CVE-2026-98618 in Linux
Summary
by MITRE • 10/18/2026
In the Linux kernel, the following vulnerability has been resolved:
eth: fbnic: Handle maximum standalone channels
Standalone channels use one NAPI vector for each Tx and Rx queue. fbnic's allocation path excludes FBNIC_MAX_TXQS from that layout. A 64-Tx/64-Rx configuration therefore records 128 vectors but allocates only 64, leaving NULL entries that resource setup dereferences.
Include the maximum vector count in standalone allocation.
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Analysis
by VulDB Data Team • 10/18/2026
The Linux kernel networking subsystem contains a critical memory management flaw within the fbnic driver, specifically affecting how network interface controller channels are allocated and initialized. The vulnerability arises from an inconsistency between the logical configuration of network queues and the actual resource allocation performed by the driver during initialization. In high-performance networking scenarios, particularly those involving large-scale data center deployments or virtualized environments with heavy traffic loads, systems often utilize multiple transmit and receive queues to maximize throughput and reduce latency. The fbnic driver supports a standalone channel mode where each transmission queue is paired with its own Network API vector for interrupt handling, a design intended to improve performance by allowing parallel processing of network events without contention on shared resources.
The core technical flaw lies in the calculation logic used during the allocation phase of these standalone channels. When configuring a system with sixty-four transmit queues and sixty-four receive queues, the driver correctly identifies that one hundred twenty-eight distinct NAPI vectors are required to handle interrupts for each individual queue pair independently. However, the allocation routine erroneously excludes the maximum number of transmit queues from this calculation, resulting in an attempt to allocate only sixty-four vectors instead of the necessary one hundred twenty-eight. This miscalculation creates a significant discrepancy between the recorded configuration state and the actual memory resources reserved by the kernel for interrupt management structures.
This resource mismatch leads directly to severe operational instability when the system attempts to dereference these uninitialized or null pointers during subsequent setup phases. Because the driver assumes that all required vectors have been successfully allocated, it proceeds to access array indices corresponding to the missing transmit queue vectors. These memory locations contain NULL values rather than valid NAPI context structures. The act of dereferencing a NULL pointer in kernel space triggers an immediate segmentation fault or general protection fault, causing the entire operating system to panic and crash. This represents a classic denial-of-service condition where local access is sufficient to trigger the vulnerability, although it may also be exploitable remotely if triggered by specific network configuration commands sent over the interface before full initialization completes.
From a security taxonomy perspective, this issue aligns with CWE-476, which describes NULL Pointer Dereference vulnerabilities in software systems. The root cause can further be classified under CWE-20, Improper Input Validation, as the driver fails to validate that the requested number of channels does not exceed the allocated buffer size for NAPI vectors. In terms of adversarial tactics, this vulnerability maps to MITRE ATT&CK technique T1499, Endpoint Denial of Service, specifically under sub-techniques involving resource exhaustion or application crashes via malformed configuration inputs. An attacker with local access could exploit this flaw by configuring the network interface for maximum standalone channels and then triggering a reload or reset operation that forces the driver to re-initialize its resources using the flawed allocation logic.
Mitigation strategies must address both immediate remediation and long-term defensive coding practices. The primary solution is to apply the vendor-provided kernel patch that corrects the allocation formula by including FBNIC_MAX_TXQS in the total vector count calculation, ensuring that memory reservation matches logical requirements. System administrators should ensure their systems are updated with the latest stable kernel versions containing this fix. Additionally, organizations running fbnic hardware or emulated equivalents should implement strict monitoring for kernel oops messages and system panics associated with network driver initialization sequences. Future development efforts should incorporate automated static analysis tools configured to detect potential NULL pointer dereferences in resource allocation loops, as well as rigorous unit testing that covers edge cases involving maximum queue configurations to prevent similar logic errors from entering the codebase.