CVE-2026-63877

Medium · 5.5

CVSS

5.5

EPSS

0.2%

Published

Jul 19, 2026

CISA due date

—

Cloudanix analysis

Schedule a fix SSVC: Track

An old serial-port driver on certain outdated computers can crash the whole machine right when it turns on.

Exploitation: Local Privilege
Attacker needs: Local User
Complexity: Low
Impact: Denial Of Service
Component: OS kernel
Class: Memory Corruption
Remediation: Upgrade
Effort: Medium
Patch risk: Low

What it actually does

Null pointer dereference in the DZ serial driver during early kernel initialization when legacy probing supplies no parent device, causing an invalid memory access in __dev_fwnode and an immediate kernel oops.

Why it matters to the business

Systems using the affected DECstation hardware fail to complete boot, resulting in complete loss of availability until the kernel is updated or the driver is disabled.

How an attack unfolds

An attacker triggers early boot on vulnerable hardware; the DZ driver registers its port via serial_core_register_port, which calls serial_base_ctrl_add and dereferences a null fwnode pointer, crashing the kernel before user space starts.

How to fix it

Update the Linux kernel to a version containing the platform device conversion for the DZ driver; rebuild and deploy the fixed kernel image, ensuring platform_driver_probe is used and resource spans are correctly requested.

How to confirm the fix worked

Boot the updated kernel on target hardware and confirm the DZ driver binds via platform device without producing the paging-request oops; inspect dmesg for successful fb0 and serial registration messages.

Typical attack path

Gain ability to initiate or observe kernel boot on affected DECstation hardware
Allow the DZ driver to execute its legacy init path during do_one_initcall
Trigger the null dereference in __dev_fwnode called from serial_base_ctrl_add

How to detect it

Search kernel logs and early-boot traces for the exact oops signature involving __dev_fwnode, serial_base_ctrl_add, and a paging request at address 000000bc during swapper/0 init.

__dev_fwnode+0x0/0xc
serial_base_ctrl_add+0xa0/0x168
Unable to handle kernel paging request at virtual address 000000bc
dz_init+0x74/0xc8

What your security team should do

Prioritize kernel upgrade on any remaining DECstation or legacy MIPS systems
Add early-boot kernel log monitoring for DZ-related oops patterns
Disable the DZ driver at build time if the hardware is decommissioned

The record

In the Linux kernel, the following vulnerability has been resolved: serial: dz: Convert to use a platform device Prevent a crash from happening as the first serial port is initialised: Console: switching to colour frame buffer device 160x64 tgafb: SFB+ detected, rev=0x02 fb0: Digital ZLX-E1 frame buffer device at 0x1e000000 DECstation DZ serial driver version 1.04 CPU 0 Unable to handle kernel paging request at virtual address 000000bc, epc == 8048b3a4, ra == 80470a78 Oops[#1]: CPU: 0 UID: 0 PID: 1 Comm: swapper/0 Not tainted 6.19.0-dirty #35 NONE $ 0 : 00000000 1000ac00 00000004 804707ac $ 4 : 00000000 80e20850 80e20858 81000030 $ 8 : 00000000 8072c81c 00000008 fefefeff $12 : 6c616972 00000006 80c5917f 69726420 $16 : 80e20800 00000000 808f8968 80e20800 $20 : 00000000 807f5a90 808b0094 808d3bc8 $24 : 00000018 80479030 $28 : 80c2e000 80c2fd70 00000069 80470a78 Hi : 00000004 Lo : 00000000 epc : 8048b3a4 __dev_fwnode+0x0/0xc ra : 80470a78 serial_base_ctrl_add+0xa0/0x168 Status: 1000ac04 IEp Cause : 30000008 (ExcCode 02) BadVA : 000000bc PrId : 00000220 (R3000) Modules linked in: Process swapper/0 (pid: 1, threadinfo=(ptrval), task=(ptrval), tls=00000000) Stack : 00400044 00400040 8046f4cc 00000000 808a6148 808a0000 808f8968 8086983c 808e0000 8046fc84 1000ac01 00000028 80e20700 802ba3f8 80e20700 80d34a94 80c1b900 80e20700 80e20700 80e20700 80e20700 80444650 00000000 00000000 00000000 807f5a90 808b0094 80447080 00400040 808e0000 80d34a94 808a6148 80d34a94 00000004 80e20700 00000000 8076974c 80469810 80c2fe3c 1000ac01 ... Call Trace: [<8048b3a4>] __dev_fwnode+0x0/0xc [<80470a78>] serial_base_ctrl_add+0xa0/0x168 [<8046fc84>] serial_core_register_port+0x1c8/0x974 [<808c6af0>] dz_init+0x74/0xc8 [<800470e0>] do_one_initcall+0x44/0x2d4 [<808b111c>] kernel_init_freeable+0x258/0x308 [<8072e434>] kernel_init+0x20/0x114 [<80049cd0>] ret_from_kernel_thread+0x14/0x1c Code: 27bd0018 03e00008 2402ffea <8c8200bc> 03e00008 00000000 27bdffc0 afbe0038 afb30024 ---[ end trace 0000000000000000 ]--- -- where a pointer is dereferenced that has been derived from a null pointer to the port's parent device. Since no device is available with legacy probing and it's not anymore a preferable way to discover devices anyway, switch the driver to using a platform device and use it as the port's parent device. Update resource handling accordingly and only request the actual span of addresses used within the slot, which will have had its resource already requested by generic platform device code. Use platform_driver_probe() not just because the DZ device is fixed with solder on board and not straightforward to remove, but foremost because the associated TTY's major device number is the same as used by the zs driver and the first driver to claim it will prevent the other one from using it. Either one DZ device or some SCC devices will be present in a given system but never both at a time, and therefore we want the major device number to be claimed by the first driver to actually successfully bind to its device and platform_driver_probe() is a way to fulfil that. An unfortunate consequence of the switch to a platform device is we now hand the console over from the bootconsole much later in the bootstrap. The firmware console handler appears good enough though to work so late and in particular with interrupts enabled. Conversely only starting the console port so late lets the reset code fully utilise our delay handlers, so switch from udelay() to fsleep() for transmitter draining so as to avoid busy-waiting for an excessive amount of time.

Affected packages

Ecosystem	Package	Introduced	Fixed