CVE-2026-81009
Low risk· EPSS 6%Exploitation Probability (EPSS)
Low risk6th percentile - higher than 6% of all known CVEs
Summary
In the Linux kernel, io_handle_query_entry() in the io_uring subsystem clamps hdr.size for the inbound copy_from_user() but keeps the original user value as usize. copy_struct_to_user() uses that usize and may zero out nearly 4 GiB, including on the error path. The interface is reachable without a ring via IORING_REGISTER_QUERY.
Risk Assessment
Excessive zeroing of memory (up to ~4 GiB) can be triggered, potentially leading to denial of service or system destabilization. The vulnerability is locally reachable without special privileges.
Recommendation
Update the Linux kernel to a version that rejects sizes larger than PAGE_SIZE in copy_struct_* interfaces. Consider restricting access to IORING_REGISTER_QUERY for unprivileged users.
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Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: io_uring/query: cap user size passed to copy_struct_to_user io_handle_query_entry() clamps hdr.size for the inbound copy_from_user() but keeps the original user value as usize. copy_struct_to_user() uses that usize and, when it is larger than the kernel result, clear_user()s the trailing bytes. As hdr.size is a __u32, a query can request nearly 4 GiB of zeroing, including on the error path where res_size stays 0. The interface is reachable without a ring via IORING_REGISTER_QUERY. Reject sizes larger than PAGE_SIZE, as recommended for copy_struct_* interfaces.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS

