CVE-2021-30761
CVE-2021-30761 is a security flaw in Apple iOS, the operating system on iPhones and iPads. Attackers can run their own code on Apple iOS. 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 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 12.5 of iOS.
Description
CISA calls it a webKit memory corruption in Apple iOS. In its words: “Apple iOS WebKit contains a memory corruption vulnerability that leads to code execution 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 out-of-bounds write (CWE-787), in MITRE’s list of common software weaknesses.[2]
It scores 8.8 out of 10 on the Common Vulnerability Scoring System, which rates it high, scored by NVD using CVSS 3.1.[2]
Affected versions
NVD’s record lists one fixed version: everything before it is affected.[2]
| Product | Fixed in |
|---|---|
| iOS | 12.5 |
Every device with Apple iOS needs the update.
Exploitation
CISA added it to its catalog of known exploited vulnerabilities on 3 Nov 2021, 56 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 11%. That’s in the top 5% 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 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 12.5 or later.Fixed in version 12.5 of iOS. 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 8.8.[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 11%.[4] |
See also
Other Apple iOS flaws
- CVE-2022-42856: type confusion ·
- CVE-2016-4657: webkit memory corruption ·
- CVE-2016-4656: memory corruption ·
- CVE-2016-4655: information disclosure ·
- CVE-2019-7287: memory corruption ·
- CVE-2021-30762: webKit use-after-free ·
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 out-of-bounds write flaws
- CVE-2026-53266, Linux Kernel: out-of-bounds write ·
- CVE-2026-87491, Chrome and other Chromium browsers: out of bounds write ·
- CVE-2026-53362, Linux Kernel: unspecified ·
- CVE-2022-0995, Linux Kernel: out-of-bounds write ·
- CVE-2026-11645, Chrome and other Chromium browsers: out-of-bounds read and write ·
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 WebKit Memory Corruption Vulnerability”. Known Exploited Vulnerabilities Catalog, added 3 Nov 2021.
- ^ National Institute of Standards and Technology. “CVE-2021-30761 Detail”. National Vulnerability Database, published 8 Sep 2021.
- ^ Apple. Advisories and fixes: support.apple.com.
- ^ FIRST. “Exploit Prediction Scoring System”. EPSS 0.105, percentile 95.8, 31 Oct 2026.
- CVE Program. “CVE-2021-30761”. 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.