Vulnerability Database

383,304

Total vulnerabilities in the database

CVE-2021-21974 — vmware / cloud_foundation

Out-of-bounds Write

OpenSLP as used in ESXi (7.0 before ESXi70U1c-17325551, 6.7 before ESXi670-202102401-SG, 6.5 before ESXi650-202102101-SG) has a heap-overflow vulnerability. A malicious actor residing within the same network segment as ESXi who has access to port 427 may be able to trigger the heap-overflow issue in OpenSLP service resulting in remote code execution.

  • Published: Feb 24, 2021
  • Updated: Sep 13, 2026
  • CVE: CVE-2021-21974
  • Severity: High
  • Exploit:
  • CISA KEV:

CVSS v3:

  • Severity: High
  • Score: 8.8
  • AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CVSS v2:

  • Severity: Medium
  • Score: 5.8
  • AV:A/AC:L/Au:N/C:P/I:P/A:P

CWEs:

Software Affected versions
vmware / cloud_foundation >= 3.0, < 3.10.1.2
vmware / cloud_foundation >= 4.0, < 4.2
vmware / esxi = 6.5
vmware / esxi = 6.5-2
vmware / esxi = 6.5-650-201701001
vmware / esxi = 6.5-650-201703001
vmware / esxi = 6.5-650-201703002
vmware / esxi = 6.5-650-201704001
vmware / esxi = 6.5-650-201707101
vmware / esxi = 6.5-650-201707102
vmware / esxi = 6.5-650-201707103
vmware / esxi = 6.5-650-201707201
vmware / esxi = 6.5-650-201707202
vmware / esxi = 6.5-650-201707203
vmware / esxi = 6.5-650-201707204
vmware / esxi = 6.5-650-201707205
vmware / esxi = 6.5-650-201707206
vmware / esxi = 6.5-650-201707207
vmware / esxi = 6.5-650-201707208
vmware / esxi = 6.5-650-201707209
vmware / esxi = 6.5-650-201707210
vmware / esxi = 6.5-650-201707211
vmware / esxi = 6.5-650-201707212
vmware / esxi = 6.5-650-201707213
vmware / esxi = 6.5-650-201707214
vmware / esxi = 6.5-650-201707215
vmware / esxi = 6.5-650-201707216
vmware / esxi = 6.5-650-201707217
vmware / esxi = 6.5-650-201707218
vmware / esxi = 6.5-650-201707219
vmware / esxi = 6.5-650-201707220
vmware / esxi = 6.5-650-201707221
vmware / esxi = 6.5-650-201710001
vmware / esxi = 6.5-650-201712001
vmware / esxi = 6.5-650-201803001
vmware / esxi = 6.5-650-201806001
vmware / esxi = 6.5-650-201808001
vmware / esxi = 6.5-650-201810001
vmware / esxi = 6.5-650-201810002
vmware / esxi = 6.5-650-201811001
vmware / esxi = 6.5-650-201811002
vmware / esxi = 6.5-650-201811301
vmware / esxi = 6.5-650-201901001
vmware / esxi = 6.5-650-201903001
vmware / esxi = 6.5-650-201905001
vmware / esxi = 6.5-650-201908001
vmware / esxi = 6.5-650-201910001
vmware / esxi = 6.5-650-20191004001
vmware / esxi = 6.5-650-201911001
vmware / esxi = 6.5-650-201911401
vmware / esxi = 6.5-650-201911402
vmware / esxi = 6.5-650-201912001
vmware / esxi = 6.5-650-201912002
vmware / esxi = 6.5-650-201912101
vmware / esxi = 6.5-650-201912102
vmware / esxi = 6.5-650-201912103
vmware / esxi = 6.5-650-201912104
vmware / esxi = 6.5-650-201912301
vmware / esxi = 6.5-650-201912401
vmware / esxi = 6.5-650-201912402
vmware / esxi = 6.5-650-201912403
vmware / esxi = 6.5-650-201912404
vmware / esxi = 6.5-650-202005001
vmware / esxi = 6.5-650-202006001
vmware / esxi = 6.5-650-202007001
vmware / esxi = 6.5-650-202010001
vmware / esxi = 6.5-650-202011001
vmware / esxi = 6.5-650-202011002
vmware / esxi = 6.5-650-202102001
vmware / esxi = 6.7
vmware / esxi = 6.7-670-201806001
vmware / esxi = 6.7-670-201807001
vmware / esxi = 6.7-670-201808001
vmware / esxi = 6.7-670-201810001
vmware / esxi = 6.7-670-201810101
vmware / esxi = 6.7-670-201810102
vmware / esxi = 6.7-670-201810103
vmware / esxi = 6.7-670-201810201
vmware / esxi = 6.7-670-201810202
vmware / esxi = 6.7-670-201810203
vmware / esxi = 6.7-670-201810204
vmware / esxi = 6.7-670-201810205
vmware / esxi = 6.7-670-201810206
vmware / esxi = 6.7-670-201810207
vmware / esxi = 6.7-670-201810208
vmware / esxi = 6.7-670-201810209
vmware / esxi = 6.7-670-201810210
vmware / esxi = 6.7-670-201810211
vmware / esxi = 6.7-670-201810212
vmware / esxi = 6.7-670-201810213
vmware / esxi = 6.7-670-201810214
vmware / esxi = 6.7-670-201810215
vmware / esxi = 6.7-670-201810216
vmware / esxi = 6.7-670-201810217
vmware / esxi = 6.7-670-201810218
vmware / esxi = 6.7-670-201810219
vmware / esxi = 6.7-670-201810220
vmware / esxi = 6.7-670-201810221
vmware / esxi = 6.7-670-201810222
vmware / esxi = 6.7-670-201810223
vmware / esxi = 6.7-670-201810224
vmware / esxi = 6.7-670-201810225
vmware / esxi = 6.7-670-201810226
vmware / esxi = 6.7-670-201810227
vmware / esxi = 6.7-670-201810228
vmware / esxi = 6.7-670-201810229
vmware / esxi = 6.7-670-201810230
vmware / esxi = 6.7-670-201810231
vmware / esxi = 6.7-670-201810232
vmware / esxi = 6.7-670-201810233
vmware / esxi = 6.7-670-201810234
vmware / esxi = 6.7-670-201811001
vmware / esxi = 6.7-670-201901001
vmware / esxi = 6.7-670-201901401
vmware / esxi = 6.7-670-201901402
vmware / esxi = 6.7-670-201901403
vmware / esxi = 6.7-670-201903001
vmware / esxi = 6.7-670-201904001
vmware / esxi = 6.7-670-201904201
vmware / esxi = 6.7-670-201904201-ug
vmware / esxi = 6.7-670-201904202
vmware / esxi = 6.7-670-201904202-ug
vmware / esxi = 6.7-670-201904203
vmware / esxi = 6.7-670-201904203-ug
vmware / esxi = 6.7-670-201904204
vmware / esxi = 6.7-670-201904204-ug
vmware / esxi = 6.7-670-201904205
vmware / esxi = 6.7-670-201904205-ug
vmware / esxi = 6.7-670-201904206
vmware / esxi = 6.7-670-201904206-ug
vmware / esxi = 6.7-670-201904207
vmware / esxi = 6.7-670-201904207-ug
vmware / esxi = 6.7-670-201904208
vmware / esxi = 6.7-670-201904208-ug
vmware / esxi = 6.7-670-201904209
vmware / esxi = 6.7-670-201904209-ug
vmware / esxi = 6.7-670-201904210
vmware / esxi = 6.7-670-201904210-ug
vmware / esxi = 6.7-670-201904211
vmware / esxi = 6.7-670-201904211-ug
vmware / esxi = 6.7-670-201904212
vmware / esxi = 6.7-670-201904212-ug
vmware / esxi = 6.7-670-201904213
vmware / esxi = 6.7-670-201904213-ug
vmware / esxi = 6.7-670-201904214
vmware / esxi = 6.7-670-201904214-ug
vmware / esxi = 6.7-670-201904215
vmware / esxi = 6.7-670-201904215-ug
vmware / esxi = 6.7-670-201904216
vmware / esxi = 6.7-670-201904216-ug
vmware / esxi = 6.7-670-201904217
vmware / esxi = 6.7-670-201904217-ug
vmware / esxi = 6.7-670-201904218
vmware / esxi = 6.7-670-201904218-ug
vmware / esxi = 6.7-670-201904219
vmware / esxi = 6.7-670-201904219-ug
vmware / esxi = 6.7-670-201904220
vmware / esxi = 6.7-670-201904220-ug
vmware / esxi = 6.7-670-201904221
vmware / esxi = 6.7-670-201904221-ug
vmware / esxi = 6.7-670-201904222
vmware / esxi = 6.7-670-201904222-ug
vmware / esxi = 6.7-670-201904223
vmware / esxi = 6.7-670-201904223-ug
vmware / esxi = 6.7-670-201904224
vmware / esxi = 6.7-670-201904224-ug
vmware / esxi = 6.7-670-201904225
vmware / esxi = 6.7-670-201904225-ug
vmware / esxi = 6.7-670-201904226
vmware / esxi = 6.7-670-201904226-ug
vmware / esxi = 6.7-670-201904227
vmware / esxi = 6.7-670-201904227-ug
vmware / esxi = 6.7-670-201904228
vmware / esxi = 6.7-670-201904228-ug
vmware / esxi = 6.7-670-201904229
vmware / esxi = 6.7-670-201904229-ug
vmware / esxi = 6.7-670-201905001
vmware / esxi = 6.7-670-201906002
vmware / esxi = 6.7-670-201908101
vmware / esxi = 6.7-670-201908102
vmware / esxi = 6.7-670-201908103
vmware / esxi = 6.7-670-201908104
vmware / esxi = 6.7-670-201908201
vmware / esxi = 6.7-670-201908202
vmware / esxi = 6.7-670-201908203
vmware / esxi = 6.7-670-201908204
vmware / esxi = 6.7-670-201908205
vmware / esxi = 6.7-670-201908206
vmware / esxi = 6.7-670-201908207
vmware / esxi = 6.7-670-201908208
vmware / esxi = 6.7-670-201908209
vmware / esxi = 6.7-670-201908210
vmware / esxi = 6.7-670-201908211
vmware / esxi = 6.7-670-201908212
vmware / esxi = 6.7-670-201908213
vmware / esxi = 6.7-670-201908214
vmware / esxi = 6.7-670-201908215
vmware / esxi = 6.7-670-201908216
vmware / esxi = 6.7-670-201908217
vmware / esxi = 6.7-670-201908218
vmware / esxi = 6.7-670-201908219
vmware / esxi = 6.7-670-201908220
vmware / esxi = 6.7-670-201908221
vmware / esxi = 6.7-670-201912001
vmware / esxi = 6.7-670-201912101
vmware / esxi = 6.7-670-201912102
vmware / esxi = 6.7-670-201912401
vmware / esxi = 6.7-670-201912402
vmware / esxi = 6.7-670-201912403
vmware / esxi = 6.7-670-201912404
vmware / esxi = 6.7-670-201912405
vmware / esxi = 6.7-670-202004001
vmware / esxi = 6.7-670-202004002
vmware / esxi = 6.7-670-202004301
vmware / esxi = 6.7-670-202004401
vmware / esxi = 6.7-670-202004402
vmware / esxi = 6.7-670-202004403
vmware / esxi = 6.7-670-202004404
vmware / esxi = 6.7-670-202004405
vmware / esxi = 6.7-670-202004406
vmware / esxi = 6.7-670-202004407
vmware / esxi = 6.7-670-202004408
vmware / esxi = 6.7-670-202006001
vmware / esxi = 6.7-670-202008001
vmware / esxi = 6.7-670-202010001
vmware / esxi = 6.7-670-202011001
vmware / esxi = 6.7-670-202011002
vmware / esxi = 6.7-670-202102001
vmware / esxi = 7.0.0
vmware / esxi = 7.0.0-b
vmware / esxi = 7.0.0-update_1
vmware / esxi = 7.0.0-update_1a
vmware / esxi = 7.0.0-update_1b

Frequently Asked Questions

A security vulnerability is a weakness in software, hardware, or configuration that can be exploited to compromise confidentiality, integrity, or availability. Many vulnerabilities are tracked as CVEs (Common Vulnerabilities and Exposures), which provide a standardized identifier so teams can coordinate patching, mitigation, and risk assessment across tools and vendors.

CVSS (Common Vulnerability Scoring System) estimates technical severity, but it doesn't automatically equal business risk. Prioritize using context like internet exposure, affected asset criticality, known exploitation (proof-of-concept or in-the-wild), and whether compensating controls exist. A "Medium" CVSS on an exposed, production system can be more urgent than a "Critical" on an isolated, non-production host.

A vulnerability is the underlying weakness. An exploit is the method or code used to take advantage of it. A zero-day is a vulnerability that is unknown to the vendor or has no publicly available fix when attackers begin using it. In practice, risk increases sharply when exploitation becomes reliable or widespread.

Recurring findings usually come from incomplete Asset Discovery, inconsistent patch management, inherited images, and configuration drift. In modern environments, you also need to watch the software supply chain: dependencies, containers, build pipelines, and third-party services can reintroduce the same weakness even after you patch a single host. Unknown or unmanaged assets (often called Shadow IT) are a common reason the same issues resurface.

Use a simple, repeatable triage model: focus first on externally exposed assets, high-value systems (identity, VPN, email, production), vulnerabilities with known exploits, and issues that enable remote code execution or privilege escalation. Then enforce patch SLAs and track progress using consistent metrics so remediation is steady, not reactive.

SynScan combines attack surface monitoring and continuous security auditing to keep your inventory current, flag high-impact vulnerabilities early, and help you turn raw findings into a practical remediation plan.