CVE-2026-53199
HighCVSS 7.5Exploitation Probability (EPSS)
Low risk41th percentile — higher than 41% of all known CVEs
Summary
In the Linux kernel, the hv_netvsc driver used phys_to_virt() for mapping memory pages, which on 32-bit x86 with CONFIG_HIGHMEM=y causes memory access faults and system crashes. The fix replaces phys_to_virt() with kmap_local_page() to correctly handle pages outside the kernel direct map.
Risk Assessment
An attacker could exploit this vulnerability to trigger a kernel panic during network packet processing, leading to a denial of service (DoS). The issue affects systems with HIGHMEM enabled on 32-bit x86.
Recommendation
Immediately update the Linux kernel to a version containing the fix (commit with the solution). For production systems, apply the security patch from your distributor.
Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: hv_netvsc: use kmap_local_page in netvsc_copy_to_send_buf netvsc_copy_to_send_buf() copies page buffer entries into the VMBus send buffer using phys_to_virt() on the entry PFN. Entries for the RNDIS header and the skb linear data come from kmalloc'd memory and are always in the kernel direct map, but entries for skb fragments reference page cache or user pages, which on 32-bit x86 with CONFIG_HIGHMEM=y can live above the LOWMEM boundary. For such a page phys_to_virt() returns an address outside the direct map and the subsequent memcpy() faults on the transmit softirq path, which is fatal. Map the pages with kmap_local_page() instead, handling two properties of the page buffer entries: - pb[i].pfn is a Hyper-V PFN at HV_HYP_PAGE_SIZE (4K) granularity, not a native PFN. Reconstruct the physical address first and derive the native page from it, so the mapping stays correct where PAGE_SIZE > HV_HYP_PAGE_SIZE (e.g. arm64 with 64K pages). - Since commit 41a6328b2c55 ("hv_netvsc: Preserve contiguous PFN grouping in the page buffer array"), an entry describes a full physically contiguous fragment and pb[i].len can exceed PAGE_SIZE, while kmap_local_page() maps a single page. Copy page by page, splitting at native page boundaries. The copy path only handles packets smaller than the send section size (6144 bytes by default); larger packets take the cp_partial path where only the RNDIS header is copied. So entries here are bounded by the section size and a copy is split at most once on 4K-page systems. On !CONFIG_HIGHMEM configs kmap_local_page() folds to page_address() and no mapping work is added.