ksmbd: fix signededness bug in smb_direct_prepare_negotiation()_CVE-2026-43185

9.8 / 10

CRITICAL

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Description

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)

AI Analysis

Heap buffer overflow vulnerability in ksmbd due to a signedness bug in smb_direct_prepare_negotiation()

Basic Information

ID CVE-2026-43185

Source Linux

Published May 6, 2026 at 11:27

Modified May 8, 2026 at 12:41

Affected Product

Vendor Linux

Product Linux

Version 0626e6641f6b467447c81dd7678a69c66f7746cf

Affected Versions Linux Linux 0626e6641f6b467447c81dd7678a69c66f7746cf
Linux Linux 0626e6641f6b467447c81dd7678a69c66f7746cf
Linux Linux 0626e6641f6b467447c81dd7678a69c66f7746cf
Linux Linux 5.15

AI Assessment

AI Score 9.8 / 10

AI Severity Critical

Vendor Linux

Product ksmbd

Version 5.15, 0626e6641f6b467447c81dd7678a69c66f7746cf

References

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    "lastseen": "",
    "description": "In the Linux kernel, the following vulnerability has been resolved:\n\nksmbd: fix signededness bug in smb_direct_prepare_negotiation()\n\nsmb_direct_prepare_negotiation() casts an unsigned __u32 value\nfrom sp->max_recv_size and req->preferred_send_size to a signed\nint before computing min_t(int, ...). A maliciously provided\npreferred_send_size of 0x80000000 will return as smaller than\nmax_recv_size, and then be used to set the maximum allowed\nalowed receive size for the next message.\n\nBy sending a second message with a large value (>1420 bytes)\nthe attacker can then achieve a heap buffer overflow.\n\nThis fix replaces min_t(int, ...) with min_t(u32)",
    "published": "2026-05-06T11:27:56.386Z",
    "modified": "2026-05-08T12:41:03.371Z",
    "type": "cve",
    "title": "ksmbd: fix signededness bug in smb_direct_prepare_negotiation()",
    "source": "Linux",
    "references": "https://git.kernel.org/stable/c/ceae058eb707ddd0d68f0872f9d9f23b7c30c37b\nhttps://git.kernel.org/stable/c/55abc475d096da4a5356b6efb0cfdc6156bc1550\nhttps://git.kernel.org/stable/c/6b4f875aac344cdd52a1f34cc70ed2f874a65757",
    "id": "CVE-2026-43185",
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