CVE-2023-1652: Linux Kernel Use-After-Free Vulnerability

CVE-2023-1652 Overview

A use-after-free vulnerability has been identified in the Linux Kernel's NFS (Network File System) implementation. The flaw exists in the nfsd4_ssc_setup_dul function within fs/nfsd/nfs4proc.c. This memory corruption issue could allow a local attacker with low privileges to crash the system, resulting in a denial of service condition, or potentially leak sensitive kernel memory information.

Critical Impact

Local attackers can exploit this use-after-free vulnerability to cause system crashes or extract sensitive kernel information, affecting system availability and confidentiality.

Affected Products

• Linux Kernel (multiple versions)
• Linux Kernel 6.2 RC1 through RC4
• Red Hat Enterprise Linux 9.0

Discovery Timeline

• 2023-03-29 - CVE-2023-1652 published to NVD
• 2025-02-18 - Last updated in NVD database

Technical Details for CVE-2023-1652

Vulnerability Analysis

This use-after-free vulnerability (CWE-416) occurs in the NFS server daemon (nfsd) subsystem of the Linux Kernel. Use-after-free flaws arise when a program continues to use memory after it has been freed, leading to undefined behavior. In this case, the vulnerable code path resides in the nfsd4_ssc_setup_dul function responsible for handling NFSv4 server-side copy operations.

When exploited, the vulnerability allows an attacker to reference memory that has already been deallocated. This can result in two primary attack outcomes: system crashes through memory corruption leading to kernel panic, or information disclosure by reading data from reallocated memory regions that may contain sensitive kernel information.

The attack requires local access and low privileges, making it particularly concerning in multi-tenant environments or systems where users have shell access.

Root Cause

The root cause of this vulnerability lies in improper memory lifecycle management within the nfsd4_ssc_setup_dul function. The code fails to properly track object references during NFSv4 server-side copy setup operations. When an object is freed but references to it remain, subsequent operations that attempt to access or manipulate this memory can trigger the use-after-free condition.

The NFS filesystem component does not adequately validate or nullify pointers after memory deallocation, leaving dangling references that can be exploited through carefully crafted local operations.

Attack Vector

The attack vector for CVE-2023-1652 is local, requiring an attacker to have authenticated access to the target system. The exploitation process involves:

1. The attacker gains local access to a system running a vulnerable Linux Kernel version with NFS server functionality enabled
2. Through interaction with the NFS server daemon, the attacker triggers specific operations that invoke the vulnerable nfsd4_ssc_setup_dul function
3. By manipulating the timing or sequence of NFS operations, the attacker can cause the use-after-free condition
4. Depending on the attacker's goal, this results in either a kernel crash (denial of service) or memory information leakage

The vulnerability mechanism involves the NFS server-side copy functionality in NFSv4 where memory objects are freed prematurely while still being referenced by other kernel components. For detailed technical analysis, see the Red Hat CVE-2023-1652 Advisory.

Detection Methods for CVE-2023-1652

Indicators of Compromise

• Unexpected kernel panic or system crash events related to NFS operations
• Kernel oops messages referencing nfsd4_ssc_setup_dul or nfs4proc.c in system logs
• Abnormal NFS server daemon behavior or unexpected terminations
• Memory corruption warnings in kernel ring buffer (dmesg) related to NFSD

Detection Strategies

• Monitor kernel logs for use-after-free warnings and stack traces involving NFS components
• Implement kernel crash dump analysis to identify exploitation attempts
• Deploy SentinelOne Singularity for real-time kernel-level threat detection and behavioral analysis
• Use kernel debugging tools like KASAN (Kernel Address Sanitizer) in test environments to detect memory safety violations

Monitoring Recommendations

• Enable enhanced kernel logging for NFS subsystem operations
• Configure crash dump collection and analysis for post-incident forensics
• Monitor system stability metrics and unexpected NFS service interruptions
• Implement file integrity monitoring for kernel modules related to NFS functionality

How to Mitigate CVE-2023-1652

Immediate Actions Required

• Identify all systems running affected Linux Kernel versions with NFS server functionality
• Apply vendor-provided kernel patches immediately after testing in non-production environments
• Consider temporarily disabling NFSv4 server-side copy functionality if patches cannot be immediately applied
• Restrict local access to systems running NFS services to trusted users only

Patch Information

Red Hat has released security updates to address this vulnerability in Enterprise Linux 9.0. Administrators should consult the Red Hat CVE-2023-1652 Advisory for specific patch information and update instructions.

For systems running upstream Linux Kernel, update to a patched kernel version that includes the fix for nfsd4_ssc_setup_dul. The NetApp Security Advisory NTAP-20230511 also provides relevant guidance for affected NetApp products.

Workarounds

• Disable NFS server functionality if not required for business operations
• Restrict local user access to systems running vulnerable NFS services
• Implement network segmentation to limit exposure of NFS servers
• Enable SELinux or AppArmor policies to constrain NFS daemon capabilities

# Check current kernel version
uname -r

# Verify NFS server status
systemctl status nfs-server

# Temporarily disable NFS server if not required
systemctl stop nfs-server
systemctl disable nfs-server

# Update kernel packages (Red Hat/CentOS/RHEL)
yum update kernel

# Reboot to load patched kernel
reboot