CVE-2023-53246 – A NULL pointer dereference vulnerability in the... (How to Fix)

Q: What is the severity of CVE-2023-53246?

CVE-2023-53246 has a CVSS score of 5.5 (MEDIUM). A NULL pointer dereference vulnerability in the Linux kernel's CIFS filesystem driver causes kernel oops (system crash) when traversing DFS referral links with CONFIG_CIFS_DFS_UPCALL disabled. This affects Linux systems using CIFS/SMB mounts with DFS referrals. The vulnerability leads to denial of service but not privilege escalation.

📋 TL;DR

A NULL pointer dereference vulnerability in the Linux kernel's CIFS filesystem driver causes kernel oops (system crash) when traversing DFS referral links with CONFIG_CIFS_DFS_UPCALL disabled. This affects Linux systems using CIFS/SMB mounts with DFS referrals. The vulnerability leads to denial of service but not privilege escalation.

💻 Affected Systems

Products:

Linux kernel

Versions: Specific affected versions not specified in CVE, but fix commits target stable kernel branches

Operating Systems: Linux distributions using vulnerable kernel versions with CIFS support

Default Config Vulnerable: ✅ No

Notes: Only vulnerable when compiled with CONFIG_CIFS_DFS_UPCALL disabled and using CIFS mounts with DFS referrals.

📦 What is this software?

Linux Kernel by Linux

The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...

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Linux Kernel by Linux

The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...

Learn more about Linux Kernel →

Linux Kernel by Linux

The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...

Learn more about Linux Kernel →

Linux Kernel by Linux

The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...

Learn more about Linux Kernel →

Linux Kernel by Linux

The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...

Learn more about Linux Kernel →

Linux Kernel by Linux

The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...

Learn more about Linux Kernel →

Linux Kernel by Linux

The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...

Learn more about Linux Kernel →

Linux Kernel by Linux

The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...

Learn more about Linux Kernel →

Linux Kernel by Linux

The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...

Learn more about Linux Kernel →

Linux Kernel by Linux

The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...

Learn more about Linux Kernel →

Linux Kernel by Linux

The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...

Learn more about Linux Kernel →

⚠️ Risk & Real-World Impact

🔴

Worst Case

System crash (kernel panic) leading to denial of service for all processes on the affected system, requiring reboot.

🟠

Likely Case

System crash when accessing DFS referral paths via CIFS mounts, causing temporary service disruption until system reboot.

🟢

If Mitigated

No impact if DFS referrals are not used or CONFIG_CIFS_DFS_UPCALL is enabled.

🌐 Internet-Facing: LOW - Requires CIFS mount access and DFS traversal, typically not internet-facing.

🏢 Internal Only: MEDIUM - Internal users with CIFS mount access could trigger crashes affecting shared systems.

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: UNKNOWN

Unauthenticated Exploit: ✅ No

Complexity: MEDIUM

Requires access to CIFS mount and ability to traverse DFS referral paths. Not remote exploitation.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Kernel versions with fix commits: 179a88a8558bbf42991d361595281f3e45d7edfc and related

Vendor Advisory: https://git.kernel.org/stable/c/179a88a8558bbf42991d361595281f3e45d7edfc

Restart Required: Yes

Instructions:

1. Update Linux kernel to version containing fix commits. 2. Rebuild kernel if using custom build. 3. Reboot system to load new kernel.

🔧 Temporary Workarounds

Enable CONFIG_CIFS_DFS_UPCALL

all

Compile kernel with CONFIG_CIFS_DFS_UPCALL=y to avoid NULL pointer dereference

Rebuild kernel with CONFIG_CIFS_DFS_UPCALL enabled in configuration

Avoid DFS referrals

all

Do not use DFS referral paths with CIFS mounts

🧯 If You Can't Patch

Disable CIFS mounts or restrict access to prevent DFS traversal
Monitor for kernel oops/crash events related to CIFS operations

🔍 How to Verify

Check if Vulnerable:

Check kernel configuration for CONFIG_CIFS_DFS_UPCALL setting and kernel version against fix commits

Check Version:

uname -r && grep CONFIG_CIFS_DFS_UPCALL /boot/config-$(uname -r)

Verify Fix Applied:

Verify kernel version includes fix commits and CONFIG_CIFS_DFS_UPCALL is properly handled

📡 Detection & Monitoring

Log Indicators:

Kernel oops messages in dmesg or /var/log/kern.log
NULL pointer dereference errors with cifs_dfs_d_automount

Network Indicators:

CIFS/SMB traffic to DFS referral paths

SIEM Query:

Search for 'kernel: BUG:' or 'kernel: Oops:' with 'cifs' or 'DFS' in system logs

📊 Metadata

CVE ID: CVE-2023-53246

CVSS v3 Score: 5.5 (MEDIUM)

CVSS Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

CWE: CWE-476

EPSS Score: 0.01% exploit probability (1.7th percentile)

Published: September 15, 2025

Last Updated: January 5, 2026

🔗 References

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