CVE-2023-32250 Overview
CVE-2023-32250 is a race condition vulnerability in the Linux kernel's ksmbd component, a high-performance in-kernel Server Message Block (SMB) server. The flaw exists in the processing of SMB2_SESSION_SETUP commands and stems from missing locking when operations are performed on a shared object [CWE-362]. A remote, unauthenticated attacker can exploit this race to execute arbitrary code in the context of the Linux kernel.
Critical Impact
Successful exploitation grants kernel-level code execution from the network, fully compromising confidentiality, integrity, and availability of affected hosts.
Affected Products
- Linux kernel versions implementing the ksmbd in-kernel SMB server
- NetApp HCI and HCI Storage Nodes
- NetApp H300S, H410S, H500S, and H700S hybrid storage systems
Discovery Timeline
- 2023-07-10 - CVE-2023-32250 published to the National Vulnerability Database (NVD)
- 2023-08-24 - NetApp publishes advisory NTAP-20230824-0004
- 2024-11-21 - Last updated in NVD database
Technical Details for CVE-2023-32250
Vulnerability Analysis
The vulnerability resides in ksmbd, the kernel-mode SMB3 server introduced in recent Linux kernel releases. When ksmbd processes an SMB2_SESSION_SETUP request, it manipulates session-related objects without holding the appropriate lock. Concurrent SMB2 session setup requests can therefore reach the same object simultaneously, producing inconsistent state during the authentication handshake.
Because ksmbd executes inside the kernel, any memory corruption or use-after-free triggered through this race translates directly into kernel-context primitives. The attack complexity is elevated because the attacker must reliably win the race between competing requests, which explains the elevated complexity rating despite the network attack surface.
The issue is classified under [CWE-362] (Concurrent Execution using Shared Resource with Improper Synchronization). The Zero Day Initiative tracked this finding as advisory ZDI-23-698.
Root Cause
The root cause is the absence of proper mutex or spinlock protection around shared session objects manipulated during SMB2_SESSION_SETUP processing. When two threads service overlapping session setup commands targeting the same object, one thread can free or modify state that the other still references, creating a window for memory corruption.
Attack Vector
Exploitation requires network reachability to a host with ksmbd enabled and listening on TCP port 445. No authentication or user interaction is required, as the race occurs in the session setup path that precedes credential validation. An attacker sends concurrent crafted SMB2_SESSION_SETUP requests to trigger the race and corrupt kernel memory, ultimately pivoting to arbitrary kernel code execution.
No public proof-of-concept code or exploit modules have been published. Refer to the Zero Day Initiative Advisory ZDI-23-698 for additional technical context.
Detection Methods for CVE-2023-32250
Indicators of Compromise
- Unexpected ksmbd worker thread crashes, kernel oops messages, or BUG: entries in dmesg referencing session setup paths.
- Anomalous bursts of concurrent SMB2 SESSION_SETUP requests from a single remote source to TCP port 445.
- Unexplained kernel panics or reboots on Linux hosts exposing ksmbd to untrusted networks.
Detection Strategies
- Monitor kernel logs for crashes, list corruption warnings, or KASAN reports involving ksmbd_session, smb2_sess_setup, or related symbols.
- Inspect SMB traffic for unusually high rates of session setup attempts from the same client, particularly without successful authentication completion.
- Track running kernel versions against vendor-supplied fixed versions to identify hosts still exposed to the flaw.
Monitoring Recommendations
- Alert on any process or service binding to port 445 on systems where SMB serving is not an approved function.
- Forward kernel ring buffer and auditd records to a centralized log platform for correlation across hosts.
- Continuously validate that ksmbd modules are unloaded on systems that do not require an SMB server role.
How to Mitigate CVE-2023-32250
Immediate Actions Required
- Apply the patched Linux kernel from your distribution vendor; consult the Red Hat CVE-2023-32250 Advisory for Red Hat-based systems.
- For NetApp systems, apply updates per NetApp Security Advisory NTAP-20230824-0004.
- Restrict inbound TCP/445 access to trusted management networks using host and perimeter firewalls.
- Disable ksmbd on any host that does not require an in-kernel SMB server.
Patch Information
Upstream Linux maintainers committed fixes to the ksmbd session setup path that introduce proper locking around the affected object operations. Distribution-specific backports are available from Red Hat, NetApp, and other Linux vendors; consult the Red Hat Bugzilla Report #2208849 for build references and fixed package versions.
Workarounds
- Unload the ksmbd kernel module with modprobe -r ksmbd and blacklist it where SMB serving is not needed.
- Use Samba's userspace smbd instead of ksmbd until the kernel patch is applied, reducing exposure to in-kernel SMB parsing flaws.
- Block TCP/445 ingress at the network edge and limit SMB exposure to VPN or management segments only.
# Configuration example: disable and blacklist the ksmbd module
sudo systemctl stop ksmbd.service 2>/dev/null || true
sudo modprobe -r ksmbd
echo 'blacklist ksmbd' | sudo tee /etc/modprobe.d/disable-ksmbd.conf
# Restrict SMB exposure with nftables (example)
sudo nft add rule inet filter input tcp dport 445 drop
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
