Vulnerability-Lookup

CVE-2026-81900 (GCVE-0-2026-81900)

Vulnerability from cvelistv5 – Published: 2026-09-14 22:07 – Updated: 2026-09-15 13:44

Title

Concrete CMS before 9.5.3 is vulnerable to Stored XSS in the YouTube block (vWidth/vHeight)

Summary

Concrete CMS before 9.5.3 applied only trim() to the YouTube block's stored width and height values and printed them into iframe HTML attributes without escaping or integer casting, resulting in stored cross-site scripting. A user with edit_block permission could inject an event handler that executed script for visitors rendering the page, acting with administrative privileges where the victim was an administrator. The Concrete CMS security team gave this vulnerability a CVSS v4.0 score of 7.3 with vector CVSS:4.0/AV:N/AC:L/AT:P/PR:H/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N. Thanks sh4d0byss for reporting.

Severity

7.3 (High)


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

SSVC

Exploitation: none Automatable: no Technical Impact: total

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-09-15 13:44 UTC

CWE

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

Assigner

ConcreteCMS mitre root

References

1 reference

URL	Tags
https://documentation.concretecms.org/developers/…	release-notes

Impacted products

1 product

Vendor	Product	Version	CPE status
Concrete CMS	Concrete CMS	Affected: 5.0.0 , ≤ 9.5.2 (git)	guessed

Credits

sh4d0byss

Show details on NVD website

JSON

To clipboard

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FKIE_CVE-2026-81900

Vulnerability from fkie_nvd - Published: 2026-09-14 23:18 - Updated: 2026-09-15 14:40

Severity

7.3 (High) - CVSS:4.0/AV:N/AC:L/AT:P/PR:H/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

Summary

References

	URL	Tags
	ff5b8ace-8b95-4078-9743-eac1ca5451de	https://documentation.concretecms.org/developers/introduction/version-history/953-release-notes

Impacted products

	Vendor	Product	Version

JSON

To clipboard

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  ],
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GHSA-C87M-38HC-RC4G

Vulnerability from github – Published: 2026-09-15 00:31 – Updated: 2026-09-15 00:31

Details

Severity

7.3 (High)


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

Show details on source website

JSON

To clipboard

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    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-09-14T23:18:48Z",
    "severity": "HIGH"
  },
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  "id": "GHSA-c87m-38hc-rc4g",
  "modified": "2026-09-15T00:31:14Z",
  "published": "2026-09-15T00:31:14Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-81900"
    },
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      "url": "https://documentation.concretecms.org/developers/introduction/version-history/953-release-notes"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:P/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",
      "type": "CVSS_V4"
    }
  ]
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.

Related by attack behaviour

Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.

Action not permitted

CVE-2026-81900 (GCVE-0-2026-81900)

FKIE_CVE-2026-81900

GHSA-C87M-38HC-RC4G

Tags

Sightings

Nomenclature

Related by attack behaviour