CVE-2026-63902: USB: serial: cypress_m8: validate interrupt packet headers
In the Linux kernel, the following vulnerability has been resolved:
USB: serial: cypressm8: validate interrupt packet headers
cypressreadintcallback() parses the interrupt-in buffer according to the selected Cypress packet format. Format 1 has a two-byte status/count header and format 2 has a one-byte combined status/count header. The usb-serial core sizes the interrupt-in buffer from the endpoint descriptor's wMaxPacketSize, and successful interrupt transfers can complete short when URBSHORTNOTOK is not set.
Check that the completed packet contains the selected header before reading it. Malformed short reports are ignored and the interrupt URB is resubmitted through the existing retry path, preventing out-of-bounds header-byte reads.
KASAN report as below: KASAN slab-out-of-bounds in cypressreadintcallback+0x240/0x7f0 Read of size 1 Call trace: cypressreadintcallback() (drivers/usb/serial/cypressm8.c:1009) usbhcdgivebackurb() dummytimer()
[ johan: use constants in header length sanity checks ]
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
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In cypress_read_int_callback(), validate that the completed interrupt packet contains the selected Cypress format's full header before reading it: require a two-byte header for format 1 and a one-byte header for format 2; ignore malformed short reports and resubmit the interrupt URB through the existing retry path.
Event History
Frequently Asked Questions
Which systems are exposed?
Systems running the Linux kernel with the Cypress M8 USB serial driver in use are exposed to malformed short interrupt reports. The affected software list includes Linux kernel packages and Ubuntu kernel variants such as linux, linux-fips, linux-aws, linux-azure, linux-gcp-fips, and related FIPS variants.
What does an attacker need to exploit this issue?
The supplied CVSS vector rates exploitation as local, requiring low privileges and no user interaction. Exploitation involves causing the driver to process a malformed interrupt report that is shorter than the header required by the selected packet format.
What is the likely impact?
The issue can cause an out-of-bounds read in the interrupt callback. The CVSS vector indicates high confidentiality and availability impact, with no integrity impact.
How can I identify signs of this issue?
A kernel built with KASAN may report a slab-out-of-bounds read in cypress_read_int_callback(), with a read of size 1. The reported call path includes cypress_read_int_callback(), __usb_hcd_giveback_urb(), and dummy_timer().