CVE-2026-98169 in Linux
Summary
by MITRE • 10/06/2026
In the Linux kernel, the following vulnerability has been resolved:
smb: client: fix potential OOB read in smb3_enum_snapshots()
If snapshot_array_size is smaller than GMT_TOKEN_SIZE, smb3_enum_snapshots() sets ret_data_len to sizeof(struct smb_snapshot_array) without verifying the actual length of the server's reply.
Because SMB2_ioctl() places no lower bound on the server-supplied OutputCount and allocates retbuf to exactly that length, a short reply results in ret_data_len exceeding the size of retbuf. The subsequent copy_to_user() then reads past the end of retbuf, leaking adjacent slab memory to userspace. The subsequent clamp check is ineffective as it only reduces ret_data_len.
Fix this by rejecting replies shorter than sizeof(struct smb_snapshot_array) with -EIO. Note that the bound is set to the 12-byte struct size rather than the 16-byte MIN_SNAPSHOT_ARRAY_SIZE defined in MS-SMB2 3.3.5.15.1, because 12 bytes is exactly what copy_to_user() attempts to read.
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Analysis
by VulDB Data Team • 10/07/2026
The vulnerability identified as a potential out-of-bounds (OOB) read within the Linux kernel's SMB client implementation resides specifically in the smb3_enum_snapshots function. This flaw arises from an insufficient validation of server-supplied data lengths during the processing of snapshot enumeration requests. The core issue is triggered when the size of the incoming snapshot array provided by the remote server, referred to as snapshot_array_size, is smaller than a predefined constant known as GMT_TOKEN_SIZE. In such scenarios, the function incorrectly assigns ret_data_len to sizeof(struct smb_snapshot_array) without first verifying that the actual length of the server's reply meets or exceeds this expected size. This logical error creates a discrepancy between the amount of data the code intends to process and the actual memory buffer allocated for receiving it.
The operational mechanics of this vulnerability are closely tied to how the SMB2_ioctl function handles output buffers. The SMB2_ioctl implementation allocates a return buffer, retbuf, with an exact size corresponding only to the OutputCount field supplied by the server in its response packet. It does not enforce any lower bound on this value based on protocol requirements or expected payload sizes. Consequently, if the server returns a short reply where the OutputCount is less than what is required for a valid snapshot array structure, retbuf becomes smaller than the size of struct smb_snapshot_array. Because the earlier logic in smb3_enum_snapshots sets ret_data_len to this larger structural size regardless of the actual buffer capacity, a critical mismatch occurs where ret_data_len exceeds the allocated size of retbuf.
This discrepancy leads directly to an out-of-bounds read condition when the system attempts to copy data from kernel space to user space. The subsequent call to copy_to_user utilizes the inflated ret_data_len value as its length parameter. Since this value is larger than the actual allocation in retbuf, the memory access operation reads past the end of the allocated buffer into adjacent slab memory regions. This results in a information leak vulnerability where sensitive kernel memory contents are exposed to userspace applications interacting with the SMB client interface. The existing clamp check designed to limit data length proves ineffective in this context because it only serves to reduce ret_data_len but does not validate that the value is within safe bounds relative to the buffer size, allowing the oversized read operation to proceed unchecked.
From a security classification perspective, this vulnerability aligns with CWE-125, which describes out-of-bounds read conditions where software reads data past the end of a buffer or memory region. In terms of adversarial tactics, this flaw facilitates information disclosure and could potentially be leveraged in conjunction with other vulnerabilities to achieve arbitrary code execution if the leaked kernel memory contains pointers or sensitive cryptographic keys. The attack vector is remote, requiring an attacker to control or manipulate the SMB server's response length during a snapshot enumeration request, placing it within the scope of network-based exploitation techniques documented under ATT&CK tactics related to Collection and Exfiltration over Application Layer Protocols.
The resolution for this issue involves implementing strict validation logic before processing the snapshot array data. The fix explicitly rejects any replies that are shorter than sizeof(struct smb_snapshot_array) by returning an I/O error code, specifically -EIO. This ensures that only responses containing sufficient data to safely populate the structure are processed further. Notably, the bound is set strictly to 12 bytes, which corresponds exactly to the size of struct smb_snapshot_array and matches what copy_to_user attempts to read, rather than adhering to the larger MIN_SNAPSHOT_ARRAY_SIZE defined in Microsoft SMB2 specification section 3.3.5.15.1. This precise alignment ensures that memory access remains within allocated boundaries while maintaining compatibility with actual client expectations for minimal valid responses.
To mitigate this vulnerability and similar issues in network-facing kernel components, system administrators should ensure that the Linux kernel is updated to a version containing this patch. For environments where immediate patching is not feasible, deploying intrusion detection systems capable of analyzing SMB protocol traffic may help identify anomalous packet sizes or malformed requests targeting snapshot enumeration endpoints. Additionally, enforcing strict input validation at the application layer for any custom SMB clients can provide an additional defense-in-depth measure against malformed server responses that attempt to exploit buffer length discrepancies in kernel-space handlers.