CVE-2026-98025: net: usb: cx82310_eth: drop URB after 0xffff reboot sentinel to prevent partial_data heap overflow
In the Linux kernel, the following vulnerability has been resolved:
net: usb: cx82310eth: drop URB after 0xffff reboot sentinel to prevent partialdata heap overflow
The 0xffff length sentinel detects a router reboot and schedules re-enabling of ethernet mode, but then falls through to the rest of the loop body. The next check is
} else if (len > CX82310MTU) {
which is the else of the just-matched if -- it never fires for len == 0xffff. The MTU bound that normally caps the incomplete-packet save path is silently bypassed.
With 0xffff > skb->len always true (rxurbsize is 4096), the incomplete-packet branch saves dev->partiallen = skb->len bytes into dev->partialdata. partialdata is kmalloc(hardmtu) = kmalloc(CX82310MTU + 2) = 1516 bytes, but skb->len after the 2-byte header pull can be up to 4094. A device that sends a 4096-byte URB starting with [0xff 0xff] therefore copies 4094 device-provided bytes into a buffer allocated for 1516 bytes, exceeding its requested size by 2578 bytes.
The next URB then reads dev->partiallen (4094) back from the same 1516-byte buffer and dev->partialrem (65535 - 4094 = 61441) from the new URB's ~4KB skb, both well past their allocations, and delivers the spliced result as a 64KB "frame" to the network stack.
Bail out of rxfixup after scheduling the re-enable work; the remainder of a reboot-marker URB is not meaningful packet data. This restores the invariant that partiallen < CX82310MTU + 2 on the save path, since every other route there has already passed the MTU check.
Affected Software
Remediation
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Fixed in 6.6.158.1-1 - Upgrade
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In cx82310_eth rx_fixup, after detecting the 0xffff reboot sentinel and scheduling ethernet-mode re-enable work, immediately bail out and drop the URB so the remainder of the reboot-marker URB is not processed as packet data.
Event History
Frequently Asked Questions
Which systems are exposed to this condition?
The issue is in the Linux kernel's cx82310_eth USB Ethernet driver. Exposure requires use of that driver with a device capable of supplying the affected USB receive data.
What input sequence triggers the memory corruption?
A received 4096-byte URB beginning with the two-byte 0xffff reboot sentinel can bypass the normal MTU bound. After the header is removed, up to 4094 bytes are copied into partial_data, which is allocated for 1516 bytes.
What happens after the oversized partial packet is saved?
The copy can exceed the requested partial_data allocation by 2578 bytes. Processing the following URB can then read both the saved partial length and remaining length beyond their respective allocations.