UBUNTU-CVE-2026-80827: Medium severity ubuntu/linux vulnerability
In the Linux kernel, the following vulnerability has been resolved: USB: serial: option: fix slab OOB read in interrupt URB callback The interrupt URB buffer is allocated in setupportinterruptin() based on the endpoint's wMaxPacketSize: buffersize = usbendpointmaxp(epd); port->interruptinbuffer = kmalloc(buffersize, GFPKERNEL); When a USB device declares wMaxPacketSize = 8 on its interrupt IN endpoint, the buffer is allocated from kmalloc-8 cache (exactly 8 bytes). If the device sends a short packet (actuallength < wMaxPacketSize), the URB completes with status == 0 and the callback proceeds to read: data[sizeof(struct usbctrlrequest)] which evaluates to data[8], accessing 1 byte beyond the allocated 8-byte buffer. This results in a slab out-of-bounds read. Fix this by adding the missing bounds check: first verify that the actual length is large enough to contain the struct usbctrlrequest header before accessing reqpkt->bRequestType and reqpkt->bRequest, and then verify that there is an additional byte for the modem signal state before reading data[sizeof(struct usbctrlrequest)] inside the conditional. Use sizeof(reqpkt) instead of sizeof(struct usbctrlrequest) for consistency. [ johan: use deverr(); split signals declaration and initialisation ]
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
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In the USB serial option interrupt URB callback, verify that actual_length is at least sizeof(*req_pkt) before accessing req_pkt->bRequestType or req_pkt->bRequest, then verify that actual_length includes one additional byte before reading data[sizeof(*req_pkt)] for the modem signal state; use sizeof(*req_pkt) instead of sizeof(struct usb_ctrlrequest).
Event History
Frequently Asked Questions
What does an attacker need to exploit this issue?
An attacker would need to cause the option USB serial driver to process an interrupt IN transfer from a USB device that declares an 8-byte maximum packet size and sends a shorter packet. The vulnerable callback must run with a successful URB completion.
Which systems are potentially exposed?
Systems using the listed Ubuntu kernel packages may be exposed when the option USB serial driver handles a qualifying USB device. The provided data does not identify affected package versions or whether the driver is enabled by default.