Linux Kernel up to 7.2.3 smb is_valid_oplock_break total_read/pdu_size buffer overflow

Summaryinfo

A vulnerability categorized as very critical has been discovered in Linux Kernel up to 7.2.3. Affected by this issue is the function is_valid_oplock_break of the component smb. The manipulation of the argument total_read/pdu_size results in buffer overflow. This vulnerability is reported as CVE-2026-89630. The attack can be launched remotely. No exploit exists. It is advisable to upgrade the affected component.

Detailsinfo

A vulnerability, which was classified as very critical, was found in Linux Kernel up to 7.2.3. Affected is the function is_valid_oplock_break of the component smb. The manipulation of the argument total_read/pdu_size with an unknown input leads to a buffer overflow vulnerability. CWE is classifying the issue as CWE-120. The product copies an input buffer to an output buffer without verifying that the size of the input buffer is less than the size of the output buffer, leading to a buffer overflow. This is going to have an impact on confidentiality, integrity, and availability. CVE summarizes:

In the Linux kernel, the following vulnerability has been resolved: smb: client: restore the data_offset bound in is_valid_oplock_break() Commit 83bfbd0bb902 ("cifs: Remove the RFC1002 header from smb_hdr") changed the quantity this bound is measured against. It used to be srv->total_read minus the 4-byte RFC1002 preamble that total_read then included, so it was the SMB message length. The same commit stopped counting the preamble, and the mechanical substitution to srv->total_read - srv->pdu_size left an expression that is identically zero: standard_receive3() reads MID_HEADER_SIZE() bytes and then exactly pdu_length - MID_HEADER_SIZE() more, adding both to total_read. len is therefore 0, the subtraction below it wraps, and no __u32 DataOffset can exceed the result, so the check from commit 097f5863b1a0 ("cifs: read overflow in is_valid_oplock_break()") no longer rejects anything. Use total_read, which is now the message length on its own.

The advisory is available at git.kernel.org. This vulnerability is traded as CVE-2026-89630 since 09/11/2026. The exploitability is told to be easy. It is possible to launch the attack remotely. Technical details are known, but there is no available exploit. The structure of the vulnerability defines a possible price range of USD $5k-$25k at the moment (estimation calculated on 09/12/2026).

Upgrading to version 7.2.4 or 7.3-rc1 eliminates this vulnerability. Applying the patch 5b16a1967a01ad4496a7206a87c3eb16f1df2b05/ba22f575de9deeae4ae0859ca4315a7698226237 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

License

• open-source

Website

• Vendor: https://www.kernel.org/

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