Vulnerability-Lookup

FKIE_CVE-2026-8135

Vulnerability from fkie_nvd - Published: 2026-05-21 21:16 - Updated: 2026-05-26 18:44

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

{
  "configurations": [
    {
      "nodes": [
        {
          "cpeMatch": [
            {
              "criteria": "cpe:2.3:a:concretecms:concrete_cms:*:*:*:*:*:*:*:*",
              "matchCriteriaId": "435732F0-BA4B-4432-97EA-B730EBD44D4D",
              "versionEndIncluding": "9.5.0",
              "vulnerable": true
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  "descriptions": [
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      "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"
    }
  ],
  "id": "CVE-2026-8135",
  "lastModified": "2026-05-26T18:44:04.753",
  "metrics": {
    "cvssMetricV31": [
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        "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"
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        "impactScore": 5.9,
        "source": "nvd@nist.gov",
        "type": "Primary"
      }
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    "cvssMetricV40": [
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          "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",
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          "vulnIntegrityImpact": "HIGH",
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        "type": "Secondary"
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  "references": [
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  "sourceIdentifier": "ff5b8ace-8b95-4078-9743-eac1ca5451de",
  "vulnStatus": "Analyzed",
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      "type": "Secondary"
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  ]
}

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 (v2.0.3)

CWE

CWE-502 - Deserialization of untrusted data

Assigner

ConcreteCMS

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

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                "role": "CISA Coordinator",
                "timestamp": "2026-05-22T12:14:43.741857Z",
                "version": "2.0.3"
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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.

Action not permitted

FKIE_CVE-2026-8135

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

Tags

Sightings

Nomenclature