CVE-2023-32269: Linux Kernel Use-After-Free Vulnerability

CVE-2023-32269 Overview

CVE-2023-32269 is a Use-After-Free vulnerability discovered in the Linux kernel's NET/ROM amateur radio protocol implementation. The flaw exists in net/netrom/af_netrom.c where accept() is incorrectly allowed on an already successfully connected AF_NETROM socket, leading to a use-after-free condition that could allow an attacker with local access and elevated privileges to impact system confidentiality, integrity, and availability.

Critical Impact

Local attackers with CAP_NET_ADMIN capability or access to systems with netrom routing configured can exploit this use-after-free vulnerability to potentially execute arbitrary code or cause system instability.

Affected Products

• Linux Kernel versions prior to 6.1.11
• Systems with NET/ROM (netrom) routing configured
• Systems where users have CAP_NET_ADMIN capability

Discovery Timeline

• 2023-05-05 - CVE-2023-32269 published to NVD
• 2025-05-05 - Last updated in NVD database

Technical Details for CVE-2023-32269

Vulnerability Analysis

This vulnerability is classified as CWE-416 (Use After Free), a memory corruption issue that occurs when a program continues to use a pointer after the memory it references has been freed. In the context of CVE-2023-32269, the flaw resides in the NET/ROM protocol handler within the Linux kernel's networking subsystem.

The vulnerability allows the accept() system call to be invoked on an AF_NETROM socket that has already been successfully connected. Under normal operation, accept() should only be valid on listening sockets. When called on a connected socket, the kernel may reference memory structures that are in an inconsistent state, leading to a use-after-free condition.

Exploitation requires either the CAP_NET_ADMIN capability (typically held by root or privileged containers) or a system where netrom routing has been explicitly configured. This limits the attack surface but still presents significant risk in environments where amateur radio networking protocols are in use or where container escapes are a concern.

Root Cause

The root cause is improper state validation in the nr_listen() function within net/netrom/af_netrom.c. The code failed to check whether the socket was already in a connected state before allowing it to transition to a listening state. This oversight allowed the accept() call to proceed on sockets where it should have been rejected, resulting in memory being accessed after it had been freed or reallocated for other purposes.

Attack Vector

The attack vector is local, requiring an attacker to have:

1. Local access to the vulnerable system
2. Either the CAP_NET_ADMIN capability OR access to a system with netrom routing already configured
3. The ability to create and manipulate AF_NETROM sockets

An attacker would create an AF_NETROM socket, establish a connection, then call accept() on the connected socket to trigger the use-after-free condition. This could lead to arbitrary code execution in kernel context, privilege escalation, or denial of service.

 	struct sock *sk = sock->sk;
 
 	lock_sock(sk);
+	if (sock->state != SS_UNCONNECTED) {
+		release_sock(sk);
+		return -EINVAL;
+	}
+
 	if (sk->sk_state != TCP_LISTEN) {
 		memset(&nr_sk(sk)->user_addr, 0, AX25_ADDR_LEN);
 		sk->sk_max_ack_backlog = backlog;

Source: GitHub Linux Commit Update

Detection Methods for CVE-2023-32269

Indicators of Compromise

• Unusual activity involving AF_NETROM socket operations on systems without legitimate amateur radio networking requirements
• Kernel oops or panic messages referencing net/netrom/af_netrom.c or related NET/ROM functions
• Processes with CAP_NET_ADMIN capability making unexpected socket system calls

Detection Strategies

• Monitor for processes attempting to load the netrom kernel module on systems where it is not required
• Implement system call monitoring to detect unusual patterns of socket(), connect(), and accept() calls on AF_NETROM sockets
• Deploy kernel-level monitoring to detect use-after-free exploitation attempts targeting networking subsystems

Monitoring Recommendations

• Enable kernel auditing for socket operations involving the AF_NETROM address family
• Configure SentinelOne agents to monitor for kernel memory corruption indicators
• Review system logs for kernel warnings related to NET/ROM protocol handling
• Monitor for unauthorized loading of amateur radio networking modules

How to Mitigate CVE-2023-32269

Immediate Actions Required

• Update Linux kernel to version 6.1.11 or later which contains the fix
• If patching is not immediately possible, disable the netrom kernel module using modprobe -r netrom and blacklist it
• Review and restrict CAP_NET_ADMIN capability assignments to only essential processes
• Audit systems for unauthorized netrom routing configurations

Patch Information

The vulnerability has been addressed in Linux kernel version 6.1.11 and later releases. The fix adds a state check at the beginning of the nr_listen() function to ensure the socket is in an unconnected state before allowing it to transition to listening mode. If the socket is already connected, the function now returns -EINVAL instead of proceeding.

For detailed patch information, refer to the Linux Kernel ChangeLog 6.1.11 and the kernel commit 6117929209.

Workarounds

• Blacklist the netrom module by adding blacklist netrom to /etc/modprobe.d/blacklist.conf if NET/ROM functionality is not required
• Remove CAP_NET_ADMIN capability from non-essential processes and containers
• Use seccomp filters to restrict access to AF_NETROM socket operations

# Blacklist the netrom module to prevent loading
echo "blacklist netrom" | sudo tee /etc/modprobe.d/netrom-blacklist.conf

# Unload the module if currently loaded
sudo modprobe -r netrom

# Verify the module is not loaded
lsmod | grep netrom