CVE-2015-0240

What it actually does

The flaw triggers a free on an uninitialized stack pointer inside the Netlogon ServerPasswordSet RPC handler in smbd, resulting in memory corruption that permits remote arbitrary code execution.

Why it matters to the business

Successful exploitation grants attackers full control of Samba-based file, print, and authentication servers, enabling domain-wide compromise, data theft, or ransomware deployment in environments still running the affected versions.

How an attack unfolds

An attacker sends specially crafted Netlogon packets that reach the _netr_ServerPasswordSet function; the resulting use of an uninitialized pointer causes memory corruption that is turned into remote code execution without authentication.

How to fix it

Upgrade to Samba 3.6.25, 4.0.25, 4.1.17, or 4.2.0rc5 (or newer releases in each respective branch) and restart smbd services.

How to confirm the fix worked

Confirm the running Samba version is no longer in the vulnerable ranges listed in the advisory and perform regression testing with known proof-of-concept Netlogon packets to verify the pointer-handling defect is resolved.

Typical attack path

1. Locate publicly reachable Samba servers exposing the Netlogon service
2. Send crafted ServerPasswordSet RPC packets to trigger the uninitialized pointer free
3. Leverage memory corruption to inject and execute shellcode
4. Establish persistence or move laterally within the domain

How to detect it

Inspect smbd process crash dumps and logs for references to srv_netlog_nt.c or _netr_ServerPasswordSet around the time of unexpected Netlogon connections; correlate with network captures showing unusual RPC traffic on port 445.

What your security team should do

• Prioritize patching all exposed Samba instances to the fixed versions
• Restrict Netlogon RPC access to trusted networks only
• Enable enhanced logging on smbd for Netlogon traffic
• Hunt for post-exploitation artifacts on any systems that were reachable before patching