CVE-2026-97563
UnknownSummary
In the Linux kernel, the CIFSSMBRead() function (SMB1 client) did not validate the DataOffset field in the server response. A malicious or compromised SMB1 server can return a large DataOffset with a valid DataLength, causing an out-of-bounds read past the response buffer — leaking kernel heap memory (information disclosure) or triggering an oops (denial of service). The vulnerability only affects mounts explicitly using vers=1.0, as SMB1 is not negotiated by default.
Risk Assessment
An attacker controlling an SMB1 server can disclose kernel memory contents (information disclosure) or crash the system (denial of service). The risk applies only to systems that explicitly mount SMB1 shares (vers=1.0).
Recommendation
Update the Linux kernel to a version containing the fix that validates the DataOffset + DataLength range. If possible, stop using SMB1 mounts (vers=1.0) and migrate to SMB2/SMB3.
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Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: smb: client: reject out-of-bounds DataOffset in CIFSSMBRead() The SMB1 synchronous read helper CIFSSMBRead() validates the server's DataLength against CIFSMaxBufSize and the caller's count, but never validates DataOffset. The copy source is formed as &pSMBr->hdr.Protocol + le16_to_cpu(pSMBr->DataOffset) and memcpy()'d for DataLength bytes with no check that the [DataOffset, DataOffset + DataLength) range lies within the response actually received from the server. A malicious or compromised SMB1 server can return a response carrying an in-range DataLength and a large DataOffset, driving the source pointer past the end of the response buffer. The memcpy() then copies adjacent kernel heap into the caller's read buffer (information disclosure), or reads unmapped memory and oopses (denial of service). SMB1 is not negotiated by default; reaching this code requires an explicit vers=1.0 mount. Both DataOffset and the received response length recorded in rsp_iov.iov_len are relative to the start of the SMB header, so reject the response unless DataOffset + DataLength fits within that length, using overflow-safe arithmetic, before forming the source pointer. The response length has been validated by the previous patch, so the DataOffset and DataLength fields can be read safely here. While here, make data_length unsigned. It holds a length derived from unsigned on-the-wire fields and is only ever compared against unsigned quantities; print it with %u accordingly, and add __func__ to the cifs_dbg() calls in this function.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS