CWE-939

Improper Authorization in Handler for Custom URL Scheme

The product uses a handler for a custom URL scheme, but it does not properly restrict which actors can invoke the handler using the scheme.

CVE-2026-33335 (GCVE-0-2026-33335)

Vulnerability from cvelistv5 – Published: 2026-03-24 15:07 – Updated: 2026-03-25 13:41
VLAI
Title
Vikunja Desktop allows arbitrary local application invocation via unvalidated shell.openExternal
Summary
Vikunja is an open-source self-hosted task management platform. Starting in version 0.21.0 and prior to version 2.2.0, the Vikunja Desktop Electron wrapper passes URLs from `window.open()` calls directly to `shell.openExternal()` without any validation or protocol allowlisting. An attacker who can place a link with `target="_blank"` (or that otherwise triggers `window.open`) in user-generated content can cause the victim's operating system to open arbitrary URI schemes, invoking local applications, opening local files, or triggering custom protocol handlers. Version 2.2.0 patches the issue.
Severity
6.4 (Medium)
CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:N/VI:N/VA:N/SC:H/SI:H/SA:H
CWE
  • CWE-939 - Improper Authorization in Handler for Custom URL Scheme
Assigner
References
Impacted products
Vendor Product Version
go-vikunja vikunja Affected: >= 0.21.0, < 2.2.0
Create a notification for this product.
Show details on NVD website
To clipboard 

{
  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "other": {
              "content": {
                "id": "CVE-2026-33335",
                "options": [
                  {
                    "Exploitation": "poc"
                  },
                  {
                    "Automatable": "no"
                  },
                  {
                    "Technical Impact": "partial"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-03-25T13:41:45.712476Z",
                "version": "2.0.3"
              },
              "type": "ssvc"
            }
          }
        ],
        "providerMetadata": {
          "dateUpdated": "2026-03-25T13:41:50.096Z",
          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
        "references": [
          {
            "tags": [
              "exploit"
            ],
            "url": "https://github.com/go-vikunja/vikunja/security/advisories/GHSA-6q44-85gc-cjvf"
          }
        ],
        "title": "CISA ADP Vulnrichment"
      }
    ],
    "cna": {
      "affected": [
        {
          "product": "vikunja",
          "vendor": "go-vikunja",
          "versions": [
            {
              "status": "affected",
              "version": "\u003e= 0.21.0, \u003c 2.2.0"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "Vikunja is an open-source self-hosted task management platform. Starting in version 0.21.0 and prior to version 2.2.0, the Vikunja Desktop Electron wrapper passes URLs from `window.open()` calls directly to `shell.openExternal()` without any validation or protocol allowlisting. An attacker who can place a link with `target=\"_blank\"` (or that otherwise triggers `window.open`) in user-generated content can cause the victim\u0027s operating system to open arbitrary URI schemes, invoking local applications, opening local files, or triggering custom protocol handlers. Version 2.2.0 patches the issue."
        }
      ],
      "metrics": [
        {
          "cvssV4_0": {
            "attackComplexity": "LOW",
            "attackRequirements": "NONE",
            "attackVector": "NETWORK",
            "baseScore": 6.4,
            "baseSeverity": "MEDIUM",
            "privilegesRequired": "LOW",
            "subAvailabilityImpact": "HIGH",
            "subConfidentialityImpact": "HIGH",
            "subIntegrityImpact": "HIGH",
            "userInteraction": "PASSIVE",
            "vectorString": "CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:N/VI:N/VA:N/SC:H/SI:H/SA:H",
            "version": "4.0",
            "vulnAvailabilityImpact": "NONE",
            "vulnConfidentialityImpact": "NONE",
            "vulnIntegrityImpact": "NONE"
          }
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-939",
              "description": "CWE-939: Improper Authorization in Handler for Custom URL Scheme",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-03-24T15:07:41.460Z",
        "orgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
        "shortName": "GitHub_M"
      },
      "references": [
        {
          "name": "https://github.com/go-vikunja/vikunja/security/advisories/GHSA-6q44-85gc-cjvf",
          "tags": [
            "x_refsource_CONFIRM"
          ],
          "url": "https://github.com/go-vikunja/vikunja/security/advisories/GHSA-6q44-85gc-cjvf"
        },
        {
          "name": "https://vikunja.io/changelog/vikunja-v2.2.0-was-released",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://vikunja.io/changelog/vikunja-v2.2.0-was-released"
        }
      ],
      "source": {
        "advisory": "GHSA-6q44-85gc-cjvf",
        "discovery": "UNKNOWN"
      },
      "title": "Vikunja Desktop allows arbitrary local application invocation via unvalidated shell.openExternal"
    }
  },
  "cveMetadata": {
    "assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
    "assignerShortName": "GitHub_M",
    "cveId": "CVE-2026-33335",
    "datePublished": "2026-03-24T15:07:41.460Z",
    "dateReserved": "2026-03-18T22:15:11.812Z",
    "dateUpdated": "2026-03-25T13:41:50.096Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}

CVE-2026-3471 (GCVE-0-2026-3471)

Vulnerability from cvelistv5 – Published: 2026-05-18 08:45 – Updated: 2026-05-18 14:35
VLAI
Title
Opening a window with {{javascript:alert()}} as URL causes crash in the Mattermost Desktop App
Summary
Mattermost Desktop App versions <=6.1 6.0.1 5.4.13.0 fail to prevent an invalid URL from loading in a pop-up window in the Mattermost Desktop App which allows a malicious server owner to repeated crash the application via calling {{window.open('javascript:alert()');}}. Mattermost Advisory ID: MMSA-2026-00618
Severity
6.5 (Medium)
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
CWE
  • CWE-939 - Improper Authorization in Handler for Custom URL Scheme
Assigner
References
URL Tags
https://mattermost.com/security-updates vendor-advisory
Impacted products
Vendor Product Version
Mattermost Mattermost Affected: 0 , ≤ 6.0.1 (semver)
Affected: 0 , ≤ 5.4.13 (semver)
Unaffected: 6.2.0
Unaffected: 6.1.1.0
Unaffected: 5.13.5.0
Create a notification for this product.
Credits
game0v3r
Show details on NVD website
To clipboard 

{
  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "other": {
              "content": {
                "id": "CVE-2026-3471",
                "options": [
                  {
                    "Exploitation": "none"
                  },
                  {
                    "Automatable": "no"
                  },
                  {
                    "Technical Impact": "partial"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-05-18T14:34:41.218853Z",
                "version": "2.0.3"
              },
              "type": "ssvc"
            }
          }
        ],
        "providerMetadata": {
          "dateUpdated": "2026-05-18T14:35:23.933Z",
          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
        "title": "CISA ADP Vulnrichment"
      }
    ],
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Mattermost",
          "vendor": "Mattermost",
          "versions": [
            {
              "lessThanOrEqual": "6.0.1",
              "status": "affected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "5.4.13",
              "status": "affected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "status": "unaffected",
              "version": "6.2.0"
            },
            {
              "status": "unaffected",
              "version": "6.1.1.0"
            },
            {
              "status": "unaffected",
              "version": "5.13.5.0"
            }
          ]
        }
      ],
      "credits": [
        {
          "lang": "en",
          "type": "finder",
          "value": "game0v3r"
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "Mattermost Desktop App versions \u003c=6.1 6.0.1 5.4.13.0 fail to prevent an invalid URL from loading in a pop-up window in the Mattermost Desktop App which allows a malicious server owner to repeated crash the application via calling {{window.open(\u0027javascript:alert()\u0027);}}. Mattermost Advisory ID: MMSA-2026-00618"
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "attackComplexity": "LOW",
            "attackVector": "NETWORK",
            "availabilityImpact": "HIGH",
            "baseScore": 6.5,
            "baseSeverity": "MEDIUM",
            "confidentialityImpact": "NONE",
            "integrityImpact": "NONE",
            "privilegesRequired": "NONE",
            "scope": "UNCHANGED",
            "userInteraction": "REQUIRED",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H",
            "version": "3.1"
          },
          "format": "CVSS",
          "scenarios": [
            {
              "lang": "en",
              "value": "GENERAL"
            }
          ]
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-939",
              "description": "CWE-939: Improper Authorization in Handler for Custom URL Scheme",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-05-18T08:45:44.576Z",
        "orgId": "9302f53e-dde5-4bf3-b2f2-a83f91ac0eee",
        "shortName": "Mattermost"
      },
      "references": [
        {
          "name": "MMSA-2026-00618",
          "tags": [
            "vendor-advisory"
          ],
          "url": "https://mattermost.com/security-updates"
        }
      ],
      "solutions": [
        {
          "lang": "en",
          "value": "Update Mattermost Desktop App to versions 6.2.0, 6.1.1.0, 5.13.5.0 or higher."
        }
      ],
      "source": {
        "advisory": "MMSA-2026-00618",
        "defect": [
          "https://mattermost.atlassian.net/browse/MM-67756"
        ],
        "discovery": "EXTERNAL"
      },
      "title": "Opening a window with {{javascript:alert()}} as URL causes crash in the Mattermost Desktop App",
      "x_generator": {
        "engine": "cvelib 1.8.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "9302f53e-dde5-4bf3-b2f2-a83f91ac0eee",
    "assignerShortName": "Mattermost",
    "cveId": "CVE-2026-3471",
    "datePublished": "2026-05-18T08:45:44.576Z",
    "dateReserved": "2026-03-03T10:41:41.370Z",
    "dateUpdated": "2026-05-18T14:35:23.933Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}

CVE-2026-35394 (GCVE-0-2026-35394)

Vulnerability from cvelistv5 – Published: 2026-04-06 20:52 – Updated: 2026-04-07 15:09
VLAI
Title
Mobile Next has Arbitrary Android Intent Execution via mobile_open_url
Summary
Mobile Next is an MCP server for mobile development and automation. Prior to 0.0.50, the mobile_open_url tool in mobile-mcp passes user-supplied URLs directly to Android's intent system without any scheme validation, allowing execution of arbitrary Android intents, including USSD codes, phone calls, SMS messages, and content provider access. This vulnerability is fixed in 0.0.50.
Severity
8.3 (High)
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:H/A:H
CWE
  • CWE-939 - Improper Authorization in Handler for Custom URL Scheme
Assigner
References
Impacted products
Vendor Product Version
mobile-next mobile-mcp Affected: < 0.0.50
Create a notification for this product.
Show details on NVD website
To clipboard 

{
  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "other": {
              "content": {
                "id": "CVE-2026-35394",
                "options": [
                  {
                    "Exploitation": "poc"
                  },
                  {
                    "Automatable": "no"
                  },
                  {
                    "Technical Impact": "partial"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-04-07T14:52:14.299357Z",
                "version": "2.0.3"
              },
              "type": "ssvc"
            }
          }
        ],
        "providerMetadata": {
          "dateUpdated": "2026-04-07T15:09:43.022Z",
          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
        "references": [
          {
            "tags": [
              "exploit"
            ],
            "url": "https://github.com/mobile-next/mobile-mcp/security/advisories/GHSA-5qhv-x9j4-c3vm"
          }
        ],
        "title": "CISA ADP Vulnrichment"
      }
    ],
    "cna": {
      "affected": [
        {
          "product": "mobile-mcp",
          "vendor": "mobile-next",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 0.0.50"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "Mobile Next is an MCP server for mobile development and automation. Prior to 0.0.50, the mobile_open_url tool in mobile-mcp passes user-supplied URLs directly to Android\u0027s intent system without any scheme validation, allowing execution of arbitrary Android intents, including USSD codes, phone calls, SMS messages, and content provider access. This vulnerability is fixed in 0.0.50."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "attackComplexity": "LOW",
            "attackVector": "NETWORK",
            "availabilityImpact": "HIGH",
            "baseScore": 8.3,
            "baseSeverity": "HIGH",
            "confidentialityImpact": "LOW",
            "integrityImpact": "HIGH",
            "privilegesRequired": "NONE",
            "scope": "UNCHANGED",
            "userInteraction": "REQUIRED",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:H/A:H",
            "version": "3.1"
          }
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-939",
              "description": "CWE-939: Improper Authorization in Handler for Custom URL Scheme",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-04-06T20:52:25.170Z",
        "orgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
        "shortName": "GitHub_M"
      },
      "references": [
        {
          "name": "https://github.com/mobile-next/mobile-mcp/security/advisories/GHSA-5qhv-x9j4-c3vm",
          "tags": [
            "x_refsource_CONFIRM"
          ],
          "url": "https://github.com/mobile-next/mobile-mcp/security/advisories/GHSA-5qhv-x9j4-c3vm"
        }
      ],
      "source": {
        "advisory": "GHSA-5qhv-x9j4-c3vm",
        "discovery": "UNKNOWN"
      },
      "title": "Mobile Next has Arbitrary Android Intent Execution via mobile_open_url"
    }
  },
  "cveMetadata": {
    "assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
    "assignerShortName": "GitHub_M",
    "cveId": "CVE-2026-35394",
    "datePublished": "2026-04-06T20:52:25.170Z",
    "dateReserved": "2026-04-02T17:03:42.074Z",
    "dateUpdated": "2026-04-07T15:09:43.022Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}
Mitigation

Phase: Architecture and Design

Description:

  • Utilize a user prompt pop-up to authorize potentially harmful actions such as those modifying data or dealing with sensitive information.
  • When designing functionality of actions in the URL scheme, consider whether the action should be accessible to all mobile applications, or if an allowlist of applications to interface with is appropriate.

No CAPEC attack patterns related to this CWE.

Back to CWE stats page