CVE-2020-20391Public exploitNetwork attack vector

Stored XSS via unescaped snippet titles

Published Jun 23, 2021 · Updated Aug 4, 2024

Stored XSS in admin/snippets.php in GetSimpleCMS 3.4.0a allows remote authenticated users to run script in another user's browser. The Add Snippet flow stores an attacker-supplied snippet title and later renders it on admin/snippets.php without neutralizing HTML event handlers. An authenticated user must save the title and a second user must revisit the snippets page, causing the payload to execute in that user's browser context.

CVSS severity5.4
Medium
EPSS probability0.58%
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 admin/snippets.php in GetSimpleCMS 3.4.0a allows remote authenticated users to run script in another user's browser. The Add Snippet flow stores an attacker-supplied snippet title and later renders it on admin/snippets.php without neutralizing HTML event handlers. An authenticated user must save the title and a second user must revisit the snippets page, causing the payload to execute in that user's browser context.

The record

CVE
CVE-2020-20391
Published
Jun 23, 2021
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-79, T1203
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Jun 23, 2021CVE 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

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

3.5INCIBE-CERTAV:N/AC:M/Au:S/C:N/I:P/A:N
5.4INCIBE-CERTCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/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
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

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

Public exploit references

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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