Bug 2467196 (CVE-2026-43185)

Summary: CVE-2026-43185 kernel: ksmbd: fix signededness bug in smb_direct_prepare_negotiation()
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
Status: NEW --- QA Contact:
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Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in ksmbd within the Linux kernel. A remote attacker can exploit a signedness bug in the smb_direct_prepare_negotiation() function by sending a specially crafted preferred_send_size value during SMB direct negotiation. This manipulation leads to an incorrect size calculation, allowing a subsequent large message to trigger a heap buffer overflow. A successful exploit could result in arbitrary code execution or a denial of service.
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Description OSIDB Bzimport 2026-05-06 13:10:14 UTC 
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)
Comment 1 Keith Grant 2026-05-06 20:28:37 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026050640-CVE-2026-43185-55a5@gregkh/T