CVE-2021-21973
CVE-2021-21973 is a security flaw in VMware vCenter Server and Cloud Foundation, VMware’s software for running virtual machines in data centres. Attackers can make VMware vCenter Server and Cloud Foundation send requests into the network behind it. The US Cybersecurity and Infrastructure Security Agency (CISA) added it to its catalog of flaws known to be used in attacks on 7 Mar 2022.[1]
VMware vCenter Server and Cloud Foundation 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 a server side request forgery (SSRF) in VMware vCenter Server and Cloud Foundation. In its words: “VMware vCenter Server and Cloud Foundation Server contain a SSRF vulnerability due to improper validation of URLs in a vCenter Server plugin. This allows for information disclosure.”[1]
The CVE record adds: “The vSphere Client (HTML5) contains an SSRF (Server Side Request Forgery) vulnerability due to improper validation of URLs in a vCenter Server plugin. A malicious actor with network access to port 443 may exploit this issue by sending a POST request to vCenter Server plugin leading to information disclosure. This affects: VMware vCenter Server (7.x before 7.0 U1c, 6.7 before 6.7 U3l and 6.5 before 6.5 U3n) and VMware Cloud Foundation (4.x before 4.2 and 3.x before 3.10.1.2).”[2]
The underlying weakness is improper input validation (CWE-20), server-side request forgery (CWE-918), 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 and Cloud Foundation.
Most families won’t have VMware vCenter Server and Cloud Foundation; it’s for whoever looks after IT at work.
Exploitation
CISA added it to its catalog of known exploited vulnerabilities on 7 Mar 2022, 376 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 21 Mar 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 88%. That’s in the top 1% 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 and Cloud Foundation 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 21 Mar 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 88%.[4] |
See also
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-2024-38813, VMware vCenter Server: privilege escalation ·
- CVE-2024-38812, VMware vCenter Server: heap-based buffer overflow ·
Other improper input validation flaws
- CVE-2026-93952, Arista VeloCloud Orchestrator: improper input validation ·
- CVE-2019-1068, Microsoft SQL Server: remote code execution ·
- CVE-2026-12569, PTC Windchill and FlexPLM: improper input validation ·
- CVE-2026-34910, Ubiquiti UniFi OS: improper input validation ·
- CVE-2026-6973, Ivanti Endpoint Manager Mobile (EPMM): improper input validation ·
Added the same day
- CVE-2022-26486, Mozilla Firefox: use-after-free ·
- CVE-2022-26485, Mozilla Firefox: use-after-free ·
- CVE-2020-8218, Pulse Secure Pulse Connect Secure: code injection ·
- CVE-2019-11581, Atlassian Jira Server and Data Center: server-side template injection ·
- CVE-2017-6077, NETGEAR Wireless Router DGN2200: dGN2200 remote code execution ·
Every VMware flaw on CISA’s list · Everything added in March 2022
References
- ^ Cybersecurity and Infrastructure Security Agency. “VMware vCenter Server and Cloud Foundation Server Side Request Forgery (SSRF) Vulnerability”. Known Exploited Vulnerabilities Catalog, added 7 Mar 2022.
- ^ National Institute of Standards and Technology. “CVE-2021-21973 Detail”. National Vulnerability Database, published 24 Feb 2021.
- ^ VMware. Advisories and fixes: vmware.com.
- ^ FIRST. “Exploit Prediction Scoring System”. EPSS 0.880, percentile 99.8, 31 Oct 2026.
- CVE Program. “CVE-2021-21973”. 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.