GHSA-HR3H-X6GQ-RQCP

Vulnerability from github – Published: 2021-08-25 14:45 – Updated: 2025-04-17 12:45
VLAI?
Summary
Cross site scripting via HTML attributes in the back end
Details

Impact

It is possible for untrusted users to inject malicious code into HTML attributes in the back end, which will be executed both in the element preview (back end) and on the website (front end).

Installations are only affected if there are untrusted back end users who have the rights to modify HTML fields (e.g. TinyMCE).

Patches

Update to Contao 4.4.56, 4.9.18 or 4.11.7

Workarounds

Disable all fields that allow HTML for untrusted back end users or disable the login for these users.

References

https://contao.org/en/security-advisories/cross-site-scripting-via-html-attributes-in-the-back-end

For more information

If you have any questions or comments about this advisory, open an issue in contao/contao.

Credits

Thanks to Mikhail Khramenkov and Moritz Vondano for reporting this security issue.

Severity ?
5.9 (Medium)
CVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:C/C:L/I:L/A:L
Show details on source website
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{
  "affected": [
    {
      "package": {
        "ecosystem": "Packagist",
        "name": "contao/core-bundle"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "4.0.0"
            },
            {
              "fixed": "4.4.56"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "Packagist",
        "name": "contao/contao"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "4.0.0"
            },
            {
              "fixed": "4.4.56"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "Packagist",
        "name": "contao/contao"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "4.5.0"
            },
            {
              "fixed": "4.9.18"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "Packagist",
        "name": "contao/contao"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "4.10.0"
            },
            {
              "fixed": "4.11.7"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "Packagist",
        "name": "contao/core-bundle"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "4.5.0"
            },
            {
              "fixed": "4.9.18"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "Packagist",
        "name": "contao/core-bundle"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "4.10.0"
            },
            {
              "fixed": "4.11.7"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2021-35955"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-79"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2021-08-24T18:55:48Z",
    "nvd_published_at": "2021-08-12T15:15:00Z",
    "severity": "MODERATE"
  },
  "details": "### Impact\n\nIt is possible for untrusted users to inject malicious code into HTML attributes in the back end, which will be executed both in the element preview (back end) and on the website (front end).\n\nInstallations are only affected if there are untrusted back end users who have the rights to modify HTML fields (e.g. TinyMCE).\n\n### Patches\n\nUpdate to Contao 4.4.56, 4.9.18 or 4.11.7\n\n### Workarounds\n\nDisable all fields that allow HTML for untrusted back end users or disable the login for these users.\n\n### References\n\nhttps://contao.org/en/security-advisories/cross-site-scripting-via-html-attributes-in-the-back-end\n\n### For more information\n\nIf you have any questions or comments about this advisory, open an issue in [contao/contao](https://github.com/contao/contao/issues/new/choose).\n\n### Credits\n\nThanks to Mikhail Khramenkov and Moritz Vondano for reporting this security issue.",
  "id": "GHSA-hr3h-x6gq-rqcp",
  "modified": "2025-04-17T12:45:11Z",
  "published": "2021-08-25T14:45:01Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/contao/contao/security/advisories/GHSA-hr3h-x6gq-rqcp"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2021-35955"
    },
    {
      "type": "WEB",
      "url": "https://contao.org/en/news/contao-4-9-16-and-4-11-5-are-available.html"
    },
    {
      "type": "WEB",
      "url": "https://contao.org/en/security-advisories/cross-site-scripting-via-html-attributes-in-the-back-end.html"
    },
    {
      "type": "WEB",
      "url": "https://github.com/FriendsOfPHP/security-advisories/blob/master/contao/contao/CVE-2021-35955.yaml"
    },
    {
      "type": "WEB",
      "url": "https://github.com/FriendsOfPHP/security-advisories/blob/master/contao/core-bundle/CVE-2021-35955.yaml"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/contao/contao"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:C/C:L/I:L/A:L",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Cross site scripting via HTML attributes in the back end"
}


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  • 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.
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  • 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.



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