Linux Kernel up to 6.18.15/6.19.5 smb_direct_prepare_negotiation buffer overflow

Summaryinfo

A vulnerability marked as critical has been reported in Linux Kernel up to 6.18.15/6.19.5. This vulnerability affects the function smb_direct_prepare_negotiation. The manipulation leads to buffer overflow. This vulnerability is listed as CVE-2026-43185. There is no available exploit. It is suggested to upgrade the affected component.

Detailsinfo

A vulnerability was found in Linux Kernel up to 6.18.15/6.19.5 and classified as critical. This issue affects the function smb_direct_prepare_negotiation. The manipulation with an unknown input leads to a buffer overflow vulnerability. Using CWE to declare the problem leads to 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. Impacted is confidentiality, integrity, and availability. The summary by CVE is:

In the Linux kernel, the following vulnerability has been resolved: ksmbd: fix signededness bug in smb_direct_prepare_negotiation() smb_direct_prepare_negotiation() casts an unsigned __u32 value from sp->max_recv_size and req->preferred_send_size to a signed int before computing min_t(int, ...). A maliciously provided preferred_send_size of 0x80000000 will return as smaller than max_recv_size, and then be used to set the maximum allowed alowed receive size for the next message. By sending a second message with a large value (>1420 bytes) the attacker can then achieve a heap buffer overflow. This fix replaces min_t(int, ...) with min_t(u32)

It is possible to read the advisory at git.kernel.org. The identification of this vulnerability is CVE-2026-43185 since 05/01/2026. The exploitation is known to be easy. Technical details of the vulnerability are known, but there is no available exploit. The pricing for an exploit might be around USD $5k-$25k at the moment (estimation calculated on 05/06/2026).

Upgrading to version 6.18.16 or 6.19.6 eliminates this vulnerability. Applying the patch ceae058eb707ddd0d68f0872f9d9f23b7c30c37b/55abc475d096da4a5356b6efb0cfdc6156bc1550/6b4f875aac344cdd52a1f34cc70ed2f874a65757 is able to eliminate this problem. The bugfix is ready for download at git.kernel.org. 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

• 6.18.0
• 6.18.1
• 6.18.2
• 6.18.3
• 6.18.4
• 6.18.5
• 6.18.6
• 6.18.7
• 6.18.8
• 6.18.9
• 6.18.10
• 6.18.11
• 6.18.12
• 6.18.13
• 6.18.14
• 6.18.15
• 6.19.0
• 6.19.1
• 6.19.2
• 6.19.3
• 6.19.4
• 6.19.5

License

• open-source

Website

• Vendor: https://www.kernel.org/

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