Vulnerability-Lookup

FKIE_CVE-2026-8135

Vulnerability from fkie_nvd - Published: 2026-05-21 21:16 - Updated: 2026-07-23 16:10

Severity

7.2 (High) - CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H

Summary

Concrete CMS 9.5.0 and below is vulnerable to Remote Code Execution due to insecure deserialization occurring in the ExpressEntryList block controller. An rogue administrator with privileges to add blocks to an area can bypass the intended protection mechanism (_fromCIF === true), which normally restricts malicious inputs over form POST requests, by leveraging the REST API functionality. Because the REST API parses requests using json_decode(), the string "true" is evaluated as a strict PHP Boolean(true). This bypass allows the attacker to inject a malicious serialized payload into the block's filterFields database column. The payload will subsequently be executed when the block's data is viewed or edited by an administrator leading to complete server takeover (RCE).The Concrete CMS security team gave this vulnerability a CVSS v.4.0 score of 8.9 with a vector of CVSS:4.0/AV:N/AC:H/AT:P/PR:H/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H. Thanks Nguyễn Văn Thiện https://github.com/Thien225409 for reporting

References

	URL	Tags
	ff5b8ace-8b95-4078-9743-eac1ca5451de	https://documentation.concretecms.org/9-x/developers/introduction/version-history/951-release-notes	Release Notes

Impacted products

	Vendor	Product	Version
	concretecms	concrete_cms	*

JSON

To clipboard

{
  "affected": [
    {
      "affectedData": [
        {
          "collectionURL": "https://github.com/concretecms/concretecms",
          "defaultStatus": "unaffected",
          "product": "Concrete CMS",
          "repo": "https://github.com/concretecms/concretecms",
          "vendor": "Concrete CMS",
          "versions": [
            {
              "lessThanOrEqual": "9.5.0",
              "status": "affected",
              "version": "5.0",
              "versionType": "git"
            }
          ]
        }
      ],
      "source": "ff5b8ace-8b95-4078-9743-eac1ca5451de"
    }
  ],
  "configurations": [
    {
      "nodes": [
        {
          "cpeMatch": [
            {
              "criteria": "cpe:2.3:a:concretecms:concrete_cms:*:*:*:*:*:*:*:*",
              "matchCriteriaId": "435732F0-BA4B-4432-97EA-B730EBD44D4D",
              "versionEndIncluding": "9.5.0",
              "vulnerable": true
            }
          ],
          "negate": false,
          "operator": "OR"
        }
      ]
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "Concrete CMS 9.5.0 and below is vulnerable to Remote Code Execution  due to insecure deserialization occurring in the\u00a0ExpressEntryList\u00a0block controller. An rogue administrator with privileges to add blocks to an area can bypass the intended protection mechanism (_fromCIF === true), which normally restricts malicious inputs over form POST requests, by leveraging the REST API functionality. Because the REST API parses requests using json_decode(), the string \"true\" is evaluated as a strict PHP Boolean(true).\u00a0 This bypass allows the attacker to inject a malicious serialized payload \u00a0into the block\u0027s filterFields database column. The payload will subsequently be executed when the block\u0027s data is viewed or edited by an administrator leading to complete server takeover (RCE).The Concrete CMS security team gave this vulnerability a CVSS v.4.0 score of 8.9 with a vector of\u00a0CVSS:4.0/AV:N/AC:H/AT:P/PR:H/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H.\u00a0 Thanks  Nguy\u1ec5n V\u0103n Thi\u1ec7n https://github.com/Thien225409 \u00a0for reporting"
    },
    {
      "lang": "es",
      "value": "Concrete CMS 9.5.0 y versiones anteriores es vulnerable a la ejecuci\u00f3n remota de c\u00f3digo debido a la deserializaci\u00f3n insegura que ocurre en el controlador de bloque ExpressEntryList. Un administrador malintencionado con privilegios para a\u00f1adir bloques a un \u00e1rea puede eludir el mecanismo de protecci\u00f3n previsto (_fromCIF === true), que normalmente restringe las entradas maliciosas a trav\u00e9s de solicitudes POST de formulario, aprovechando la funcionalidad de la API REST. Debido a que la API REST analiza las solicitudes usando json_decode(), la cadena \u0027true\u0027 se eval\u00faa como un booleano PHP estricto (true). Esta elusi\u00f3n permite al atacante inyectar una carga \u00fatil serializada maliciosa en la columna de la base de datos filterFields del bloque. La carga \u00fatil se ejecutar\u00e1 posteriormente cuando los datos del bloque sean vistos o editados por un administrador, lo que lleva a la toma de control completa del servidor (RCE). El equipo de seguridad de Concrete CMS otorg\u00f3 a esta vulnerabilidad una puntuaci\u00f3n CVSS v.4.0 de 8.9 con un vector de CVSS:4.0/AV:N/AC:H/AT:P/PR:H/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H. Gracias a Nguy?n V?n Thi?n https://github.com/Thien225409 por informar."
    }
  ],
  "id": "CVE-2026-8135",
  "lastModified": "2026-07-23T16:10:00.137",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "LOW",
          "attackVector": "NETWORK",
          "availabilityImpact": "HIGH",
          "baseScore": 7.2,
          "baseSeverity": "HIGH",
          "confidentialityImpact": "HIGH",
          "integrityImpact": "HIGH",
          "privilegesRequired": "HIGH",
          "scope": "UNCHANGED",
          "userInteraction": "NONE",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H",
          "version": "3.1"
        },
        "exploitabilityScore": 1.2,
        "impactScore": 5.9,
        "source": "nvd@nist.gov",
        "type": "Primary"
      }
    ],
    "cvssMetricV40": [
      {
        "cvssData": {
          "Automatable": "NOT_DEFINED",
          "Recovery": "NOT_DEFINED",
          "Safety": "NOT_DEFINED",
          "attackComplexity": "HIGH",
          "attackRequirements": "PRESENT",
          "attackVector": "NETWORK",
          "availabilityRequirement": "NOT_DEFINED",
          "baseScore": 8.9,
          "baseSeverity": "HIGH",
          "confidentialityRequirement": "NOT_DEFINED",
          "exploitMaturity": "NOT_DEFINED",
          "integrityRequirement": "NOT_DEFINED",
          "modifiedAttackComplexity": "NOT_DEFINED",
          "modifiedAttackRequirements": "NOT_DEFINED",
          "modifiedAttackVector": "NOT_DEFINED",
          "modifiedPrivilegesRequired": "NOT_DEFINED",
          "modifiedSubAvailabilityImpact": "NOT_DEFINED",
          "modifiedSubConfidentialityImpact": "NOT_DEFINED",
          "modifiedSubIntegrityImpact": "NOT_DEFINED",
          "modifiedUserInteraction": "NOT_DEFINED",
          "modifiedVulnAvailabilityImpact": "NOT_DEFINED",
          "modifiedVulnConfidentialityImpact": "NOT_DEFINED",
          "modifiedVulnIntegrityImpact": "NOT_DEFINED",
          "privilegesRequired": "HIGH",
          "providerUrgency": "NOT_DEFINED",
          "subAvailabilityImpact": "HIGH",
          "subConfidentialityImpact": "HIGH",
          "subIntegrityImpact": "HIGH",
          "userInteraction": "NONE",
          "valueDensity": "NOT_DEFINED",
          "vectorString": "CVSS:4.0/AV:N/AC:H/AT:P/PR:H/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H/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",
          "version": "4.0",
          "vulnAvailabilityImpact": "HIGH",
          "vulnConfidentialityImpact": "HIGH",
          "vulnIntegrityImpact": "HIGH",
          "vulnerabilityResponseEffort": "NOT_DEFINED"
        },
        "source": "ff5b8ace-8b95-4078-9743-eac1ca5451de",
        "type": "Secondary"
      }
    ],
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "id": "CVE-2026-8135",
          "options": [
            {
              "exploitation": "none"
            },
            {
              "automatable": "no"
            },
            {
              "technicalImpact": "total"
            }
          ],
          "role": "CISA Coordinator",
          "timestamp": "2026-05-22T12:14:43.741857Z",
          "version": "2.0.3"
        }
      }
    ]
  },
  "published": "2026-05-21T21:16:32.970",
  "references": [
    {
      "source": "ff5b8ace-8b95-4078-9743-eac1ca5451de",
      "tags": [
        "Release Notes"
      ],
      "url": "https://documentation.concretecms.org/9-x/developers/introduction/version-history/951-release-notes"
    }
  ],
  "sourceIdentifier": "ff5b8ace-8b95-4078-9743-eac1ca5451de",
  "vulnStatus": "Analyzed",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-502"
        }
      ],
      "source": "ff5b8ace-8b95-4078-9743-eac1ca5451de",
      "type": "Secondary"
    }
  ]
}

CVE-2026-8135 (GCVE-0-2026-8135)

Vulnerability from cvelistv5 – Published: 2026-05-21 20:16 – Updated: 2026-05-22 12:14

Title

Concrete CMS 9.5.0 and below is vulnerable to RCE due to insecure deserialization occurring in the ExpressEntryList block controller.

Summary

Severity

8.9 (High)


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

SSVC

Exploitation: none Automatable: no Technical Impact: total

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-05-22 12:14 UTC

CWE

CWE-502 - Deserialization of untrusted data

Assigner

ConcreteCMS mitre root

References

1 reference

URL	Tags
https://documentation.concretecms.org/9-x/develop…	release-notes

Impacted products

1 product

Vendor	Product	Version
Concrete CMS	Concrete CMS	Affected: 5.0 , ≤ 9.5.0 (git)

Credits

Nguyễn Văn Thiện

Show details on NVD website

JSON

To clipboard

{
  "containers": {
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        "metrics": [
          {
            "other": {
              "content": {
                "id": "CVE-2026-8135",
                "options": [
                  {
                    "Exploitation": "none"
                  },
                  {
                    "Automatable": "no"
                  },
                  {
                    "Technical Impact": "total"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-05-22T12:14:43.741857Z",
                "version": "2.0.3"
              },
              "type": "ssvc"
            }
          }
        ],
        "providerMetadata": {
          "dateUpdated": "2026-05-22T12:14:52.431Z",
          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
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      }
    ],
    "cna": {
      "affected": [
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          "collectionURL": "https://github.com/concretecms/concretecms",
          "defaultStatus": "unaffected",
          "product": "Concrete CMS",
          "repo": "https://github.com/concretecms/concretecms",
          "vendor": "Concrete CMS",
          "versions": [
            {
              "lessThanOrEqual": "9.5.0",
              "status": "affected",
              "version": "5.0",
              "versionType": "git"
            }
          ]
        }
      ],
      "credits": [
        {
          "lang": "en",
          "type": "finder",
          "value": "Nguy\u1ec5n V\u0103n Thi\u1ec7n"
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "supportingMedia": [
            {
              "base64": false,
              "type": "text/html",
              "value": "Concrete CMS 9.5.0 and below is vulnerable to Remote Code Execution  due to insecure deserialization occurring in the\u0026nbsp;\u003ccode\u003eExpressEntryList\u003c/code\u003e\u0026nbsp;block controller. An rogue administrator with privileges to add blocks to an area can bypass the intended protection mechanism (\u003ccode\u003e_fromCIF === true\u003c/code\u003e), which normally restricts malicious inputs over form POST requests, by leveraging the REST API functionality. Because the REST API parses requests using \u003ccode\u003ejson_decode()\u003c/code\u003e, the string \u003ccode\u003e\"true\"\u003c/code\u003e is evaluated as a strict PHP \u003ccode\u003eBoolean(true)\u003c/code\u003e.\u0026nbsp; This bypass allows the attacker to inject a malicious serialized payload \u0026nbsp;into the block\u0027s \u003ccode\u003efilterFields\u003c/code\u003e database column. The payload will subsequently be executed when the block\u0027s data is viewed or edited by an administrator leading to complete server takeover (RCE).The Concrete CMS security team gave this vulnerability a CVSS v.4.0 score of 8.9 with a vector of\u0026nbsp;CVSS:4.0/AV:N/AC:H/AT:P/PR:H/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H.\u0026nbsp; Thanks \u003ca href=\"https://github.com/Thien225409\"\u003eNguy\u1ec5n V\u0103n Thi\u1ec7n\u003c/a\u003e\u0026nbsp;for reporting\u0026nbsp;"
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      "impacts": [
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          "capecId": "CAPEC-116",
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          "capecId": "CAPEC-586",
          "descriptions": [
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              "lang": "en",
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      "metrics": [
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          "cvssV4_0": {
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            "Recovery": "NOT_DEFINED",
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            "vulnAvailabilityImpact": "HIGH",
            "vulnConfidentialityImpact": "HIGH",
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            "vulnerabilityResponseEffort": "NOT_DEFINED"
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        "orgId": "ff5b8ace-8b95-4078-9743-eac1ca5451de",
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          "tags": [
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          "url": "https://documentation.concretecms.org/9-x/developers/introduction/version-history/951-release-notes"
        }
      ],
      "source": {
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        "discovery": "EXTERNAL"
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    "datePublished": "2026-05-21T20:16:39.866Z",
    "dateReserved": "2026-05-07T17:54:13.820Z",
    "dateUpdated": "2026-05-22T12:14:52.431Z",
    "state": "PUBLISHED"
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  "dataType": "CVE_RECORD",
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}

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.

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FKIE_CVE-2026-8135

CVE-2026-8135 (GCVE-0-2026-8135)

Tags

Sightings

Nomenclature