CVE-2024-50086

What it actually does

Race condition between SMB2 session logoff and session setup in ksmbd allows use-after-free on the session structure due to missing locking when marking sessions expired and insufficient reference counting.

Why it matters to the business

Linux servers exposing SMB shares face risk of crashes or potential remote code execution, which can disrupt file services, enable data theft, or lead to full system compromise in environments using the kernel SMB server.

How an attack unfolds

An attacker with network access to an SMB server initiates concurrent session setup and logoff requests; the race allows a freed session object to be accessed, enabling use-after-free exploitation for denial of service or privilege escalation, consistent with patterns seen in broad 2024 zero-day campaigns by espionage and financially motivated actors targeting Linux kernel flaws.

How to fix it

Upgrade the Linux kernel to commit 0f62358ce85b2d4c949ef1b648be01b29cec667a or later; for affected sssd packages on Ubuntu 16.04 LTS update to version 1.13.1-2. Disable ksmbd if SMB server functionality is not required.

How to confirm the fix worked

Verify running kernel contains the referenced commit or updated package version; test concurrent session operations under load to confirm absence of UAF conditions; review kernel build configuration for ksmbd.

Typical attack path

1. Establish network connectivity to target SMB service
2. Issue parallel SMB2 SESSION_SETUP and SESSION_LOGOFF requests
3. Trigger dereference of expired session structure after free
4. Leverage UAF for memory corruption leading to code execution or crash

How to detect it

Examine kernel ring buffer and system logs for ksmbd session expiration messages, use-after-free warnings, or oops traces; correlate with SMB connection attempts from untrusted sources around the time of any crashes.

What your security team should do

• Prioritize kernel updates on all systems exposing SMB shares via ksmbd
• Restrict SMB access to trusted networks and enforce strong authentication
• Monitor kernel logs for session-related warnings or crashes
• Consider disabling ksmbd module where SMB server capability is unnecessary