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

Severity: critical (CVSS 9.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.8% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-05-06 · updated 2026-10-30
Weakness: CWE-674

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)

Affected products

Linux kernel: from 5.15 before 6.18.16; from 6.19 before 6.19.6; 7.0-rc1 — fixed in 6.18.16, 6.19.6
Linux: 5.15 — fixed in 7.0

How to fix

Upgrade to a fixed version: Linux kernel 6.18.16, 6.19.6; Linux 7.0. Check the vendor advisory for mitigations.

References

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