CVE-2026-53321 in Linux
Summary
by MITRE • 06/26/2026
In the Linux kernel, the following vulnerability has been resolved:
io_uring/napi: cap busy_poll_to 10 msec
Currently there's no cap on the maximum amount of time that napi is allowed to poll if no events are found, which can lead to kernel complaints on a task being stuck as there's no conditional rescheduling done within that loop.
Just cap it to 10 msec in total, that's already way above any kind of sane value that will reap any benefits, yet low enough that it's nowhere near being able to trigger preemption complaints.
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Analysis
by VulDB Data Team • 06/26/2026
The vulnerability identified in the Linux kernel relates to improper resource management within the io_uring subsystem and Network API (napi) polling mechanism. This issue stems from the absence of a maximum time limit on how long napi can continue polling for events when no work is available, creating a potential for system instability and performance degradation. The flaw exists in the kernel's event handling infrastructure where polling loops lack proper conditional rescheduling mechanisms that would allow other tasks to execute during idle periods.
The technical implementation of this vulnerability involves the io_uring subsystem's interaction with napi, which is responsible for processing network interrupts and maintaining efficient data transfer operations. When no events are detected during polling cycles, the system continues to consume CPU resources without yielding control to other processes or threads. This behavior violates fundamental kernel design principles that require proper time-slicing and resource management to prevent starvation of critical system tasks.
From an operational impact perspective, this vulnerability can lead to significant performance degradation where the kernel becomes unresponsive to other scheduling requirements. The lack of time limits on polling operations can cause kernel complaints about tasks appearing stuck, which may trigger system stability issues or prevent proper preemption of long-running processes. This condition is particularly problematic in high-throughput environments where io_uring and network processing are heavily utilized.
The mitigation strategy implemented addresses this by establishing a hard cap of 10 milliseconds on total busy polling time within the napi loop. This solution aligns with established security practices for preventing resource exhaustion attacks and maintaining system responsiveness. The chosen limit of 10 milliseconds provides sufficient time to process any pending work while ensuring that no single polling cycle can monopolize system resources long enough to trigger preemption complaints or cause system instability.
This vulnerability classification maps to CWE-704 in the Common Weakness Enumeration framework, specifically addressing improper resource management and lack of proper time limits on processing cycles. The fix demonstrates adherence to security best practices outlined in various kernel hardening guidelines and follows the principle of least privilege by ensuring that no single subsystem can consume excessive resources indefinitely. The solution also aligns with ATT&CK technique T1496 which involves resource exhaustion attacks, as it prevents potential denial-of-service scenarios through improper polling behavior.
The implementation of this cap represents a defensive programming approach that balances system efficiency with resource management principles. By establishing clear boundaries on polling duration, the kernel maintains its responsiveness to other scheduling requirements while still allowing io_uring operations to function effectively. This compromise ensures that legitimate performance optimizations are preserved while preventing the system from entering unstable states due to unbounded polling loops.
This fix exemplifies proper kernel security engineering practices where resource management is carefully balanced with functional requirements. The 10 millisecond cap provides a safety margin that exceeds typical performance optimization needs while remaining well within bounds that would not cause noticeable impact on system responsiveness or user experience. The solution demonstrates the importance of implementing proper time limits and conditional rescheduling mechanisms in kernel-level code to prevent resource exhaustion scenarios and maintain overall system stability.
The vulnerability resolution also reflects broader security principles found in industry standards for kernel development, where defensive measures are implemented to prevent both accidental resource exhaustion and potential exploitation through carefully crafted denial-of-service attacks. This approach ensures that even under adverse conditions or malicious input, the kernel maintains predictable behavior and resource usage patterns that align with established security frameworks and operational requirements for enterprise and production environments.