CVE-2024-26733 is a vulnerability identified in the Linux kernel's ARP (Address Resolution Protocol) implementation, specifically within the arp_req_get() function. This function is invoked when the ioctl system call with the SIOCGARP command is issued, which is used to retrieve ARP table entries. The vulnerability arises due to an overflow in the memcpy operation that copies the hardware address (neigh->ha) into the arpreq structure's arp_ha.sa_data field. The arp_ha field is defined as a struct sockaddr, which allocates only 14 bytes for sa_data. However, the memcpy operation attempts to copy more bytes than this buffer can hold, particularly when the device's address length (dev->addr_len) exceeds 22 bytes, such as when MAX_ADDR_LEN is used. This overflow can overwrite adjacent fields in the arpreq structure, notably arp_flags and arp_netmask. Although the arp_flags field is initialized immediately after the memcpy, preventing immediate corruption, the overflow into arp_netmask can lead to incorrect values being set, potentially affecting ARP behavior. The vulnerability was detected by the syzkaller fuzzing tool, which reported a field-spanning write warning. The root cause is the mismatch between the fixed size of sa_data and the variable length of hardware addresses. The Linux kernel commit referenced (b5f0de6df6dc) attempted to silence the syzkaller warning by converting sa_data to a flexible array, but this did not fully resolve the underlying overflow risk. The fix involves limiting the maximum length of the memcpy operation to prevent overflow beyond the 14-byte buffer. This vulnerability affects Linux kernel versions prior to the patch and can be triggered by local users issuing ioctl calls to retrieve ARP entries. The detailed kernel stack trace and debugging information confirm the overflow occurs at net/ipv4/arp.c line 1128. No known exploits are reported in the wild as of the publication date (April 3, 2024).

For European organizations, this vulnerability poses a moderate risk primarily in environments where local users or processes can issue ioctl calls to the kernel's networking stack. Exploitation could lead to memory corruption within the kernel space, potentially causing system instability, crashes (denial of service), or in some cases, escalation of privileges if the overflow can be leveraged to execute arbitrary code. Given that ARP is fundamental to network communication, any disruption or manipulation could affect network reliability and security. Systems running Linux kernels with affected versions, especially those with network devices having hardware addresses longer than 22 bytes, are at risk. This includes servers, network appliances, and embedded devices commonly used in European enterprises and critical infrastructure. The vulnerability does not require remote network access or user interaction beyond local ioctl invocation, limiting its exposure to local attackers or compromised accounts. However, in multi-tenant or shared environments such as cloud providers or hosting services prevalent in Europe, the risk of lateral movement or privilege escalation increases. The absence of known exploits reduces immediate threat but patching is critical to prevent future exploitation. Disruption of ARP functionality could also impact network operations in sectors like finance, manufacturing, and telecommunications, which are vital to European economies.

European organizations should prioritize updating their Linux kernel to the latest patched versions that include the fix for CVE-2024-26733. Specifically, ensure that kernels are updated beyond the commit that limits the memcpy length in arp_req_get(). For environments where immediate patching is not feasible, restrict access to ioctl system calls related to ARP by enforcing strict user permissions and using security modules like SELinux or AppArmor to limit capabilities of untrusted processes. Network devices with hardware addresses exceeding standard lengths should be audited and monitored closely. Employ kernel hardening techniques such as Kernel Address Space Layout Randomization (KASLR) and Kernel Page Table Isolation (KPTI) to reduce exploitation potential. Additionally, implement runtime monitoring for unusual ioctl calls or kernel crashes that could indicate attempted exploitation. For cloud and multi-tenant environments, isolate workloads and enforce strict privilege separation to minimize impact. Regularly review and update intrusion detection systems to recognize anomalous kernel behavior related to ARP operations. Finally, maintain an incident response plan that includes kernel vulnerability management and rapid patch deployment.