CVE-2023-3772: Red Hat Enterprise Linux DOS Vulnerability

CVE-2023-3772 Overview

A flaw was found in the Linux kernel's IP framework for transforming packets (XFRM subsystem). This vulnerability allows a malicious user with CAP_NET_ADMIN privileges to directly dereference a NULL pointer in the xfrm_update_ae_params() function, leading to a possible kernel crash and denial of service condition.

Critical Impact

Local attackers with elevated network administration capabilities can crash affected Linux systems, causing service disruption and potential system instability.

Affected Products

• Linux Kernel (all affected versions)
• Red Hat Enterprise Linux 8.0 and 9.0
• Red Hat Enterprise Linux for Real Time 8.0
• Red Hat Enterprise Linux for Real Time for NFV 8.0
• Fedora Linux
• Debian Linux 10.0 and 12.0

Discovery Timeline

• July 25, 2023 - CVE-2023-3772 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2023-3772

Vulnerability Analysis

This vulnerability resides in the XFRM (IPsec Transformation) subsystem of the Linux kernel, which is responsible for implementing IPsec security associations and policies. The flaw is classified as CWE-476 (NULL Pointer Dereference), a memory corruption issue that occurs when the kernel attempts to access memory through a pointer that has not been properly initialized or has been set to NULL.

The vulnerable function xfrm_update_ae_params() fails to validate pointer validity before dereferencing, allowing an attacker with the CAP_NET_ADMIN capability to trigger a NULL pointer dereference. While the attack requires local access and elevated privileges, it can effectively crash the kernel, causing a denial of service condition that affects all services running on the system.

Root Cause

The root cause of this vulnerability is improper NULL pointer validation in the XFRM subsystem's xfrm_update_ae_params() function. When processing security association parameters, the function does not adequately check whether certain pointer values are valid before attempting to dereference them. This missing validation allows a crafted request from a privileged user to trigger a NULL pointer access, causing an immediate kernel panic.

Attack Vector

The attack requires local access to the target system with CAP_NET_ADMIN privileges. An attacker must be able to interact with the XFRM subsystem through netlink sockets or similar kernel interfaces. By sending specially crafted requests to update XFRM security association parameters, the attacker can cause the kernel to attempt to dereference a NULL pointer.

The vulnerability is exploited through the following attack flow:

1. Attacker gains access to a system with CAP_NET_ADMIN capability
2. Attacker sends malformed XFRM configuration requests via netlink
3. The kernel's xfrm_update_ae_params() function processes the request
4. A NULL pointer dereference occurs, causing a kernel panic
5. System becomes unavailable until manually rebooted

Detection Methods for CVE-2023-3772

Indicators of Compromise

• Unexpected kernel panic or system crashes with XFRM-related stack traces
• Kernel oops messages referencing xfrm_update_ae_params or related XFRM functions
• Suspicious netlink socket activity from users with CAP_NET_ADMIN privileges
• Repeated system reboots without clear cause on systems using IPsec

Detection Strategies

• Monitor kernel logs for NULL pointer dereference errors in XFRM subsystem functions
• Implement auditd rules to track netlink socket operations related to XFRM configuration
• Deploy endpoint detection solutions capable of identifying kernel-level anomalies
• Configure crash dump collection to capture kernel panic events for forensic analysis

Monitoring Recommendations

• Enable kernel crash dump mechanisms (kdump) to capture kernel panic states
• Configure syslog to forward kernel messages to a centralized logging system
• Monitor for unusual patterns of system reboots across the infrastructure
• Track user capability assignments, particularly CAP_NET_ADMIN grants

How to Mitigate CVE-2023-3772

Immediate Actions Required

• Apply the latest kernel security patches from your Linux distribution vendor
• Review and restrict CAP_NET_ADMIN capability assignments to trusted users only
• Consider temporarily disabling XFRM/IPsec functionality if not required
• Implement network segmentation to limit potential attacker access to vulnerable systems

Patch Information

Multiple vendors have released security patches addressing this vulnerability:

• Red Hat: Security advisories RHSA-2023:6583, RHSA-2023:6901, RHSA-2023:7077, RHSA-2024:0412, and RHSA-2024:0575
• Debian: Security advisory DSA-5492 and LTS announcements for Debian 10 and 12

For detailed patch information, consult the Red Hat CVE Report or the Red Hat Bugzilla entry 2218943.

Workarounds

• Audit and minimize the number of users and processes with CAP_NET_ADMIN capability
• Implement mandatory access control (SELinux/AppArmor) policies restricting XFRM operations
• Use container isolation to limit kernel subsystem access where applicable
• Deploy runtime security monitoring to detect exploitation attempts

# Check for users with CAP_NET_ADMIN capability
getcap -r / 2>/dev/null | grep cap_net_admin

# Audit XFRM-related netlink operations (add to audit.rules)
-a always,exit -F arch=b64 -S socket -F a0=16 -F a2=15 -k xfrm_netlink

# Verify current kernel version for patch status
uname -r