CVE-2026-23098: Linux Kernel Use-After-Free Vulnerability

CVE-2026-23098 Overview

CVE-2026-23098 is a double-free vulnerability in the Linux kernel's NET/ROM (Network Radio Operator Mode) subsystem. The flaw exists in the nr_route_frame() function where the old_skb socket buffer is immediately freed without first checking if the nr_neigh->ax25 pointer is NULL. When this pointer is NULL, the caller function will attempt to free old_skb again, resulting in a double-free condition that can lead to memory corruption and potential system instability.

Critical Impact

This double-free vulnerability in the Linux kernel's NET/ROM subsystem can lead to memory corruption, kernel panics, and potential privilege escalation on systems using amateur radio packet networking.

Affected Products

• Linux Kernel (NET/ROM subsystem enabled)
• Systems with AX.25 protocol support
• Amateur radio packet networking configurations

Discovery Timeline

• 2026-02-04 - CVE-2026-23098 published to NVD
• 2026-02-05 - Last updated in NVD database

Technical Details for CVE-2026-23098

Vulnerability Analysis

The vulnerability resides in the NET/ROM routing implementation within the Linux kernel. NET/ROM is a networking protocol used in amateur radio packet networks built on top of the AX.25 protocol. The nr_route_frame() function is responsible for routing frames through the NET/ROM network.

The core issue is a missing NULL pointer check before freeing a socket buffer. When nr_route_frame() is called, it unconditionally frees old_skb regardless of the state of nr_neigh->ax25. If this pointer is NULL, the function's caller also attempts to free the same old_skb, resulting in a double-free condition.

Double-free vulnerabilities can be exploited to corrupt memory allocator metadata, potentially allowing an attacker to achieve arbitrary code execution or privilege escalation within the kernel context.

Root Cause

The root cause is improper memory management in the nr_route_frame() function. The code path that frees old_skb does not include a conditional check to verify that nr_neigh->ax25 is valid before performing the free operation. This oversight creates a scenario where the same memory allocation can be freed twice - once in nr_route_frame() and again in the calling function.

The fix requires adding a NULL check for nr_neigh->ax25 before freeing old_skb, ensuring the buffer is only freed when the AX.25 neighbor connection is properly established.

Attack Vector

The attack vector for this vulnerability requires local access to a system with NET/ROM and AX.25 protocol support enabled. An attacker would need to manipulate network conditions or craft specific packet sequences that cause nr_neigh->ax25 to be NULL when nr_route_frame() is invoked.

The vulnerability is triggered when:

1. A NET/ROM frame routing operation is initiated
2. The neighbor AX.25 connection pointer (nr_neigh->ax25) is NULL
3. The old_skb buffer is freed in nr_route_frame()
4. The caller function subsequently attempts to free the same buffer

This creates a use-after-free condition in the kernel memory allocator that could be leveraged for further exploitation.

Detection Methods for CVE-2026-23098

Indicators of Compromise

• Unexpected kernel panics or oops messages referencing nr_route_frame or NET/ROM subsystem
• Memory corruption warnings in kernel logs related to socket buffer operations
• System instability on hosts with AX.25/NET/ROM networking configured
• SLUB allocator double-free detection messages in dmesg output

Detection Strategies

• Monitor kernel logs for double-free warnings or memory corruption alerts involving NET/ROM components
• Implement kernel memory debugging with KASAN (Kernel Address Sanitizer) to detect memory errors
• Review system logs for crashes originating from net/netrom/nr_route.c
• Deploy SentinelOne Singularity Platform for real-time kernel anomaly detection

Monitoring Recommendations

• Enable kernel memory debugging features in test environments to identify exploitation attempts
• Monitor for unusual AX.25 or NET/ROM network activity patterns
• Configure alerting on kernel oops events related to network subsystems
• Implement regular kernel version auditing to ensure patches are applied

How to Mitigate CVE-2026-23098

Immediate Actions Required

• Update to a patched Linux kernel version containing the fix for CVE-2026-23098
• If immediate patching is not possible, consider disabling NET/ROM protocol support if not required
• Blacklist the netrom kernel module on systems that do not require amateur radio networking
• Monitor systems for signs of exploitation while patches are applied

Patch Information

The Linux kernel development team has released patches to address this vulnerability. The fix adds a NULL check for nr_neigh->ax25 before freeing old_skb in the nr_route_frame() function.

Patches are available through the following kernel git commits:

• Kernel Git Commit 94d1a8b
• Kernel Git Commit 9f5fa78
• Kernel Git Commit ba1096c
• Kernel Git Commit bd89553

Organizations should apply these patches through their distribution's standard kernel update mechanisms.

Workarounds

• Disable the NET/ROM protocol module if not required: modprobe -r netrom
• Prevent automatic loading of the netrom module by adding it to the module blacklist
• Restrict access to raw sockets and amateur radio interfaces to trusted users only
• Implement network segmentation to isolate systems requiring AX.25/NET/ROM support

# Configuration example
# Blacklist the netrom kernel module to prevent loading
echo "blacklist netrom" >> /etc/modprobe.d/blacklist-netrom.conf

# Unload the module if currently loaded
modprobe -r netrom

# Verify the module is not loaded
lsmod | grep netrom