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Linux KernelOperating system · Linux

CVE-2026-43185

CRITICAL · 9.8 CVSS v3.1 Published 2026-05-06
Fix available
A fix is available. Upgrade to 6.18.16 / 6.19.6 or later.
See remediation →
100/100
Remediation priority · Urgent
Remotely reachable No privileges Zero-click Patch available

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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)

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

This is a signedness bug in Linux kernel's ksmbd SMB server in function smb_direct_prepare_negotiation(). Unsigned __u32 values (sp->max_recv_size and req->preferred_send_size) are incorrectly cast to signed int before min_t() comparison. A malicious preferred_send_size of 0x80000000 wraps to negative as signed int (-2147483648), appearing smaller than max_recv_size and causing an undersized buffer allocation. Attacker sends a second message exceeding 1420 bytes to trigger heap buffer overflow.

MitigationApply the upstream kernel patch replacing min_t(int, ...) with min_t(u32, ...) in smb_direct_prepare_negotiation() to preserve unsigned comparison semantics, then rebuild and deploy the fixed kernel.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Linux KernelOperating system
Affected:>= 5.15, < 6.18.16>= 6.19, < 6.19.6= 7.0

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

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

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Verify ksmbd kernel module is loaded
    Run `lsmod | grep ksmbd` or check `/sys/module/ksmbd/version` if it exists
    Affected if The ksmbd module is loaded and running as a kernel module (not built-in to kernel)
  2. Check kernel version against affected ranges
    Run `uname -r` or `cat /proc/version` to get the kernel version number
    Affected if Kernel version is >= 5.15 and < 6.18.16, OR >= 6.19 and < 6.19.6, OR equals 7.0
  3. Verify SMB server functionality is enabled
    Check if ksmbd is actively serving via `systemctl status ksmbd` or `ps aux | grep ksmbd` or check SMB shares being served
    Affected if The system is running ksmbd as an active SMB server daemon
  4. Check if SMB direct/RDMA is configured
    Examine ksmbd configuration files or running parameters for SMB direct (RDMA) support - look for 'smb_direct' or 'rdma' in config or module parameters
    Affected if SMB direct/RDMA is enabled, as this vulnerability requires the smb_direct_prepare_negotiation() function to be exercised during SMB negotiation

The system is affected if ksmbd is actively running as an SMB server AND the kernel version falls within the affected ranges, particularly when SMB direct (RDMA) support is enabled in the configuration.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 6.18.16 / 6.19.6 or later
Fixed in 6.18.166.19.6
Vendor patch git.kernel.org →
Interim mitigation

Apply the upstream kernel patch replacing min_t(int, ...) with min_t(u32, ...) in smb_direct_prepare_negotiation() to preserve unsigned comparison semantics, then rebuild and deploy the fixed kernel.

Recommended fix High confidence

Upgrade to Linux Kernel 6.18.16 or later, OR 6.19.6 or later (depending on which branch you are on)

  1. Identify the currently running kernel version using `uname -r`
  2. If running a distribution kernel (e.g., Ubuntu, Debian, RHEL), check if a distribution-provided kernel update is available that includes this fix. For enterprise distributions, this may be in a subsequent minor update.
  3. For custom-built kernels: Apply the patch from commit 55abc475d096da4a5356b6efb0cfdc6156bc1550 (https://git.kernel.org/stable/c/55abc475d096da4a5356b6efb0cfdc6156bc1550). The fix changes `min_t(int, ...)` to `min_t(u32, ...)` in the smb_direct_prepare_negotiation() function in the ksmbd module.
  4. Rebuild the kernel with the fix applied
  5. Reboot into the fixed kernel
  6. Verify the fix is applied by checking the smb_direct_prepare_negotiation() function source code for the corrected min_t(u32, ...) usage
Caveat Kernel upgrades may require rebuilding out-of-tree modules. Ensure compatibility with system hardware and other software dependencies before upgrading.

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Linux Kernel Scoped from the published advisory
  • Consultation1.0 h
  • Implementation2.0 h
  • Testing3.0 h
  • Review / QA2.0 h
8.0 hours of engineering $1,370
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-43185 in production — separate from our analysis above.

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What this is

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What belongs here
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  • Version or environment caveats, and links to real fixes
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