CVE-2023-4458

What it actually does

Out-of-bounds read during extended attribute parsing in the ksmbd kernel module allows disclosure of adjacent kernel memory contents.

Why it matters to the business

Attackers may obtain sensitive kernel data from Linux servers that expose SMB shares via ksmbd, increasing risk of further compromise on affected systems.

How an attack unfolds

An attacker with network access to a ksmbd-enabled SMB share crafts a request containing malformed extended attributes that triggers an unchecked read past the allocated buffer, leaking memory contents back to the attacker.

How to fix it

Apply the kernel patch that resolves the issue (commit ffc253263a1375a65fa6c9f62a893e9767fbebfa) or upgrade to a Linux kernel version containing this fix. Disable ksmbd if SMB functionality is not required.

How to confirm the fix worked

Confirm the running kernel contains commit ffc253263a1375a65fa6c9f62a893e9767fbebfa or later; test that crafted extended attribute requests no longer return out-of-bounds data.

Typical attack path

1. Identify Linux hosts exposing ksmbd SMB shares
2. Send specially crafted extended attribute requests to the ksmbd module
3. Trigger the out-of-bounds read to obtain leaked kernel memory
4. Analyze leaked data for credentials, pointers, or other sensitive information

How to detect it

Review ksmbd-related kernel logs and audit records for unusual extended attribute operations or SMB session anomalies; correlate with network traffic to SMB ports from untrusted sources.

What your security team should do

• Disable ksmbd on systems where SMB sharing is unnecessary
• Prioritize patching of internet-facing or high-value Linux servers running ksmbd
• Monitor for new kernel releases containing the referenced fix
• Review SMB exposure and apply least-privilege network access controls