CVE-2024-26936

What it actually does

Missing size validation of SMB2 request payload and header fields before allocating or accessing the response buffer in ksmbd leads to potential out-of-bounds access on the request buffer.

Why it matters to the business

Linux systems running ksmbd as an SMB server face risk of kernel instability, crashes, or memory corruption that can disrupt file sharing services and require emergency patching across server fleets.

How an attack unfolds

An attacker sends a crafted SMB2 request containing malformed size fields in the header or payload; ksmbd uses these unvalidated values during response buffer allocation, resulting in out-of-bounds operations on the request buffer.

How to fix it

Apply the upstream fix by updating the Linux kernel to the commit 8f3d0bf1d0c62b539d54c5b9108a845cff619b99 or later stable releases containing this change; disable ksmbd if SMB server functionality is not required.

How to confirm the fix worked

Confirm the kernel source contains commit 8f3d0bf1d0c62b539d54c5b9108a845cff619b99 and test that ksmbd rejects oversized or malformed SMB2 requests without performing out-of-bounds operations.

Typical attack path

1. Establish SMB connection to target ksmbd instance
2. Send SMB2 request with invalid buffer size fields
3. Trigger smb2_allocate_rsp_buf() using unvalidated request data
4. Cause out-of-bounds access during buffer handling

How to detect it

Review kernel logs for ksmbd-related oops, panic, or buffer access warnings; inspect SMB traffic for anomalous request sizes preceding crashes.

What your security team should do

• Prioritize kernel updates on all systems exposing ksmbd
• Audit configurations to ensure ksmbd is enabled only where necessary
• Monitor for kernel oops or panic logs related to ksmbd buffer handling
• Plan staged rollout of patched kernels to production SMB servers