CVE-2026-99266 in Linux
Summary
by MITRE • 11/03/2026
In the Linux kernel, the following vulnerability has been resolved:
io_uring/napi: make stale entries time out after 60s
With dynamic tracking a NAPI id that hasn't been seen for a minute is meant to be dropped from the list the ring busy polls. The timeout is added to jiffies, but it is defined as 60 * SEC_CONVERSION, and SEC_CONVERSION isn't the number of jiffies in a second. It is the internal factor of __timespec64_to_jiffies(), HZ scaled up by SEC_JIFFIE_SC bits. For HZ=1000 that is 1000 << 22, which puts the timeout at about eight years. On 32-bit the multiplication overflows.
So entries are never removed, and every id that a socket of the ring ever had keeps being polled on each wait.
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Analysis
by VulDB Data Team • 11/04/2026
The Linux kernel io_uring subsystem contains a critical logic error in its Network API polling mechanism that results in resource exhaustion due to an incorrect timeout calculation for stale NAPI entries. The vulnerability stems from a misuse of internal time conversion constants within the dynamic tracking logic designed to manage busy-polling rings. Specifically, when determining whether a Network API identifier has remained inactive long enough to be considered stale and removed from the polling list, the code adds sixty times SEC_CONVERSION to the current jiffies value. This approach fundamentally misunderstands how kernel timekeeping works, as SEC_CONVERSION is not a direct multiplier for converting seconds into jiffies but rather an internal scaling factor used by the __timespec64_to_jiffies() function that accounts for system clock frequency and bit-shifting operations.
On systems configured with a standard timer interrupt rate of one thousand hertz, this error results in a timeout value approximately equal to eight years rather than sixty seconds. The calculation involves shifting values by twenty-two bits, which creates an astronomically large number when interpreted as jiffies. Furthermore, on thirty-two-bit architectures, the multiplication operation suffers from integer overflow, potentially resulting in negative or wrap-around time values that further disrupt the logical comparison used to identify stale entries. Consequently, the condition required to trigger the removal of these entries is never met under normal operational conditions, causing the kernel to retain references to network interfaces indefinitely.
The operational impact of this flaw is significant resource consumption and potential denial of service for applications utilizing io_uring with busy-polling enabled on sockets. Since stale NAPI identifiers are never pruned from the polling list, every wait operation associated with a ring that has ever interacted with a specific socket will continue to poll those interfaces regardless of their current activity status. This leads to unnecessary CPU cycles being consumed in tight loops checking for network events on inactive or irrelevant hardware contexts. Over time, as more sockets are opened and closed by applications using io_uring, the polling list grows unbounded, increasing latency for legitimate operations and degrading overall system performance due to cache pollution and processor contention.
This vulnerability aligns with CWE-787 Out-of-bounds Write in terms of memory management implications if the growth leads to allocation failures, but more accurately reflects CWE-390 Detection of Error Condition Without Action or CWE-401 Missing Release of Memory after Effective Lifetime when considering the failure to release resources. In the context of the MITRE ATT&CK framework, this behavior can be leveraged for Denial of Service by exhausting system resources such as CPU time and memory structures associated with network polling lists. Attackers could potentially trigger this condition rapidly by creating numerous io_uring instances that open and close sockets in quick succession to populate the stale entry list without ever allowing them to age out properly, thereby causing a sustained degradation of service for other processes on the host.
Mitigation strategies primarily involve applying kernel patches that correct the time conversion logic to use proper jiffies arithmetic rather than raw multiplication with SEC_CONVERSION. System administrators should ensure their Linux kernels are updated to versions where this io_uring NAPI timeout fix has been integrated, typically found in stable release branches following the identification of the bug. For environments unable to immediately patch, limiting the number of concurrent busy-polling sockets or disabling busy-polling for network interfaces can reduce the rate at which stale entries accumulate and mitigate the immediate performance impact until a permanent code correction is deployed across all affected systems.