VulnerabilityPublished 16 Mar 2026

CVE-2026-4225: CMS Made Simple · Cross-site Scripting

Affects CMS Made SimpleSource CVE Database V5

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Public exploit available · CVSS 4.8 Medium.

Data as of 30 Oct 2026, 11:52 UTC

CVSS 4.0 base score

4.8Medium

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.2% chance of exploitation in 30 days – higher than 11% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:P/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:P

Base metrics

Attack Vector: Network
Attack Complexity: Low
Attack Requirements: None
Privileges Required: High
User Interaction: Passive
Vulnerable system confidentiality: None
Vulnerable system integrity: Low
Vulnerable system availability: None
Subsequent system confidentiality: None
Subsequent system integrity: None
Subsequent system availability: None

Threat metrics

Exploit Maturity: POC

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable system is bound to the network stack and the set of possible attackers extends beyond the other options listed below, up to and including the entire Internet. Such a vulnerability is often termed “remotely exploitable” and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: The attacker must take no measurable action to exploit the vulnerability. The attack requires no target-specific circumvention to exploit the vulnerability. An attacker can expect repeatable success against the vulnerable system.
Attack Requirements: None: The successful attack does not depend on the deployment and execution conditions of the vulnerable system. The attacker can expect to be able to reach the vulnerability and execute the exploit under all or most instances of the vulnerability.
Privileges Required: High: The attacker requires privileges that provide significant (e.g., administrative) control over the vulnerable system allowing full access to the vulnerable system’s settings and files.
User Interaction: Passive: Successful exploitation of this vulnerability requires limited interaction by the targeted user with the vulnerable system and the attacker’s payload. These interactions would be considered involuntary and do not require that the user actively subvert protections built into the vulnerable system.
Vulnerable system confidentiality: None: There is no loss of confidentiality within the Vulnerable System.
Vulnerable system integrity: Low: Modification of data is possible, but the attacker does not have control over the consequence of a modification, or the amount of modification is limited. The data modification does not have a direct, serious impact to the Vulnerable System.
Vulnerable system availability: None: There is no impact to availability within the Vulnerable System.
Subsequent system confidentiality: None: There is no loss of confidentiality within the Subsequent System or all confidentiality impact is constrained to the Vulnerable System.
Subsequent system integrity: None: There is no loss of integrity within the Subsequent System or all integrity impact is constrained to the Vulnerable System.
Subsequent system availability: None: There is no impact to availability within the Subsequent System or all availability impact is constrained to the Vulnerable System.
Exploit Maturity: POC: Based on threat intelligence sources each of the following must apply: · Proof-of-concept is publicly available · No knowledge of reported attempts to exploit this vulnerability · No knowledge of publicly available solutions used to simplify attempts to exploit the vulnerability

Definitions: FIRST CVSS v4.0 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 16 Mar 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: evidence found.
CVSS exploit maturity: proof of concept public
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), CVSS vector, the Metasploit, Exploit-DB and nuclei-templates index as of 30 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Affected software

Product	Affected	Fixed in
CMS Made Simple	Affected 2.2.0 – 2.2.21 22 affected builds	Fixed in–
Packagistcms/cms-made-simple`pkg:composer/cms/cms-made-simple`Other threats	Affected 2.2.0 – 2.2.21 22 affected builds	Fixed in–

CPE configurations (1)

cpe:2.3:a:cms_made_simple:cms_made_simple:*:*:*:*:*:*:*:*

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

To mitigate CVE-2026-4225, organizations should immediately upgrade CMS Made Simple to a version that addresses this vulnerability once available. In the absence of an official patch, administrators should implement strict input validation and output encoding on the 'Message' parameter in admin/listusers.php to neutralize malicious scripts. Employing a Web Application Firewall (WAF) with rules to detect and block XSS payloads targeting the User Management Module can provide temporary protection. Restrict administrative access to trusted IP addresses and enforce multi-factor authentication to reduce the risk of session hijacking. Regularly audit CMS logs for suspicious activities related to user management functions. Educate administrators about phishing risks and the importance of not interacting with unexpected messages or links within the CMS interface. Finally, consider isolating the CMS environment from critical internal networks to limit potential lateral movement if compromised.

Description

A security flaw has been discovered in CMS Made Simple up to 2.2.21. Impacted is an unknown function of the file admin/listusers.php of the component User Management Module. Performing a manipulation of the argument Message results in cross site scripting. The attack is possible to be carried out remotely. The exploit has been released to the public and may be used for attacks.

Impact

The primary impact of CVE-2026-4225 is the potential compromise of administrative sessions and unauthorized actions within CMS Made Simple installations. Successful exploitation can lead to session hijacking, enabling attackers to gain administrative control, modify site content, or access sensitive user data. This undermines the integrity of the CMS and could facilitate further attacks such as malware distribution or defacement. While the vulnerability does not directly expose confidential data or cause denial of service, the indirect consequences of administrative compromise can be severe, including reputational damage and loss of trust. Organizations relying on CMS Made Simple for website management, especially those with sensitive or high-traffic sites, face increased risk. The remote exploitability and public availability of exploit code heighten the urgency for remediation. Additionally, attackers could use this vulnerability as a foothold for lateral movement within an organization’s network if the CMS is integrated with internal systems.

Summary

CVE-2026-4225 is a medium-severity cross-site scripting vulnerability affecting CMS Made Simple versions 2.2.0 through 2.2.21. The vulnerability resides in the admin/listusers.php file, specifically within the User Management Module, where the 'Message' parameter is not properly sanitized before being rendered. This allows an attacker to inject arbitrary JavaScript code that executes in the context of an authenticated administrator's browser when they view the manipulated message. The attack vector is remote and does not require prior authentication, but successful exploitation depends on tricking an authorized user into interacting with the malicious payload (user interaction required). The CVSS 4.8 score reflects the attack vector as network accessible with low complexity, no privileges required, but requiring user interaction and resulting in limited integrity impact and no direct confidentiality or availability impact. The vulnerability could be leveraged to steal session cookies, perform actions on behalf of the administrator, or conduct phishing attacks within the CMS environment. Although no active exploits have been observed in the wild, the public availability of proof-of-concept code increases the risk of exploitation. The lack of official patches or updates at the time of disclosure necessitates immediate mitigation efforts by administrators. This vulnerability highlights the importance of input validation and output encoding in web applications, especially in administrative interfaces.

References

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