CVE-2021-22017
CVE-2021-22017 is a security flaw in VMware vCenter Server, VMware’s software for running virtual machines in data centres. Attackers can reach parts of VMware vCenter Server that should be locked to them. The US Cybersecurity and Infrastructure Security Agency (CISA) added it to its catalog of flaws known to be used in attacks on 10 Jan 2022.[1]
VMware vCenter Server 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. VMware has published a fix or advice.
Description
CISA calls it an improper access control in VMware vCenter Server. In its words: “Rhttproxy as used in vCenter Server contains a vulnerability due to improper implementation of URI normalization.”[1]
The CVE record adds: “Rhttproxy as used in vCenter Server contains a vulnerability due to improper implementation of URI normalization. A malicious actor with network access to port 443 on vCenter Server may exploit this issue to bypass proxy leading to internal endpoints being accessed.”[2]
The underlying weakness is CWE-23, in MITRE’s list of common software weaknesses.
It scores 5.3 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; VMware’s advisory has them[3]. CISA names the product as VMware vCenter Server.
Most families won’t have VMware vCenter Server; it’s for whoever looks after IT at work.
Exploitation
CISA added it to its catalog of known exploited vulnerabilities on 10 Jan 2022, 109 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 24 Jan 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 49%. That’s in the top 2% of the flaws it scores.[4]
CISA assesses it as automatable: attackers can run it against many targets at once.
CISA doesn’t say who was attacked, or how.
Fix
VMware has published a fix or advice.[3] CISA’s required action: “Apply updates per vendor instructions.”[1]
- Check whether you use it.VMware vCenter Server 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, or not in use. CISA gave US government agencies until 24 Jan 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 5.3.[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 49%.[4] |
See also
Other VMware vCenter Server flaws
- CVE-2024-38813: privilege escalation ·
- CVE-2024-38812: heap-based buffer overflow ·
- CVE-2022-22948: incorrect default file permissions ·
- CVE-2023-34048: out-of-bounds write ·
- CVE-2021-22005: file upload ·
- CVE-2021-21985: improper input validation ·
Other VMware flaws
- CVE-2025-22226, VMware ESXi, Workstation, and Fusion: information disclosure ·
- CVE-2025-22225, VMware ESXi: arbitrary write ·
- CVE-2025-22224, VMware ESXi and Workstation: TOCTOU race condition ·
- CVE-2024-37085, VMware ESXi: authentication bypass ·
- CVE-2023-20867, VMware Tools: authentication bypass ·
Similar flaws
- CVE-2026-76519, Cisco Secure Email Gateway: relative path traversal ·
- CVE-2026-34926, Trend Micro Apex One: (on-premise) directory traversal ·
- CVE-2024-27199, JetBrains TeamCity: relative path traversal ·
- CVE-2025-64446, Fortinet FortiWeb: path traversal ·
- CVE-2022-37042, Synacor Zimbra Collaboration Suite (ZCS): authentication bypass ·
Added the same day
- CVE-2021-36260, Hikvision Security cameras web server: improper input validation ·
- CVE-2021-27860, FatPipe WARP, IPVPN, and MPVPN software: WARP, IPVPN, and MPVPN configuration upload exploit ·
- CVE-2020-6572, Google Chrome Media: use-after-free ·
- CVE-2019-9670, Synacor Zimbra Collaboration Suite (ZCS): improper restriction of XML external entity reference ·
- CVE-2019-7609, Elastic Kibana: arbitrary code execution ·
Every VMware flaw on CISA’s list · Everything added in January 2022
References
- ^ Cybersecurity and Infrastructure Security Agency. “VMware vCenter Server Improper Access Control”. Known Exploited Vulnerabilities Catalog, added 10 Jan 2022.
- ^ National Institute of Standards and Technology. “CVE-2021-22017 Detail”. National Vulnerability Database, published 23 Sep 2021.
- ^ VMware. Advisories and fixes: vmware.com.
- ^ FIRST. “Exploit Prediction Scoring System”. EPSS 0.492, percentile 98.9, 31 Oct 2026.
- CVE Program. “CVE-2021-22017”. 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.