CVE-2026-98612 in Linux
Summary
by MITRE • 10/18/2026
In the Linux kernel, the following vulnerability has been resolved:
net: usb: catc: bound the RX packet length in catc_rx_done()
catc_rx_done() walks a multi-packet URB, reading a two-byte length from each packet header. Its bound, pkt_len > urb->actual_length, ignores the header offset and compares against the whole transfer rather than the bytes left from pkt_start, so a crafted packet header makes skb_copy_to_linear_data() read past the buffer.
A length below ETH_HLEN is also accepted, including zero, and eth_type_trans() then reads a MAC header from the uninitialised tailroom of a shorter skb. The is_f5u011 branch takes its length straight from the transfer, so a zero-length URB reaches the same path.
Track the bytes remaining from the current packet, and reject a header that does not fit, a length past what is left, and a length below an Ethernet header.
A transfer shorter than an Ethernet header, including a zero-length one, previously became a runt skb passed to netif_rx() and counted as received; it is now counted in rx_length_errors and ends the walk.
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Analysis
by VulDB Data Team • 10/19/2026
The vulnerability identified within the Linux kernel's USB networking driver for CatC devices stems from improper input validation during the processing of receive packets, specifically within the catc_rx_done function. This routine is responsible for parsing multi-packet Universal Resource Bus (URB) transfers by iterating through packet headers to extract length information and copy data into socket buffers. The core technical flaw lies in how the driver calculates available buffer space before copying packet data. Instead of tracking the remaining bytes within the current URB transfer relative to the current packet start pointer, the code incorrectly compares the extracted two-byte packet length against the total actual length of the entire URB. This oversight ignores the offset already consumed by previous packets or headers in a multi-packet structure, leading to a miscalculation of available memory space.
This logical error results in an out-of-bounds read condition when skb_copy_to_linear_data is invoked with a packet length that exceeds the actual remaining bytes in the buffer but remains within the total URB size limit checked by the flawed logic. Consequently, crafted or malformed USB packets can cause the kernel to read memory beyond the intended boundaries of the socket buffer. Furthermore, the vulnerability includes insufficient validation for minimum packet sizes. The driver accepts packet lengths below the standard Ethernet header length (ETH_HLEN), including zero-length payloads. When such short packets are processed, eth_type_trans attempts to parse a MAC header from uninitialized tailroom data within an undersized skb structure. This exposure can lead to information disclosure by leaking kernel memory contents or potentially trigger undefined behavior depending on how subsequent network stack components handle the malformed frame.
The operational impact of this vulnerability is significant for systems utilizing CatC USB Ethernet adapters, particularly in environments where untrusted or maliciously crafted USB traffic might be introduced into the network interface. An attacker with physical access to the device could craft specific URB transfers that exploit these boundary checks to read arbitrary kernel memory via the out-of-bounds reads. This aligns with CWE-125 (Out-of-bounds Read) and represents a potential vector for information leakage or system instability. In terms of attack patterns, this flaw relates to improper input validation during data processing, which can be categorized under ATT&CK techniques involving resource manipulation or initial access if the USB device is considered an entry point in physical security scenarios. The issue also touches upon CWE-20 (Improper Input Validation) as the driver fails to enforce strict constraints on packet length relative to available buffer space and minimum protocol requirements.
To mitigate this vulnerability, the Linux kernel maintainers have implemented a fix that fundamentally changes how packet boundaries are tracked during URB processing. The updated logic now explicitly tracks the number of bytes remaining from the current packet start position rather than relying on global transfer lengths. This ensures that any header claiming to extend beyond the available data is rejected immediately. Additionally, strict lower bounds are enforced by rejecting packets with a length below ETH_HLEN, thereby preventing eth_type_trans from accessing uninitialized memory in short skbs. Transfers shorter than an Ethernet header, including zero-length URBs, are no longer passed as valid runt frames to netif_rx; instead, they trigger rx_length_errors and terminate the processing walk for that transfer. This correction ensures that only well-formed packets conforming to standard Ethernet specifications proceed through the network stack, effectively neutralizing both the out-of-bounds read risk and the information disclosure vulnerability associated with uninitialized memory access.