VMware ESXi and Horizon DaaS OpenSLP Heap-Based Buffer Overflow Vulnerability

OpenSLP as used in ESXi and the Horizon DaaS appliances has a heap overwrite issue. VMware has evaluated the severity of this issue to be in the Critical severity range with a maximum CVSSv3 base score of 9.8.

CheckOps priority index

9.9/10 Patch within 24 h

Severity9.8

Probability9.8

Exploitation5/5

Severity = CVSS. Probability = EPSS (FIRST). Exploitation = public signals: KEV, EUVD, ransomware, EPSS above 10 %, no account required.

EPSS · today 98.1% higher than 99.9% of CVEs

CVSS 3.1 9.8 AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:

Exploited for 1,826 days 03 Nov 2021

CISA due date 03 May 2022 for US federal agencies

Exploitation probability EPSS · FIRST

EPSS probability (%)Percentile among all CVEs

Exploitation signals 5 / 5

KEV catalog (CISA)03 Nov 2021
Exploited in EUVD (ENISA)03 Nov 2021
Used by ransomwareyes
EPSS above 10 %98.1%
No account, over the networkyes

What to do

Fix

Apply the vendor’s fix as soon as it is available.

CISA guidance: Apply updates per vendor instructions.

Meanwhile

Take the service off the internet or restrict access to it, watch the logs and look for signs of compromise.

Manufacturers (CRA)

Exploited vulnerability in your product: early warning to ENISA within 24 h, then notification within 72 h (Article 14 of the Cyber Resilience Act). The CRA explained

Affected products

ESXi and Horizon DaaSVMware ESXi and Horizon DaaS

Affected versions

ESXi 6.7 prior to patch release ESXi670-201912001, ESXi 6.5 prior to patch release ESXi650-201912001, ESXi 6.0 prior to patch release ESXi600-201912001 and Horizon DaaS 8.x prior to BZ-2467224-Disable_SLPD_service_permanently_801_Hotfix.

Weaknesses (CWE)

CWE-787

Open source packages OSV

Affected libraries according to OSV, with fixed versions.

Timeline

06 Dec 2019
Published
03 Nov 2021
Exploitation reported (ENISA)
03 Nov 2021
Added to the KEV catalog
03 May 2022
CISA remediation due date
19 Oct 2026
EPSS peak: 98.1%

References

Other exploited vulnerabilities from the same vendor

CVE-2025-22226VMware ESXi, Workstation, and Fusion Information Disclosure Vulnerability
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CVE-2025-22225VMware ESXi Arbitrary Write Vulnerability
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CVE-2025-22224VMware ESXi and Workstation TOCTOU Race Condition Vulnerability
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CVE-2024-38813VMware vCenter Server Privilege Escalation Vulnerability
5.3 · Background exploitation
CVE-2024-38812VMware vCenter Server Heap-Based Buffer Overflow Vulnerability
8.0 · Background exploitation
CVE-2024-37085VMware ESXi Authentication Bypass Vulnerability
5.9 · Background exploitation