Linux Kernel up to 7.2.6/7.3-rc2 SMB Client CIFSSMBRead DataOffset/DataLength out-of-bounds

Summaryinfo

A vulnerability marked as critical has been reported in Linux Kernel up to 7.2.6/7.3-rc2. This issue affects the function CIFSSMBRead of the component SMB Client. This manipulation of the argument DataOffset/DataLength causes out-of-bounds. The identification of this vulnerability is CVE-2026-97563. It is possible to initiate the attack remotely. There is no exploit available. It is suggested to upgrade the affected component.

Detailsinfo

A vulnerability was found in Linux Kernel up to 7.2.6/7.3-rc2. It has been declared as critical. Affected by this vulnerability is the function CIFSSMBRead of the component SMB Client. The manipulation of the argument DataOffset/DataLength with an unknown input leads to a out-of-bounds vulnerability. The CWE definition for the vulnerability is CWE-125. The product reads data past the end, or before the beginning, of the intended buffer. As an impact it is known to affect confidentiality, integrity, and availability. The summary by CVE is:

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.

The advisory is shared at git.kernel.org. This vulnerability is known as CVE-2026-97563 since 09/24/2026. The exploitation appears to be easy. The attack can be launched remotely. It demands that the victim is doing some kind of user interaction. Technical details are known, but no exploit is available. The price for an exploit might be around USD $0-$5k at the moment (estimation calculated on 09/25/2026).

Upgrading to version 7.2.7 or 7.3-rc3 eliminates this vulnerability. Applying the patch 667feba13e78d16393aacb15869f70970f422227/5be5bdda5863eacc964b609ba927764f253431b3 is able to eliminate this problem. The best possible mitigation is suggested to be upgrading to the latest version.

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Productinfo

Type

• Operating System

Vendor

• Linux

Name

• Kernel

Version

• 7.2.0
• 7.2.1
• 7.2.2
• 7.2.3
• 7.2.4
• 7.2.5
• 7.2.6
• 7.3-rc1
• 7.3-rc2

License

• open-source

Website

• Vendor: https://www.kernel.org/

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