CVE-2026-31708
Received Received - Intake
Out-of-Bounds Read in Linux Kernel SMB Client

Publication date: 2026-05-01

Last updated on: 2026-06-01

Assigner: kernel.org

Description
In the Linux kernel, the following vulnerability has been resolved: smb: client: fix OOB read in smb2_ioctl_query_info QUERY_INFO path smb2_ioctl_query_info() has two response-copy branches: PASSTHRU_FSCTL and the default QUERY_INFO path. The QUERY_INFO branch clamps qi.input_buffer_length to the server-reported OutputBufferLength and then copies qi.input_buffer_length bytes from qi_rsp->Buffer to userspace, but it never verifies that the flexible-array payload actually fits within rsp_iov[1].iov_len. A malicious server can return OutputBufferLength larger than the actual QUERY_INFO response, causing copy_to_user() to walk past the response buffer and expose adjacent kernel heap to userspace. Guard the QUERY_INFO copy with a bounds check on the actual Buffer payload. Use struct_size(qi_rsp, Buffer, qi.input_buffer_length) rather than an open-coded addition so the guard cannot overflow on 32-bit builds.
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Meta Information
Published
2026-05-01
Last Modified
2026-06-01
Generated
2026-06-16
AI Q&A
2026-05-01
EPSS Evaluated
2026-06-15
NVD
CVE-2026-31708
EUVD
EUVD-2026-26517
Affected Vendors & Products
Showing 4 associated CPEs
Vendor Product Version / Range
linux linux_kernel From 6.7 (inc) to 6.12.84 (exc)
linux linux_kernel From 6.13 (inc) to 6.18.25 (exc)
linux linux_kernel From 6.19 (inc) to 7.0.2 (exc)
linux linux_kernel From 5.1 (inc) to 6.6.136 (exc)
Helpful Resources
Exploitability
CWE
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KEV
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CWE ID Description
CWE-125 The product reads data past the end, or before the beginning, of the intended buffer.
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Impact Analysis

This vulnerability can lead to information disclosure by allowing a malicious SMB server to cause the Linux kernel to leak adjacent kernel heap memory to userspace. This could expose sensitive kernel data or other information that should remain protected.

Such exposure could be leveraged by attackers to gain insights into kernel memory layout or other sensitive information, potentially aiding further attacks or privilege escalation.

Executive Summary

This vulnerability exists in the Linux kernel's SMB client, specifically in the smb2_ioctl_query_info function. The function has two response-copy branches, and in the QUERY_INFO path, it copies data from the server response to userspace without properly verifying that the data fits within the expected buffer size.

A malicious SMB server can exploit this by returning a larger OutputBufferLength than the actual response size, causing the kernel to read beyond the intended buffer (an out-of-bounds read). This results in exposing adjacent kernel heap memory to userspace, potentially leaking sensitive kernel data.

The fix involves adding a proper bounds check on the actual buffer payload to prevent this out-of-bounds read, ensuring the copy operation does not exceed the real buffer size.

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