CVE-2021-22600
CVE-2021-22600 is a security flaw in Linux Kernel, the core of Linux, which runs most servers, Android phones and many home routers. Someone who already has a foothold can use Linux 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 11 Apr 2022.[1]
Linux Kernel is business software or equipment. Most families won’t have it, but attackers break into it to get inside companies, and from there to what those companies hold about their customers, patients and staff. Fixed in version 5.4.168, 5.10.88, 5.15.11 and 5.16-rc6 of Kernel.
Description
CISA calls it a privilege escalation in Linux Kernel. In its words: “Linux Kernel contains a flaw in the packet socket (AF_PACKET) implementation which could lead to incorrectly freeing memory. A local user could exploit this for denial-of-service (DoS) or possibly for privilege escalation.”[1]
The CVE record adds: “A double free bug in packet_set_ring() in net/packet/af_packet.c can be exploited by a local user through crafted syscalls to escalate privileges or deny service. We recommend upgrading kernel past the effected versions or rebuilding past ec6af094ea28f0f2dda1a6a33b14cd57e36a9755”[2]
The underlying weakness is CWE-415, in MITRE’s list of common software weaknesses.
It scores 7.0 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 these fixed versions: in each line, everything before the version shown is affected.[2]
| Product | Fixed in |
|---|---|
| Kernel | 5.4.168 |
| Kernel | 5.10.88 |
| Kernel | 5.15.11 |
| Kernel | 5.16-rc6 |
Most families won’t have Linux Kernel; it’s for whoever looks after IT at work.
Exploitation
CISA added it to its catalog of known exploited vulnerabilities on 11 Apr 2022, 75 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 2 May 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 7%. That’s in the top 7% 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
Linux has published a fix or advice.[3] CISA’s required action: “Apply updates per vendor instructions.”[1]
- Check whether you use it.Linux Kernel is business software or equipment, so most families won’t have it. If you run a business, or work from home on company equipment, ask whoever looks after your IT.
- Send this page to your IT person.Ask them to confirm it’s fixed (fixed in version 5.4.168, 5.10.88, 5.15.11 and 5.16-rc6 of Kernel), or not in use. CISA gave US government agencies until 2 May 2022 to fix it.
- If it can’t be fixed, take it offline.CISA’s advice when there’s no fix is to stop using the product, or take it off the internet, until there is one.
You can’t fix someone else’s server, but you can watch for what follows a break-in like this: a breach notice, a password reset you didn’t ask for, or a scam message that knows things it shouldn’t. HARD watches for those for you and your family.
Timeline
| Date | Event |
|---|---|
| The flaw is made public in the National Vulnerability Database, with a severity score of 7.0.[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 Linux Kernel flaws
- CVE-2026-46300: missing initialization of a variable ·
- CVE-2026-53266: out-of-bounds write ·
- CVE-2025-39964: race condition ·
- CVE-2025-39682: improper check for unusual or exceptional conditions ·
- CVE-2026-53362: unspecified ·
- CVE-2022-0995: out-of-bounds write ·
Similar flaws
- CVE-2026-33824, Microsoft Internet Key Exchange (IKE) Service Extensions: double free ·
- CVE-2018-4990, Adobe Acrobat and Reader: double free ·
- CVE-2020-9859, Apple devices: code execution ·
Added the same day
- CVE-2022-23176, WatchGuard Firebox and XTM: privilege escalation ·
- CVE-2021-42287, Microsoft Active Directory: domain services privilege escalation ·
- CVE-2021-42278, Microsoft Active Directory: domain services privilege escalation ·
- CVE-2021-39793, Google Pixel: out-of-bounds write ·
- CVE-2021-27852, Checkbox Survey: survey deserialization of untrusted data ·
Every Linux flaw on CISA’s list · Everything added in April 2022
References
- ^ Cybersecurity and Infrastructure Security Agency. “Linux Kernel Privilege Escalation Vulnerability”. Known Exploited Vulnerabilities Catalog, added 11 Apr 2022.
- ^ National Institute of Standards and Technology. “CVE-2021-22600 Detail”. National Vulnerability Database, published 26 Jan 2022.
- ^ Linux. Advisories and fixes: git.kernel.org.
- ^ FIRST. “Exploit Prediction Scoring System”. EPSS 0.066, percentile 93.8, 31 Oct 2026.
- CVE Program. “CVE-2021-22600”. 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.