CVE-2026-72238 in Linux
Summary
by MITRE • 08/15/2026
In the Linux kernel, the following vulnerability has been resolved:
x86/boot: Validate console=uart8250 baud rate to fix early boot hang
When the baud rate is empty, 0, invalid, or overflows to 0 when stored as an int, the system will hang during early boot because of a division by zero in early_serial_init().
Fall back to DEFAULT_BAUD when the resulting baud rate is 0 to prevent an early system hang.
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Analysis
by VulDB Data Team • 08/15/2026
This vulnerability exists within the x86 boot process of the Linux kernel where improper validation of console parameters leads to system hang during early boot phases. The issue specifically affects the uart8250 console driver initialization routine known as early_serial_init() which performs division operations without adequate input sanitization. When the console=uart8250 parameter receives an empty, zero, or invalid baud rate value, the system attempts to compute a division by zero operation during boot sequence resulting in complete system hang. This represents a classic denial of service condition that prevents normal system operation before any user-space processes can execute.
The technical flaw stems from insufficient parameter validation within the early boot initialization code where baud rate values are accepted without proper range checking or type validation. When an invalid baud rate is provided through the console parameter, it gets processed and stored as an integer value which can overflow to zero, triggering the division by zero exception in early_serial_init(). This condition occurs during the critical early boot phase when kernel initialization routines are executing before normal error handling mechanisms are fully available. The vulnerability manifests as a complete system freeze rather than a recoverable error condition.
The operational impact of this vulnerability is severe as it affects all Linux systems using x86 architecture that attempt to boot with invalid console=uart8250 parameters. Systems may become completely unresponsive during boot, requiring physical intervention or forced reboot mechanisms to regain access. This vulnerability particularly affects embedded systems, servers, and virtual machines where automated boot processes are common and manual intervention is limited. The hang occurs before any logging or diagnostic information can be generated, making it difficult to identify the root cause through standard troubleshooting methods.
The fix implemented addresses this issue by introducing a fallback mechanism that detects when the computed baud rate equals zero and automatically reverts to a predefined DEFAULT_BAUD value instead of allowing the system to proceed with invalid configuration. This remediation follows established security practices for input validation and graceful error handling in kernel space operations. The solution prevents the division by zero condition while maintaining backward compatibility with valid console configurations. This approach aligns with common security principles outlined in CWE-362 related to concurrent execution during initialization phases, and represents a defensive programming technique similar to those recommended in MITRE ATT&CK framework for kernel-level privilege escalation prevention. The implementation ensures that early boot processes remain robust against malformed input parameters while preserving system availability during critical initialization stages.