CVE-2026-90063 in Linux
Summary
by MITRE • 09/17/2026
In the Linux kernel, the following vulnerability has been resolved:
virtio-net: Ensure that TCP packets don't overflow gso_segs
The user can specify any gso_size in a packet crafted with an AF_PACKET PACKET_VNET_HDR socket, even smaller than TCP_MIN_GSO_SIZE = 8. At the same time, GSO_MAX_SIZE = 8 * GSO_MAX_SEGS = 8 * 65535. When the user crafts a packet with gso_size < 8, there is a risk for partial GSO to overflow the 16-bit gso_segs field when dividing the SKB length by gso_size.
Adjust gso_size of TCP packets to be at least TCP_MIN_GSO_SIZE = 8. Keep gso_size of UDP GSO packets, as gso_size=1 is valid and explicitly tested at tools/testing/selftests/net/tun.c:649.
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Analysis
by VulDB Data Team • 09/17/2026
The vulnerability identified in the Linux kernel's virtio-net driver represents a critical integer overflow issue within the Generic Segmentation Offload (GSO) subsystem, specifically affecting TCP packet processing. GSO is a performance optimization mechanism that allows higher-layer protocols to pass large data segments to the network interface card for segmentation, thereby reducing CPU overhead during high-throughput networking operations. The core of this flaw lies in the insufficient validation of the gso_size parameter when packets are crafted using an AF_PACKET socket with PACKET_VNET_HDR flags. This configuration permits user-space applications to specify arbitrary segment sizes without adequate bounds checking relative to protocol-specific minimums, creating a pathway for malicious or malformed input to trigger internal kernel miscalculations.
The technical root cause stems from the mathematical relationship between the total packet length and the specified gso_size during segmentation calculations. The Linux kernel defines GSO_MAX_SIZE as eight times GSO_MAX_SEGS, where GSO_MAX_SETS is capped at 65535 to fit within a 16-bit field named gso_segs. When a user supplies a gso_size value smaller than the TCP minimum segment size of eight bytes, the division operation used to calculate the number of segments can result in a quotient that exceeds the maximum capacity of the 16-bit integer. This overflow causes the gso_segs counter to wrap around or assume an incorrect small value, leading to memory corruption, kernel panics, or potentially exploitable conditions where the network stack processes data incorrectly due to misaligned segment boundaries.
From an operational perspective, this vulnerability allows for a denial of service attack against systems relying on virtio-net virtualized networking interfaces. An attacker with access to create AF_PACKET sockets can craft packets that trigger the overflow condition, causing the kernel to crash or behave unpredictably under load. While UDP GSO segments are permitted to have smaller sizes because gso_size=1 is a valid and tested configuration for certain encapsulation scenarios, TCP traffic strictly requires larger minimum segment sizes due to header overheads and protocol constraints. The failure to enforce these distinctions creates an inconsistent security posture where one protocol type is protected while another remains vulnerable to similar exploitation vectors through the same interface mechanism.
Mitigation strategies primarily involve applying kernel patches that explicitly validate gso_size against protocol-specific minima before proceeding with segmentation logic. For TCP packets, the system must ensure that gso_size is never set below TCP_MIN_GSO_SIZE, which is defined as eight bytes in this context. This validation step prevents the division operation from producing results that exceed GSO_MAX_SEGS, thereby preserving the integrity of the 16-bit segment counter. System administrators should prioritize updating to kernel versions where this logic has been corrected and ensure that network virtualization configurations restrict user-space access to raw packet sockets unless absolutely necessary for specific applications like tun/tap devices.
This vulnerability aligns with CWE-190, which describes integer overflow or wraparound errors, as the flaw arises from arithmetic operations exceeding their designated data type limits. Furthermore, it relates to CWE-20 regarding improper input validation, specifically the failure to enforce structural constraints on network packet parameters before processing. In terms of attack classification under MITRE ATT&CK, this issue facilitates potential Denial of Service (T1499) through resource exhaustion or system instability caused by kernel crashes. It also touches upon privilege escalation vectors if the resulting memory corruption can be leveraged to execute arbitrary code within the kernel space, although the primary immediate impact is service disruption and stability degradation for virtualized network environments relying on virtio drivers.