CVE-2026-81911Network attack vectorHinoki check available

Stored XSS via unescaped board summary descriptions

Published Sep 11, 2026 · Updated Sep 11, 2026

Stored XSS in the Board Custom Slot dialog in Concrete CMS 9.0.0 through 9.5.2 allows remote authenticated users to execute script. The custom_slot save_template endpoint stores a client-supplied collection without verifying board membership, and the default summary template renders its description without output encoding. Board-content editing permission is required; forged summary HTML then executes for visitors or dashboard users who view the slot, enabling session or action takeover.

CVSS severity5.8
Medium
EPSS probability0.30%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkAvailable
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Summary

What happened

Stored XSS in the Board Custom Slot dialog in Concrete CMS 9.0.0 through 9.5.2 allows remote authenticated users to execute script. The custom_slot save_template endpoint stores a client-supplied collection without verifying board membership, and the default summary template renders its description without output encoding. Board-content editing permission is required; forged summary HTML then executes for visitors or dashboard users who view the slot, enabling session or action takeover.

The record

CVE
CVE-2026-81911
Published
Sep 11, 2026
Updated
Sep 11, 2026
Vendor
Concrete CMS
Product
Concrete CMS
Classifications
T1189
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Sep 11, 2026CVE publishedPublication date reported by the CVE source.
  2. Sep 11, 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=9.0.0 <=9.5.2

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Concrete CMS · Concrete CMSversion=9.0.0 <=9.5.2

Published CVSS scores

5.8Concrete CMS security teamCVSS:4.0/AV:N/AC:L/AT:P/PR:H/UI:P/VC:H/VI:L/VA:L/SC:N/SI:N/SA:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

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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 exploitUnconfirmed

Weakness, pattern, technique

T1189Drive-by Compromise

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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