CVE-2026-81926: Concrete CMS: stored XSS via page path in dialog

MEDIUM

Published September 15, 2026

CISO Take

Concrete CMS 9.4.0 through 9.5.2 fails to escape colliding page paths in the location panel's duplicate-path confirmation dialog, letting a crafted path run script in an editor's authenticated browser session. This is a generic web CMS flaw and not an AI/ML-specific one. Nothing in the data shows an AI package or AI pipeline is affected, so the AI relevance is minimal. Urgency is low: EPSS is 0.00256 (84th percentile), it is not in CISA KEV, there is no public exploit or Nuclei template, and the CISA SSVC decision is TRACK. The vendor's own CVSS v4.0 score is 2.0 because exploitation needs high privileges and user interaction. Upgrade to the fixed release described in the Concrete CMS 9.5.3 release notes, and review whether any AI content workflows or admin consoles are integrated with the CMS.

Sources:NVDEPSSATLASdocumentation.concretecms.org

What is the risk?

Low overall risk. The vendor rates it CVSS v4.0 2.0 (high privileges and user interaction required), while the NVD-style CVSS v3.1 of 6.1 overstates it. Exploitation requires an editor-level account that can create colliding page paths and a victim editor who triggers the dialog. There is no known exploitation, no public exploit, and SSVC is TRACK. AI-specific exposure is negligible unless the CMS fronts AI/ML dashboards or content pipelines.

How does the attack unfold?

Initial Access

Attacker with editor-level privileges creates pages with crafted colliding paths containing script payloads.

AML.T0049

User Interaction

Another editor opens the location panel and triggers the duplicate-path confirmation dialog.

Exploitation

The check endpoint returns the unescaped path and client-side JavaScript inserts it as raw HTML, executing the script.

Impact

Script acts within the victim editor's authenticated session, enabling content tampering or unauthorized actions.

Initial Access

Attacker with editor-level privileges creates pages with crafted colliding paths containing script payloads.

AML.T0049

User Interaction

Another editor opens the location panel and triggers the duplicate-path confirmation dialog.

Exploitation

The check endpoint returns the unescaped path and client-side JavaScript inserts it as raw HTML, executing the script.

Impact

Script acts within the victim editor's authenticated session, enabling content tampering or unauthorized actions.

How severe is it?

CVSS 3.1

6.1 / 10

EPSS

0.3%

chance of exploitation in 30 days

Higher than 17% of all CVEs

Source: EPSS v3 — FIRST.org

Exploitation Status

No known exploitation

Sophistication

Moderate

What is the attack surface?

AVNetwork

ACLow

PRNone

UIRequired

SChanged

CLow

ILow

ANone

What should I do?

1 step

1) Upgrade Concrete CMS to the version after 9.5.2, as described in the 9.5.3 release notes. 2) Restrict page-creation and editor permissions to trusted users and audit recent page paths for HTML or script characters. 3) Apply a strict Content-Security-Policy on the admin interface to limit inline script execution. 4) Review editor session logs for unusual activity. 5) Track the issue through normal patch cycles, since no emergency action is warranted.

What does CISA's SSVC say?

DecisionTrack

Exploitationnone

AutomatableNo

Technical Impactpartial

Source: CISA Vulnrichment (SSVC v2.0). Decision based on the CISA Coordinator decision tree.

How is it classified?

Code ExecutionSocial EngineeringFrameworkAML.T0049- Exploit Public-Facing Application

Which compliance frameworks are affected?

This CVE is relevant to:

NIST AI RMF

MANAGE 2.3-Responses to previously unknown risks and mechanisms to supersede or deactivate AI systems

Frequently Asked Questions

What is CVE-2026-81926?

Is CVE-2026-81926 actively exploited?

No confirmed active exploitation of CVE-2026-81926 has been reported, but organizations should still patch proactively.

How to fix CVE-2026-81926?

1) Upgrade Concrete CMS to the version after 9.5.2, as described in the 9.5.3 release notes. 2) Restrict page-creation and editor permissions to trusted users and audit recent page paths for HTML or script characters. 3) Apply a strict Content-Security-Policy on the admin interface to limit inline script execution. 4) Review editor session logs for unusual activity. 5) Track the issue through normal patch cycles, since no emergency action is warranted.

What systems are affected by CVE-2026-81926?

This vulnerability affects the following AI/ML architecture patterns: Web CMS admin interfaces, Content management for AI documentation sites.

What is the CVSS score for CVE-2026-81926?

CVE-2026-81926 has a CVSS v3.1 base score of 6.1 (MEDIUM). The EPSS exploitation probability is 0.26%.

What is the AI security impact?

Affected AI Architectures

Web CMS admin interfacesContent management for AI documentation sites

MITRE ATLAS Techniques

AML.T0049Exploit Public-Facing Application

Compliance Controls Affected

NIST AI RMF: MANAGE 2.3

What are the technical details?

Original Advisory

Concrete CMS 9.4.0 through 9.5.2 did not escape colliding page paths before rendering them in the location panel's duplicate-path confirmation dialog. The panel's check endpoint returned the submitted path unmodified in its JSON response, and client-side JavaScript inserted each value into the dialog as raw HTML, so a crafted page path executed script in the editor's authenticated browser session. The Concrete CMS security team gave this vulnerability a CVSS v4.0 score of 2.0 with vector CVSS:4.0/AV:N/AC:L/AT:P/PR:H/UI:P/VC:L/VI:L/VA:L/SC:N/SI:N/SA:N. Thanks Yonatan Drori from Tenzai for reporting.

Exploitation Scenario

A malicious or compromised editor creates two pages whose paths contain an HTML or script payload so they collide. When another editor opens the location panel and triggers the duplicate-path confirmation, the check endpoint returns the unescaped path and client-side JavaScript inserts it as raw HTML. The script then runs in that editor's session, and the attacker could change content or perform actions with the victim's permissions, for example altering pages that describe or document AI services.

Weaknesses (CWE)

CWE-79Improper Neutralization of Input During Web Page Generation CWE-79Improper Neutralization of Input During Web Page Generation

CWE-79 — Improper Neutralization of Input During Web Page Generation: The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.

[Architecture and Design] Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid [REF-1482]. Examples of libraries and frameworks that make it easier to generate properly encoded output include Microsoft's Anti-XSS library, the OWASP ESAPI Encoding module, and Apache Wicket.
[Implementation, Architecture and Design] Understand the context in which your data will be used and the encoding that will be expected. This is especially important when transmitting data between different components, or when generating outputs that can contain multiple encodings at the same time, such as web pages or multi-part mail messages. Study all expected communication protocols and data representations to determine the required encoding strategies. For any data that will be output to another web page, especially any data that was received from external inputs, use the appropriate encoding on all non-alphanumeric characters. Parts of the same output document may require different encodings, which will vary depending on whether the output is in the: etc. Note that HTML Entity Encoding is only appropriate for the HTML body. Consult the XSS Prevention Cheat Sheet [REF-724] for more details on the types of encoding and escaping that are needed. HTML body Element attributes (such as src="XYZ") URIs JavaScript sections Casca

Source: MITRE CWE corpus.