NVD / CVE Program· CNA ConcreteCMS

CVE-2026-18111: Concrete CMS below 9.5.4 allows privilege escalation because adding users and assigning groups do not require additional identity verification

Noroxi assessment

Priority: Monitor (action score 34/100)

The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
Probability of exploitation in the next 30 days: 0.19% (FIRST EPSS).
Anyone who can reach it over the internet can trigger it. Administrator privileges are required. No special conditions are required; it is repeatable.
According to the record, no fixed version is available yet.

Low priority for now. Update when a fix is released; follow the vendor's advisory.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

Concrete CMS 9 before 9.5.3 was vulnerable to stored cross-site scripting (XSS) in the Feature, Feature Link, Hero Image, and Image blocks and before Concrete 8.5.21 in the feature and Image blocks because the external link URL was insufficiently validated by the link filter and was rendered without output escaping. A user with page-editing permissions (such as Add Block combined with Edit Contents on a single page) could store a crafted external link value that broke out of the link markup and injected arbitrary JavaScript. The script executed in the browser session of any user who subsequently viewed, previewed, or edited the affected page, which could lead to session hijacking and escalation of privileges up to full administrative takeover. The Concrete CMS security team gave this vulnerability a CVSS v4.0 score of 8.5 with vector CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N. Thanks to KhanMarshai for reporting this issue.

HighCVSS 8.5 · v4.0—No exploit No fix recorded

EUVD-2026-78839

Published: Sep 15, 2026
Updated: Oct 15, 2026
EPSS: 0.1% · 8th percentile
CWE: CWE-306

Report tools

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Action score

Monitor

Low priority for now.

CVSS: 34 / 40 · 8.5 / 10
CISA KEV: 0 / 30 · Not listed
EPSS: 0 / 30 · 0.1%

CISA SSVC decision

Exploitation: none
Automatable: no
Technical impact: total

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD: —
CNA · ConcreteCMS: 8.5; NVD has not scored this yet; the score shown is the CNA’s.

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

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Get told when this record changes

Not in KEV: no record of exploitation in the wild
No public exploit code on record
No fixed version yet

If any of these changes, we'll tell you in the daily email digest.

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

Vendor	Product	CPE
concretecms	concrete cms	cpe:2.3:a:concretecms:concrete_cms

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

concretecms concrete cmsbefore 8.5.21
concretecms concrete cms9.0.0 and later · before 9.5.3

Versions reported by the vendor

Affected version ranges reported by the assigning authority (ConcreteCMS). Independent of NVD's CPE analysis and usually ahead of it.

Concrete CMS Concrete CMS
- 9.0.0 and later · up to and including 9.5.2affected · git

Same product

concretecms: all records

Other highest-scoring records for the same primary product.

CVE-2026-6826Concrete 9.5.0 and below has file usage disclosure via missing permission check in Usage controller
60This week
CVE-2022-21829Concrete CMS Versions 9.0.0 through 9.0.2 and 8.5.7 and below can download zip files over HTTP and execute code from those zip files which c
40Plan
CVE-2023-48648Concrete CMS before 8.5.13 and 9.x before 9.2.2 allows unauthorized access because directories can be created with insecure permissions.
39Monitor

Published before and after this one in the same product

← EarlierCVE-2026-81926Sep 15, 2026 · Concrete CMS 9.4.0 through 9.5.2 is vulnerable to Cross-site scripting in the location panel duplicate-path confirmation dialog
8Monitor
← EarlierCVE-2026-81927Sep 15, 2026 · Concrete CMS before 9.5.3 is vulnerable to Stored XSS via SVG upload in "Reject" sanitization mode
7Monitor
Later →CVE-2026-85385Sep 16, 2026 · Concrete CMS below 9.5.4 is vulnerable to Stored XSS via User Timezone Field
30Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

No fix version is recorded for this entry. Check the references for vendor advisories.

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

EPSS, last 120 days

FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

khanmarshaifinder

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

—

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

CVE-2026-818940 days apartConcrete CMS 9.5.2 and below is vulnerable to Stored DOM-based Cross-site Scripting (XSS) in the Gallery block image Caption field
34Monitor
CVE-2026-818950 days apartConcrete CMS 9.5.2 and below is vulnerable to Stored SQL Injection in Concrete CMS Document Library Block via `fsID[]` in `setMode=any`
34Monitor
CVE-2026-184240 days apartConcrete CMS 9.0.0 to 9.5.2 is vulnerable to SSRF protection bypass in remote file import when multiple URLs share a host but use different ports
8Monitor
CVE-2026-819250 days apartConcrete CMS below 9.5.3 is vulnerable to Reflected Cross-Site Scripting (XSS) via Conversation Custom Date Format
8Monitor

Bug bounty scope

Concrete CMSHackerOne · disclosure only (VDP)

The product’s vendor appears in a public program. Matched by name; verify the scope text in the program.

Technical details

Attack conditions

Anyone who can reach it over the internet can trigger it.
Administrator privileges are required.
No special conditions are required; it is repeatable.

If successful

Confidentiality
Integrity
Availability

Attack vector: Network
Attack complexity: Low
Privileges required: High
User interaction: P
Scope: X

Weakness class (CWE)

CWE-306 · Missing Authentication for Critical Function

CVSS vector

CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

nvd-secondary

Root cause

A function added for development or support ships to production without authentication. It often relies on the assumption that it is “only reachable from the internal network.”

The bug in code

The whole CWE-306 class

A representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.

Vulnerable

1// Added for the support team
2app.post("/maintenance/reset", resetDevice);

Fixed

1if (config.maintenanceEnabled) {
2  app.post(
3    "/maintenance/reset",
4    requireSession, requireRole("admin"), resetDevice
5  );
6}

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

Attack patterns (CAPEC)

ATT&CK techniques

—

Change log

No changes recorded on tracked fields yet. Score, KEV, exploit maturity and fix status changes appear here.

References

documentation.concretecms.org/developers/introduction/version-history/953-release-notes

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

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