CVE-2026-89949 in Linux
Summary
by MITRE • 09/16/2026
In the Linux kernel, the following vulnerability has been resolved:
batman-adv: dat: avoid unaligned fault in IP extraction
Independent of the alignment of the ARP packet in the SKB, either the batadv_arp_ip_src or the batadv_arp_ip_dst will have an unaligned access (on HW without native unaligned read support).
Use get_unaligned() to handle this properly on all architectures.
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Analysis
by VulDB Data Team • 09/16/2026
The Linux kernel vulnerability identified in the batman-adv module addresses a critical memory alignment issue within the Distributed ARP Table implementation, specifically during IP address extraction from ARP packets. This flaw arises when the kernel attempts to read source or destination IP fields directly from network buffers without ensuring proper data alignment relative to the processor architecture's requirements. On hardware architectures that do not natively support unaligned memory accesses, such as certain ARM variants or older RISC processors, attempting to access a multi-byte integer value at an odd byte offset results in a bus error or general protection fault. This occurs because the batadv_arp_ip_src and batadv_arp_ip_dst functions previously assumed that ARP packets would be aligned in system memory, which is not guaranteed by lower-level network stack implementations where packet headers may start at arbitrary offsets within scatter-gather lists or linearized buffers.
From a technical perspective, this vulnerability represents an improper access of unaligned memory locations, categorized under CWE-1235: Improper Access of Unaligned Memory. The root cause lies in the direct dereferencing of network protocol structures without accounting for potential misalignment introduced by encapsulation layers or packet fragmentation handling within the kernel's networking subsystem. When a batman-adv node processes incoming ARP requests or replies, it extracts IP addresses to update its distributed routing table. If the underlying SKB data buffer is not aligned to a four-byte boundary as expected by standard integer extraction macros on strict-alignment architectures, the CPU generates an exception that crashes the kernel thread handling network traffic. This effectively turns a routine packet processing operation into a local denial of service condition, potentially leading to system instability or reboot depending on how the architecture handles such faults and whether panic-on-exception is enabled in the kernel configuration.
The operational impact of this vulnerability extends beyond simple application crashes, as it affects the stability of mesh networking environments that rely heavily on batman-adv for dynamic routing. An attacker with the ability to inject crafted ARP packets into a network segment connected to a vulnerable node could trigger these unaligned access faults repeatedly, causing sustained denial of service against the mesh infrastructure. This disrupts connectivity for all nodes relying on that particular gateway or backbone router within the mesh topology. Furthermore, in environments where kernel panics are not gracefully handled and result in immediate reboots, this vulnerability can lead to significant downtime and potential data loss if active connections are abruptly terminated without proper teardown procedures. The issue is particularly insidious because it does not require complex exploitation techniques; simply sending standard ARP packets with specific alignment characteristics sufficient to trigger the misalignment on strict-alignment hardware is enough to cause failure.
Mitigation for this vulnerability involves applying kernel patches that replace direct memory access macros with architecture-safe alternatives such as get_unaligned(). This function explicitly handles byte-by-byte copying or uses compiler-specific instructions to safely extract multi-byte values from potentially unaligned addresses, ensuring compatibility across all supported CPU architectures without performance penalties significant enough to impact network throughput. Administrators should ensure their systems are updated with the latest stable kernel versions that include this fix for batman-adv. Additionally, security teams monitoring mesh networks should verify that packet filtering rules do inadvertently expose internal ARP traffic to untrusted segments if such exposure is not intended, although the primary defense remains patching the underlying kernel code to handle memory alignment correctly regardless of input data structure. This update aligns with broader industry efforts to harden network subsystems against edge-case parsing errors and ensures robust operation across diverse hardware deployments ranging from embedded IoT devices running Linux to high-performance server infrastructure utilizing mesh networking for redundancy and load balancing.