CVE-2026-81911 Details
Concrete CMS versions 9.0.0 to 9.5.2 is vulnerable to Stored XSS in Board Custom Slot dialog. The custom_slot save_template endpoint authorizes the request only against the target board instance (canEditBoardContents()) and then persists the client-supplied selectedTemplateOption[collection] verbatim, rather than rebuilding the content object collection server-side and verifying that each item belongs to the authorized board's data pool. A user with permission to edit the contents of at least one board instance can therefore store a forged summary object whose description field carries a JavaScript-bearing HTML payload. The default summary template renders the description field without output encoding, so the payload executes in the browser of any user who views the affected board slot, including anonymous front-end visitors and dashboard users who preview the resulting rule or block. This can enable session or action takeover and escalation toward an administrator. Concrete CMS versions below 9 do not include the Boards feature and are not affected. The Concrete CMS security team gave this vulnerability a CVSS v4.0 score of 5.8 with vector CVSS:4.0/AV:N/AC:L/AT:P/PR:H/UI:P/VC:H/VI:L/VA:L/SC:N/SI:N/SA:N. Thanks riodrwn for reporting.
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Exploit prediction scoring system (EPSS) score for CVE-2026-81911
EPSS (Exploit Prediction Scoring System): EPSS predicts the likelihood that a vulnerability will be exploited in the wild. A higher percentage means a greater chance of an exploit occurring. The EPSS model produces a probability score between 0 and 1 (0 and 100%).
0.17 Probability of exploitation activity being observed over the next 30 days (7th percentile)
CVSS score for CVE-2026-81911
CVSS (Common Vulnerability Scoring System): An open framework owned and managed by FIRST.Org, Inc. that assigns a numerical score from 0 to 10 to software vulnerabilities to indicate their severity.
5.4 Medium
Products affected by CVE-2026-81911
ConcreteCMS 9.3.9
ConcreteCMS 9.4.1
ConcreteCMS 9.4.2
ConcreteCMS 9.4.3
ConcreteCMS 9.4.4
DVE Score by Bitsight AI
DVE scores complement traditional static scoring systems like CVSS with Bitsight AI powered real-time threat intelligence and underground cyber criminal activity so that security teams can reduce alert fatigue and focus on vulnerabilities most likely to be exploited.
Low
More on DVE scores

CVE-2026-81911 Global Footprint

Top 10 Identified Countries

Country Observations Percentage
US 100 60.61%
DE 22 13.33%
JP 12 7.27%
GB 6 3.64%
NL 6 3.64%
TR 5 3.03%
IE 3 1.82%
PL 3 1.82%
AT 2 1.21%
FR 2 1.21%

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CVE-2026-81911 Industry Footprint

Top 10 Identified Industries

*Service provider organizations (typically Technology and Telecommunications) are disproportionally represented in the results given their upstream ownership of end-user infrastructure. See our FAQs.

Industry* Observations Percentage
Technology 149 93.13%
Telecommunications 4 2.50%
Education 3 1.88%
Business Services 2 1.25%
Government/Politics 1 0.63%
Finance 1 0.63%

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