CVE-2021-26035Network attack vector

Script execution via unescaped JForm Rules field

Published Jul 7, 2021 · Updated Feb 25, 2026

Cross-site scripting in the JForm Rules field in Joomla! CMS 3.0.0 through 3.9.27 allows remote attackers to run script via crafted form content. The JForm API renders attacker-controlled Rules-field content without adequate output escaping, so the browser interprets embedded markup as script. Exploitation requires a user to view the affected form output; script execution is confined to that user's browser context and can read or alter data available there.

CVSS severity6.1
Medium
EPSS probability0.72%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Cross-site scripting in the JForm Rules field in Joomla! CMS 3.0.0 through 3.9.27 allows remote attackers to run script via crafted form content. The JForm API renders attacker-controlled Rules-field content without adequate output escaping, so the browser interprets embedded markup as script. Exploitation requires a user to view the affected form output; script execution is confined to that user's browser context and can read or alter data available there.

The record

CVE
CVE-2021-26035
Published
Jul 7, 2021
Updated
Feb 25, 2026
Vendor
Joomla! Project
Product
Joomla! CMS
Classifications
CWE-79, T1203
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 7, 2021CVE publishedPublication date reported by the CVE source.
  2. Feb 25, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

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

  1. Affected versionversion=3.0.0-3.9.27

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Joomla! Project · Joomla! CMSversion=3.0.0-3.9.27

Published CVSS scores

4.3NIST NVDAV:N/AC:M/Au:N/C:N/I:P/A:N
6.1NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/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
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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