] | |
| CISA adds it to its catalog of flaws known to be used in attacks.[1] | |
| CISA’s deadline for US government agencies to fix it.[1] | |
| FIRST puts the odds of it being used in attacks in the next 30 days at 7%.[4] |
See also
Other Apple iOS, iPadOS, and watchOS flaws
- CVE-2023-41061: wallet code execution ·
- CVE-2020-9819: memory corruption ·
- CVE-2020-9818: out-of-bounds write ·
Other Apple flaws
- CVE-2026-86950, Apple devices: out-of-bounds write ·
- CVE-2026-65400, Apple macOS: improper authentication ·
- CVE-2025-43520, Apple devices: classic buffer overflow ·
- CVE-2025-43510, Apple devices: improper locking ·
- CVE-2025-31277, Apple devices: buffer overflow ·
Other cross-site scripting flaws
- CVE-2026-42897, Microsoft: exchange server cross-site scripting ·
- CVE-2025-48700, Synacor Zimbra Collaboration Suite (ZCS): cross-site scripting ·
- CVE-2025-66376, Synacor Zimbra Collaboration Suite (ZCS): cross-site scripting ·
- CVE-2025-68461, Roundcube Webmail: cross-site scripting ·
- CVE-2021-26829, OpenPLC ScadaBR: cross-site scripting ·
Added the same day
- CVE-2021-42258, BQE BillQuick Web Suite: SQL injection ·
- CVE-2021-42013, Apache HTTP Server: path traversal ·
- CVE-2021-41773, Apache HTTP Server: path traversal ·
- CVE-2021-40539, Zoho ManageEngine: aDSelfService plus authentication bypass ·
- CVE-2021-40444, Microsoft MSHTML: remote code execution ·
Every Apple flaw on CISA’s list · Everything added in November 2021
References
- ^ Cybersecurity and Infrastructure Security Agency. “Apple iOS, iPadOS, and watchOS WebKit Cross-Site Scripting (XSS) Vulnerability”. Known Exploited Vulnerabilities Catalog, added 3 Nov 2021.
- ^ National Institute of Standards and Technology. “CVE-2021-1879 Detail”. National Vulnerability Database, published 2 Apr 2021.
- ^ Apple. Advisories and fixes: support.apple.com, support.apple.com, support.apple.com.
- ^ FIRST. “Exploit Prediction Scoring System”. EPSS 0.071, percentile 94.2, 31 Oct 2026.
- CVE Program. “CVE-2021-1879”. The official CVE record.
This article is built from CISA’s catalog (version 2026.10.30), NVD’s record and FIRST’s scores, kept in HARD’s database and checked every morning. The plain English is HARD’s.