Vulnerability-Lookup

GHSA-R8F2-FXJR-GX5R

Vulnerability from github – Published: 2026-10-27 15:32 – Updated: 2026-10-27 15:32

Details

Umbraco CMS before 17.7.2 and 18.2.2 contains an authentication bypass vulnerability that allows unauthenticated attackers to register attacker-controlled OAuth redirect URIs by poisoning the Host header. Attackers send signed-in users authorization links using response_mode=form_post to capture codes, then redeem them via HTTP Basic client credentials to hijack back-office sessions and execute code through Razor templates.

Severity

7.5 (High)


                  
                    CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H

7.7 (High)


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

Show details on source website

JSON

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{
  "affected": [],
  "aliases": [
    "CVE-2026-117553"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-601"
    ],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-10-27T14:16:35Z",
    "severity": "HIGH"
  },
  "details": "Umbraco CMS before 17.7.2 and 18.2.2 contains an authentication bypass vulnerability that allows unauthenticated attackers to register attacker-controlled OAuth redirect URIs by poisoning the Host header. Attackers send signed-in users authorization links using response_mode=form_post to capture codes, then redeem them via HTTP Basic client credentials to hijack back-office sessions and execute code through Razor templates.",
  "id": "GHSA-r8f2-fxjr-gx5r",
  "modified": "2026-10-27T15:32:43Z",
  "published": "2026-10-27T15:32:43Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/umbraco/Umbraco-CMS/security/advisories/GHSA-rpv9-qp4c-g469"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-117553"
    },
    {
      "type": "WEB",
      "url": "https://github.com/umbraco/Umbraco-CMS/commit/490b9b27dcbb8fb3fe868a36203590968b0569d6"
    },
    {
      "type": "WEB",
      "url": "https://github.com/umbraco/Umbraco-CMS"
    },
    {
      "type": "WEB",
      "url": "https://github.com/umbraco/Umbraco-CMS/blob/release-18.2.1/src/Umbraco.Cms.Api.Management/Middleware/BackOfficeAuthorizationInitializationMiddleware.cs#L74-L112"
    },
    {
      "type": "WEB",
      "url": "https://www.vulncheck.com/advisories/umbraco-cms-before-17.7.2-and-18.2.2-account-takeover-via-host-header-poisoning"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H",
      "type": "CVSS_V3"
    },
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/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"
    }
  ]
}

CVE-2026-117553 (GCVE-0-2026-117553)

Vulnerability from cvelistv5 – Published: 2026-10-27 13:07 – Updated: 2026-10-27 13:07

Title

Umbraco CMS before 17.7.2 and 18.2.2 Account Takeover via Host Header Poisoning

Summary

Severity

7.7 (High)


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

7.5 (High)


                        
                          CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H

CWE

CWE-601 - URL Redirection to Untrusted Site ('Open Redirect')

Assigner

VulnCheck CNA under the mitre root

CNA scorecard B 84/100 over 7152 records in the last 180 days details

References

5 references

URL	Tags
https://github.com/umbraco/Umbraco-CMS/commit/490…	patch
https://github.com/umbraco/Umbraco-CMS	product
https://github.com/umbraco/Umbraco-CMS/security/a…	vendor-advisory
https://github.com/umbraco/Umbraco-CMS/blob/relea…	technical-description
https://www.vulncheck.com/advisories/umbraco-cms-…	third-party-advisory

Impacted products

1 product

Vendor	Product	Version
umbraco	Umbraco-CMS	Affected: 0 , < 17.7.2 (semver) Affected: 18.0.0 , < 18.2.2 (semver) cpe:2.3:a:umbraco:umbraco_cms:::::::: cpe:2.3:a:umbraco:umbraco_cms::::::::

Date Public

2026-10-27 00:00

Credits

Eu Joe Chegne (Project Umbra) Damien Wong (Project Umbra) AndyButland

Show details on NVD website

JSON

To clipboard

{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "packageURL": "pkg:nuget/Umbraco.Cms",
          "product": "Umbraco-CMS",
          "vendor": "umbraco",
          "versions": [
            {
              "lessThan": "17.7.2",
              "status": "affected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThan": "18.2.2",
              "status": "affected",
              "version": "18.0.0",
              "versionType": "semver"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:a:umbraco:umbraco_cms:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "17.7.2",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:a:umbraco:umbraco_cms:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "18.2.2",
                  "versionStartIncluding": "18.0.0",
                  "vulnerable": true
                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "credits": [
        {
          "lang": "en",
          "type": "finder",
          "value": "Eu Joe Chegne (Project Umbra)"
        },
        {
          "lang": "en",
          "type": "finder",
          "value": "Damien Wong (Project Umbra)"
        },
        {
          "lang": "en",
          "type": "remediation developer",
          "value": "AndyButland"
        }
      ],
      "datePublic": "2026-10-27T00:00:00.000Z",
      "descriptions": [
        {
          "lang": "en",
          "value": "Umbraco CMS before 17.7.2 and 18.2.2 contains an authentication bypass vulnerability that allows unauthenticated attackers to register attacker-controlled OAuth redirect URIs by poisoning the Host header. Attackers send signed-in users authorization links using response_mode=form_post to capture codes, then redeem them via HTTP Basic client credentials to hijack back-office sessions and execute code through Razor templates."
        }
      ],
      "metrics": [
        {
          "cvssV4_0": {
            "attackComplexity": "LOW",
            "attackRequirements": "PRESENT",
            "attackVector": "NETWORK",
            "baseScore": 7.7,
            "baseSeverity": "HIGH",
            "privilegesRequired": "NONE",
            "subAvailabilityImpact": "NONE",
            "subConfidentialityImpact": "NONE",
            "subIntegrityImpact": "NONE",
            "userInteraction": "PASSIVE",
            "vectorString": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N",
            "version": "4.0",
            "vulnAvailabilityImpact": "HIGH",
            "vulnConfidentialityImpact": "HIGH",
            "vulnIntegrityImpact": "HIGH"
          },
          "format": "CVSS"
        },
        {
          "cvssV3_1": {
            "attackComplexity": "HIGH",
            "attackVector": "NETWORK",
            "availabilityImpact": "HIGH",
            "baseScore": 7.5,
            "baseSeverity": "HIGH",
            "confidentialityImpact": "HIGH",
            "integrityImpact": "HIGH",
            "privilegesRequired": "NONE",
            "scope": "UNCHANGED",
            "userInteraction": "REQUIRED",
            "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H",
            "version": "3.1"
          },
          "format": "CVSS"
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-601",
              "description": "URL Redirection to Untrusted Site (\u0027Open Redirect\u0027)",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-27T13:07:49.671Z",
        "orgId": "83251b91-4cc7-4094-a5c7-464a1b83ea10",
        "shortName": "VulnCheck"
      },
      "references": [
        {
          "name": "Patch Commit",
          "tags": [
            "patch"
          ],
          "url": "https://github.com/umbraco/Umbraco-CMS/commit/490b9b27dcbb8fb3fe868a36203590968b0569d6"
        },
        {
          "tags": [
            "product"
          ],
          "url": "https://github.com/umbraco/Umbraco-CMS"
        },
        {
          "name": "GitHub Security Advisory (GHSA-rpv9-qp4c-g469)",
          "tags": [
            "vendor-advisory"
          ],
          "url": "https://github.com/umbraco/Umbraco-CMS/security/advisories/GHSA-rpv9-qp4c-g469"
        },
        {
          "tags": [
            "technical-description"
          ],
          "url": "https://github.com/umbraco/Umbraco-CMS/blob/release-18.2.1/src/Umbraco.Cms.Api.Management/Middleware/BackOfficeAuthorizationInitializationMiddleware.cs#L74-L112"
        },
        {
          "name": "VulnCheck Advisory: Umbraco CMS before 17.7.2 and 18.2.2 Account Takeover via Host Header Poisoning",
          "tags": [
            "third-party-advisory"
          ],
          "url": "https://www.vulncheck.com/advisories/umbraco-cms-before-17.7.2-and-18.2.2-account-takeover-via-host-header-poisoning"
        }
      ],
      "title": "Umbraco CMS before 17.7.2 and 18.2.2 Account Takeover via Host Header Poisoning",
      "x_generator": {
        "engine": "vulncheck-endgame"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "83251b91-4cc7-4094-a5c7-464a1b83ea10",
    "assignerShortName": "VulnCheck",
    "cveId": "CVE-2026-117553",
    "datePublished": "2026-10-27T13:07:49.671Z",
    "dateReserved": "2026-10-27T11:25:13.186Z",
    "dateUpdated": "2026-10-27T13:07:49.671Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}

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.

Vulnerability timeline

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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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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.

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