CVE-2024-26635 is a vulnerability identified in the Linux kernel's Logical Link Control (LLC) networking code. The root cause stems from improper handling of the deprecated Ethernet protocol type ETH_P_TR_802_2 (0x0011), which was originally used for Token Ring networks. The vulnerability arises because the Linux kernel code removed special processing for Token Ring packets but failed to fully disable acceptance of ETH_P_TR_802_2 packets. Specifically, local variables representing source and destination MAC addresses (saddr, daddr) are only initialized when the packet protocol is ETH_P_802_2 (0x0004). If a packet with ETH_P_TR_802_2 protocol is processed, these variables remain uninitialized, leading to the use of uninitialized memory in the __llc_lookup_established() and __llc_lookup_listener() functions. This can cause undefined behavior, including potential memory corruption or information leakage. The vulnerability was discovered and reported by syzbot, an automated kernel fuzzing tool, which triggered the bug by sending crafted packets using the deprecated protocol. The issue was introduced after commit 211ed865108e, which removed Token Ring support but left a code path open for ETH_P_TR_802_2 packets to be processed incorrectly. The fix involves dropping support for ETH_P_TR_802_2 entirely and ensuring no uninitialized variables are used during LLC packet processing. No known exploits are currently reported in the wild. The vulnerability affects Linux kernel versions containing the referenced commit and likely subsequent versions until patched. Since this is a kernel-level flaw in network packet processing, it could be triggered remotely if an attacker can send crafted packets to a vulnerable system's network interface, particularly if the system processes LLC frames or uses virtual network interfaces like TUN/TAP, as indicated by the stack trace. However, exploitation complexity may be higher due to the need to craft specific packet types and the deprecated nature of the protocol. No CVSS score is assigned yet.

For European organizations, this vulnerability poses a moderate risk primarily to systems running vulnerable Linux kernel versions that have not applied the patch removing ETH_P_TR_802_2 support. The impact includes potential kernel memory corruption or information leakage, which could lead to denial of service (system crashes) or potentially privilege escalation if combined with other vulnerabilities. Since the flaw is in the kernel's network stack, exposed network-facing Linux servers, virtualized environments using TUN/TAP interfaces, and embedded devices running Linux kernels with this vulnerability are at risk. European enterprises with critical infrastructure, cloud providers, and telecommunications operators relying on Linux-based systems could face service disruptions or targeted attacks exploiting this flaw. The risk is heightened in environments where unfiltered network traffic or legacy protocols might be present. However, the lack of known exploits and the deprecated protocol's rarity reduce immediate widespread exploitation risk. Still, the vulnerability should be addressed promptly to prevent future exploitation, especially in sectors with high security requirements such as finance, energy, and government services across Europe.

1. Immediate patching: Apply the latest Linux kernel updates that remove support for ETH_P_TR_802_2 and fix the uninitialized variable usage. Monitor vendor advisories for backported patches if using long-term support kernels. 2. Network filtering: Implement network-level filtering to block or drop packets with the ETH_P_TR_802_2 protocol type on perimeter and internal firewalls to reduce exposure. 3. Disable unused protocols: Audit and disable legacy or deprecated network protocols and interfaces that are not required in your environment, minimizing attack surface. 4. Harden virtual interfaces: For virtualized environments using TUN/TAP devices, ensure they are updated and properly configured to prevent injection of crafted packets exploiting this vulnerability. 5. Monitoring and detection: Deploy kernel integrity monitoring and network anomaly detection to identify unusual LLC traffic or kernel crashes that may indicate exploitation attempts. 6. Incident response readiness: Prepare to respond to potential denial of service or kernel panic incidents by maintaining backups and recovery procedures for critical Linux systems. 7. Vendor coordination: Engage with Linux distribution vendors to confirm patch availability and deployment timelines, especially for embedded or specialized Linux systems common in industrial or telecom sectors.