CVE-2026-98408 in Linux
Summary
by MITRE • 10/14/2026
In the Linux kernel, the following vulnerability has been resolved:
watchdog: rzv2h: Avoid division by zero
clk_get_rate() could return 0. Avoid a division by zero panic.
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Analysis
by VulDB Data Team • 10/14/2026
The identified vulnerability resides within the RZ/V2H watchdog driver in the Linux kernel, specifically concerning the handling of clock rates retrieved via the clk_get_rate function. This issue represents a classic arithmetic error where an unchecked input value leads to a critical system failure during runtime operations. The core technical flaw stems from the assumption that hardware clocks will always report a valid, non-zero frequency when queried by the driver. In embedded systems and complex SoC architectures like those based on Renesas RZ/V2H silicon, clock sources can be dynamically disabled, uninitialized, or configured in states where they do not provide an active output signal. Under these conditions, the clk_get_rate function correctly returns zero to indicate that no rate is available, but the watchdog initialization code fails to validate this return value before using it as a divisor for calculating timeout intervals or prescaler values.
When the kernel attempts to perform division by zero in this context, it triggers an immediate panic condition within the executing thread. This results in a denial of service against the entire system, causing an abrupt reboot or hang depending on the specific kernel configuration and crash handling settings. The impact is particularly severe because watchdog drivers are often initialized early during the boot process to ensure system stability monitoring begins as soon as possible. If this initialization fails due to a division by zero exception, it can prevent subsequent subsystems from loading correctly or leave the system in an unstable state where hardware watch dog functionality cannot be established, thereby compromising the reliability guarantees that watchdog timers are designed to provide for embedded and industrial applications.
From a classification perspective, this vulnerability aligns with CWE-369, which describes Divide By Zero errors. It also relates to CWE-252, Checkpoint Failure, as the code fails to properly validate critical preconditions before proceeding with arithmetic operations that depend on those conditions being true. In terms of attack vectors and behavioral mapping under MITRE ATT&CK for Enterprise or ICS, this falls under resource exhaustion or availability impact scenarios where an attacker might exploit misconfigured hardware states or trigger specific power management sequences to force the clock source into a disabled state, thereby inducing the crash remotely if access to the device is possible. While typically requiring local physical or privileged remote access to manipulate hardware configurations, it highlights the importance of robust error handling in low-level system code.
Mitigation strategies primarily involve updating the affected Linux kernel version where this patch has been integrated upstream. The fix implements a defensive programming approach by adding explicit checks for zero return values from clk_get_rate before any division operations are attempted. If a zero rate is detected, the driver should either defer initialization until the clock becomes available or abort with an appropriate error code rather than proceeding to cause a kernel panic. System administrators and developers working on RZ/V2H based platforms must ensure that their firmware configurations do not leave critical watchdog clocks in undefined states during boot sequences. Additionally, implementing static analysis tools capable of detecting potential division by zero conditions can help identify similar vulnerabilities in other parts of the driver stack or related hardware abstraction layers before deployment to production environments.