CVE-2021-0920
CVE-2021-0920 is a security flaw in Android Kernel, Google’s operating system for phones and tablets. Someone who already has a foothold can use Android Kernel to take full control of the machine. The US Cybersecurity and Infrastructure Security Agency (CISA) added it to its catalog of flaws known to be used in attacks on 23 May 2022.[1]
Android Kernel is in things households have, such as phones, computers, browsers and everyday apps, so the fix matters at home as much as at work. Android has published a fix or advice.
Description
CISA calls it a race condition in Android Kernel. In its words: “Android kernel contains a race condition, which allows for a use-after-free vulnerability. Exploitation can allow for privilege escalation.”[1]
The CVE record adds: “In unix_scm_to_skb of af_unix.c, there is a possible use after free bug due to a race condition. This could lead to local escalation of privilege with System execution privileges needed. User interaction is not needed for exploitation.Product: AndroidVersions: Android kernelAndroid ID: A-196926917References: Upstream kernel”[2]
The underlying weakness is race condition (CWE-362), use after free (CWE-416), in MITRE’s list of common software weaknesses.
It scores 6.4 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 doesn’t list version ranges for it; Android’s advisory has them[3]. CISA names the product as Android Kernel.
Every device with Android Kernel needs the update.
Exploitation
CISA added it to its catalog of known exploited vulnerabilities on 23 May 2022, 159 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 13 Jun 2022 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 under 1%. That’s in the top 42% 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
Android has published a fix or advice.[3] CISA’s required action: “Apply updates per vendor instructions.”[1]
- Update Android Kernel now.On Android: Settings, then System or Software update. Phones only get these fixes while their maker still supports them. Then turn on automatic updates, so the next fix arrives on its own.
- 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 6.4.[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 under 1%.[4] |
See also
Other Android Kernel flaws
- CVE-2024-36971: remote code execution ·
- CVE-2021-1048: use-after-free ·
Other Android flaws
- CVE-2025-48595, Android Framework: integer overflow ·
- CVE-2025-48633, Android Framework: information disclosure ·
- CVE-2025-48572, Android Framework: privilege escalation ·
- CVE-2025-48543, Android Runtime: use-after-free ·
- CVE-2024-43093, Android Framework: privilege escalation ·
Other race condition flaws
- CVE-2025-39964, Linux Kernel: race condition ·
- CVE-2025-62215, Microsoft Windows: race condition ·
- CVE-2023-36884, Microsoft Windows: search remote code execution ·
- CVE-2021-25395, Samsung Mobile Devices: race condition ·
- CVE-2014-0196, Linux Kernel: race condition ·
Added the same day
- CVE-2022-20821, Cisco IOS XR: open port ·
- CVE-2021-30883, Apple devices: memory corruption ·
- CVE-2021-1048, Android Kernel: use-after-free ·
- CVE-2020-1027, Microsoft Windows: kernel privilege escalation ·
- CVE-2020-0638, Microsoft Update Notification Manager: privilege escalation ·
Every Android flaw on CISA’s list · Everything added in May 2022
References
- ^ Cybersecurity and Infrastructure Security Agency. “Android Kernel Race Condition Vulnerability”. Known Exploited Vulnerabilities Catalog, added 23 May 2022.
- ^ National Institute of Standards and Technology. “CVE-2021-0920 Detail”. National Vulnerability Database, published 15 Dec 2021.
- ^ Android. Advisories and fixes: source.android.com.
- ^ FIRST. “Exploit Prediction Scoring System”. EPSS 0.009, percentile 58.7, 31 Oct 2026.
- CVE Program. “CVE-2021-0920”. 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.