CVE-2020-3955Network attack vector

Stored cross-site scripting via unsanitized VM attributes

Published Apr 29, 2020 · Updated Aug 4, 2024

Stored XSS in VMware ESXi 6.5 and 6.7 allows attackers to execute script in a victim's browser through crafted VM attributes. The ESXi Host Client renders script-related HTML from guest-modifiable virtual-machine system properties without properly neutralizing it. The attacker must be able to change those properties from inside a guest OS, and execution requires a victim to view that VM in the Host Client.

CVSS severity8.3
High
EPSS probability1.34%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Stored XSS in VMware ESXi 6.5 and 6.7 allows attackers to execute script in a victim's browser through crafted VM attributes. The ESXi Host Client renders script-related HTML from guest-modifiable virtual-machine system properties without properly neutralizing it. The attacker must be able to change those properties from inside a guest OS, and execution requires a victim to view that VM in the Host Client.

The record

CVE
CVE-2020-3955
Published
Apr 29, 2020
Updated
Aug 4, 2024
Vendor
VMware
Product
VMware ESXi
Classifications
CWE-79, T1203
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 29, 2020CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=ESXi 6.5 without patch ESXi650-201912104-SG
  2. Affected versionversion=ESXi 6.7 without patch ESXi670-202004103-SG

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

VMware · VMware ESXiversion=ESXi 6.5 without patch ESXi650-201912104-SG; version=ESXi 6.7 without patch ESXi670-202004103-SG

Published CVSS scores

8.3VMwareCVSS:3.0/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:H/A:H
4.3NIST NVDAV:N/AC:M/Au:N/C:N/I:P/A:N
9.3NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
T1203Exploitation for Client Execution

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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