CVE-2026-23098 in Linux
Summary
by MITRE • 02/04/2026
In the Linux kernel, the following vulnerability has been resolved:
netrom: fix double-free in nr_route_frame()
In nr_route_frame(), old_skb is immediately freed without checking if nr_neigh->ax25 pointer is NULL. Therefore, if nr_neigh->ax25 is NULL, the caller function will free old_skb again, causing a double-free bug.
Therefore, to prevent this, we need to modify it to check whether nr_neigh->ax25 is NULL before freeing old_skb.
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Analysis
by VulDB Data Team • 05/03/2026
The vulnerability identified as CVE-2026-23098 represents a critical double-free error within the Linux kernel's NetROM networking subsystem. This issue specifically affects the nr_route_frame() function which handles routing of network frames within the AX.25 packet radio network protocol implementation. The flaw manifests when the function processes network packets and attempts to free memory resources without proper validation of pointer states. The vulnerability occurs in the context of network packet processing where the kernel must manage memory allocation and deallocation for network frame buffers during routing operations.
The technical root cause of this vulnerability lies in the improper memory management logic within the nr_route_frame() function. When processing network frames, the function immediately frees the old_skb buffer without first verifying whether the nr_neigh->ax25 pointer is NULL. This pointer typically contains a reference to an AX.25 network neighbor structure that may be in an inconsistent state. When nr_neigh->ax25 evaluates to NULL, the function proceeds to free old_skb, but subsequent code execution in the calling function attempts to free the same memory location again, resulting in a double-free condition that can corrupt the kernel's memory management structures.
This double-free vulnerability presents significant operational impact within the Linux kernel environment, particularly in systems utilizing AX.25 networking protocols for packet radio communications. The memory corruption resulting from the double-free can lead to arbitrary code execution, system crashes, or denial of service conditions that compromise system stability. The vulnerability is particularly concerning because it occurs within kernel space network processing code, meaning that exploitation could allow attackers to escalate privileges or cause system-wide failures. The flaw affects any Linux system running kernel versions containing the vulnerable NetROM implementation, potentially impacting specialized communication systems, amateur radio networks, and embedded systems utilizing AX.25 protocols.
The remediation for this vulnerability requires implementing a simple but crucial pointer validation check before memory deallocation occurs. The fix involves modifying the nr_route_frame() function to explicitly check whether nr_neigh->ax25 is NULL before proceeding with the free operation on old_skb. This approach aligns with established security practices for preventing double-free vulnerabilities and follows the principle of defensive programming. The solution directly addresses the core issue identified by CWE-415, which specifically covers double free conditions in software implementations. From an operational security perspective, this fix represents a minimal but essential change that prevents memory corruption while maintaining the intended functionality of the NetROM routing subsystem. The mitigation strategy also aligns with ATT&CK technique T1068, which covers local privilege escalation through kernel vulnerabilities, as the fix prevents exploitation that could lead to unauthorized system access.
This vulnerability demonstrates the critical importance of proper memory management in kernel space operations and highlights how seemingly simple pointer validation can prevent catastrophic system failures. The fix serves as a reminder of fundamental security principles that should be applied throughout kernel development, particularly in networking subsystems where memory allocation patterns are complex and error-prone. The resolution of CVE-2026-23098 through this targeted pointer validation approach represents a standard security patch that should be applied across all affected Linux kernel installations to maintain system integrity and prevent potential exploitation by malicious actors targeting network infrastructure components.