Vulnerability-Lookup

CVE-2026-34401 (GCVE-0-2026-34401)

Vulnerability from cvelistv5 – Published: 2026-03-31 21:05 – Updated: 2026-04-01 15:53

Title

XML Notepad: XML External Entity (XXE) Injection via Unsafe XmlTextReader in XML Diff and Schema Loading

Summary

XML Notepad is a Windows program that provides a simple intuitive User Interface for browsing and editing XML documents. Prior to version 2.9.0.21, XML Notepad does not disable DTD processing by default which means external entities are resolved automatically. There is a well known attack related to malicious DTD files where an attacker to craft a malicious XML file that loads a DTD that causes XML Notepad to make outbound HTTP/SMB requests, potentially leaking local file contents or capturing the victim's NTLM credentials. This issue has been patched in version 2.9.0.21.

Severity

6.5 (Medium)


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

SSVC

Exploitation: poc Automatable: no Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-04-01 15:45 UTC

CWE

CWE-611 - Improper Restriction of XML External Entity Reference

Assigner

GitHub_M

References

4 references

URL	Tags
https://github.com/microsoft/XmlNotepad/security/…	x_refsource_CONFIRM
https://github.com/microsoft/XmlNotepad/commit/36…	x_refsource_MISC
https://github.com/microsoft/XmlNotepad/commit/c0…	x_refsource_MISC
https://github.com/microsoft/XmlNotepad/releases/…	x_refsource_MISC

Impacted products

1 product

Vendor	Product	Version
microsoft	XmlNotepad	Affected: < 2.9.0.21

Show details on NVD website

JSON

To clipboard

{
  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "other": {
              "content": {
                "id": "CVE-2026-34401",
                "options": [
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                    "Automatable": "no"
                  },
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                  }
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                "role": "CISA Coordinator",
                "timestamp": "2026-04-01T15:45:24.184266Z",
                "version": "2.0.3"
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      }
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        {
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    "redhat_vex": {
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      "product_status:known_not_affected": "1",
      "source": "Red Hat CSAF VEX",
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      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-34401.json",
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FKIE_CVE-2026-34401

Vulnerability from fkie_nvd - Published: 2026-03-31 22:16 - Updated: 2026-06-17 10:39

Severity

6.5 (Medium) - CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N

Summary

References

URL	Tags
security-advisories@github.com	https://github.com/microsoft/XmlNotepad/commit/3665603d61ba10b7827a3724e854748cb780140c	Patch
security-advisories@github.com	https://github.com/microsoft/XmlNotepad/commit/c03ab2311ac6960452eb1ab49098768f851dcc53	Patch
security-advisories@github.com	https://github.com/microsoft/XmlNotepad/releases/tag/2.9.0.21	Product, Release Notes
security-advisories@github.com	https://github.com/microsoft/XmlNotepad/security/advisories/GHSA-5j32-486h-42ch	Mitigation, Vendor Advisory
134c704f-9b21-4f2e-91b3-4a467353bcc0	https://github.com/microsoft/XmlNotepad/security/advisories/GHSA-5j32-486h-42ch	Mitigation, Vendor Advisory

Impacted products

	Vendor	Product	Version
	microsoft	xml_notepad	*

JSON

To clipboard

{
  "affected": [
    {
      "affectedData": [
        {
          "product": "XmlNotepad",
          "vendor": "microsoft",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 2.9.0.21"
            }
          ]
        }
      ],
      "source": "security-advisories@github.com"
    }
  ],
  "configurations": [
    {
      "nodes": [
        {
          "cpeMatch": [
            {
              "criteria": "cpe:2.3:a:microsoft:xml_notepad:*:*:*:*:*:windows:*:*",
              "matchCriteriaId": "F08C7164-A566-4527-8764-F9BC54E164F1",
              "versionEndExcluding": "2.9.0.21",
              "vulnerable": true
            }
          ],
          "negate": false,
          "operator": "OR"
        }
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  ],
  "cveTags": [],
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      "lang": "en",
      "value": "XML Notepad is a Windows program that provides a simple intuitive User Interface for browsing and editing XML documents. Prior to version 2.9.0.21, XML Notepad does not disable DTD processing by default which means external entities are resolved automatically. There is a well known attack related to malicious DTD files where an attacker to craft a malicious XML file that loads a DTD that causes XML Notepad to make outbound HTTP/SMB requests, potentially leaking local file contents or capturing the victim\u0027s NTLM credentials. This issue has been patched in version 2.9.0.21."
    }
  ],
  "id": "CVE-2026-34401",
  "lastModified": "2026-06-17T10:39:00.970",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "LOW",
          "attackVector": "NETWORK",
          "availabilityImpact": "NONE",
          "baseScore": 6.5,
          "baseSeverity": "MEDIUM",
          "confidentialityImpact": "HIGH",
          "integrityImpact": "NONE",
          "privilegesRequired": "NONE",
          "scope": "UNCHANGED",
          "userInteraction": "REQUIRED",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N",
          "version": "3.1"
        },
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        "impactScore": 3.6,
        "source": "security-advisories@github.com",
        "type": "Secondary"
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    "ssvcV203": [
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            },
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  "references": [
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      "tags": [
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        "Vendor Advisory"
      ],
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    },
    {
      "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
      "tags": [
        "Mitigation",
        "Vendor Advisory"
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      "url": "https://github.com/microsoft/XmlNotepad/security/advisories/GHSA-5j32-486h-42ch"
    }
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  "sourceIdentifier": "security-advisories@github.com",
  "vulnStatus": "Analyzed",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-611"
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      ],
      "source": "security-advisories@github.com",
      "type": "Secondary"
    }
  ]
}

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.

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.

Action not permitted

CVE-2026-34401 (GCVE-0-2026-34401)

FKIE_CVE-2026-34401

Tags

Sightings

Nomenclature