How severe is CVE-2021-21991?

CVE-2021-21991 has a CVSS 3.x base score of 7.8, rated high severity. It is exploitable over local access with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2021-21991 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (22nd percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-21991?

CVE-2021-21991 primarily affects Vmware Cloud Foundation. In total, 56 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2021-21991?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

When was CVE-2021-21991 published?

CVE-2021-21991 was published on 2021-09-22 and last updated on 2026-06-17.

CVE-2021-21991

CVE-2021-21991 is a high-severity vulnerability in Vmware Cloud Foundation with a CVSS 3.x base score of 7.8. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low.

Key facts

Severity: High (CVSS 3.x base score 7.8)
CVSS v2: 4.6
EPSS exploit prediction: 0% (22nd percentile)
Actively exploited: Not listed in CISA KEV
Affected product: Vmware Cloud Foundation
Published: 2021-09-22
Last modified: 2026-06-17

Description

The vCenter Server contains a local privilege escalation vulnerability due to the way it handles session tokens. A malicious actor with non-administrative user access on vCenter Server host may exploit this issue to escalate privileges to Administrator on the vSphere Client (HTML5) or vCenter Server vSphere Web Client (FLEX/Flash).

Frequently asked questions

What is CVE-2021-21991?: The vCenter Server contains a local privilege escalation vulnerability due to the way it handles session tokens. A malicious actor with non-administrative user access on vCenter Server host may exploit this issue to escalate privileges to Administrator on the vSphere Client (HTML5) or vCenter Server vSphere Web Client (FLEX/Flash).
How severe is CVE-2021-21991?: CVE-2021-21991 has a CVSS 3.x base score of 7.8, rated high severity. It is exploitable over local access with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2021-21991 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (22nd percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-21991?: CVE-2021-21991 primarily affects Vmware Cloud Foundation. In total, 56 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-21991?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2021-21991 published?: CVE-2021-21991 was published on 2021-09-22 and last updated on 2026-06-17.

References

https://www.vmware.com/security/advisories/VMSA-2021-0020.html

Affected products (56)

cpe:2.3:a:vmware:cloud_foundation:*:*:*:*:*:*:*:*
cpe:2.3:a:vmware:vcenter_server:6.5:-:*:*:*:*:*:*
cpe:2.3:a:vmware:vcenter_server:6.5:a:*:*:*:*:*:*
cpe:2.3:a:vmware:vcenter_server:6.5:b:*:*:*:*:*:*
cpe:2.3:a:vmware:vcenter_server:6.5:c:*:*:*:*:*:*
cpe:2.3:a:vmware:vcenter_server:6.5:d:*:*:*:*:*:*
cpe:2.3:a:vmware:vcenter_server:6.5:e:*:*:*:*:*:*
cpe:2.3:a:vmware:vcenter_server:6.5:f:*:*:*:*:*:*
cpe:2.3:a:vmware:vcenter_server:6.5:update1:*:*:*:*:*:*
cpe:2.3:a:vmware:vcenter_server:6.5:update1b:*:*:*:*:*:*
cpe:2.3:a:vmware:vcenter_server:6.5:update1c:*:*:*:*:*:*
cpe:2.3:a:vmware:vcenter_server:6.5:update1d:*:*:*:*:*:*
cpe:2.3:a:vmware:vcenter_server:6.5:update1e:*:*:*:*:*:*
cpe:2.3:a:vmware:vcenter_server:6.5:update1g:*:*:*:*:*:*
cpe:2.3:a:vmware:vcenter_server:6.5:update2:*:*:*:*:*:*
cpe:2.3:a:vmware:vcenter_server:6.5:update2b:*:*:*:*:*:*
cpe:2.3:a:vmware:vcenter_server:6.5:update2c:*:*:*:*:*:*
cpe:2.3:a:vmware:vcenter_server:6.5:update2d:*:*:*:*:*:*
cpe:2.3:a:vmware:vcenter_server:6.5:update2g:*:*:*:*:*:*
cpe:2.3:a:vmware:vcenter_server:6.5:update3:*:*:*:*:*:*
cpe:2.3:a:vmware:vcenter_server:6.5:update3d:*:*:*:*:*:*
cpe:2.3:a:vmware:vcenter_server:6.5:update3f:*:*:*:*:*:*
cpe:2.3:a:vmware:vcenter_server:6.5:update3k:*:*:*:*:*:*
cpe:2.3:a:vmware:vcenter_server:6.5:update3n:*:*:*:*:*:*
cpe:2.3:a:vmware:vcenter_server:6.5:update3p:*:*:*:*:*:*
cpe:2.3:a:vmware:vcenter_server:6.7:*:*:*:*:*:*:*
cpe:2.3:a:vmware:vcenter_server:6.7:-:*:*:*:*:*:*
cpe:2.3:a:vmware:vcenter_server:6.7:a:*:*:*:*:*:*
cpe:2.3:a:vmware:vcenter_server:6.7:b:*:*:*:*:*:*
cpe:2.3:a:vmware:vcenter_server:6.7:d:*:*:*:*:*:*
cpe:2.3:a:vmware:vcenter_server:6.7:update1:*:*:*:*:*:*
cpe:2.3:a:vmware:vcenter_server:6.7:update1b:*:*:*:*:*:*
cpe:2.3:a:vmware:vcenter_server:6.7:update2:*:*:*:*:*:*
cpe:2.3:a:vmware:vcenter_server:6.7:update2a:*:*:*:*:*:*
cpe:2.3:a:vmware:vcenter_server:6.7:update2c:*:*:*:*:*:*
cpe:2.3:a:vmware:vcenter_server:6.7:update3:*:*:*:*:*:*
cpe:2.3:a:vmware:vcenter_server:6.7:update3a:*:*:*:*:*:*
cpe:2.3:a:vmware:vcenter_server:6.7:update3b:*:*:*:*:*:*
cpe:2.3:a:vmware:vcenter_server:6.7:update3f:*:*:*:*:*:*
cpe:2.3:a:vmware:vcenter_server:6.7:update3g:*:*:*:*:*:*

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