CVE-2025-68211 Affecting kernel-rt-kvm package, versions *
Threat Intelligence
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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Test your applications- Snyk IDSNYK-CENTOS8-KERNELRTKVM-14514428
- published18 Dec 2025
- disclosed16 Dec 2025
Introduced: 16 Dec 2025
NewCVE-2025-68211 (opens in a new tab)How to fix?
There is no fixed version for Centos:8 kernel-rt-kvm.
NVD Description
Note: Versions mentioned in the description apply only to the upstream kernel-rt-kvm package and not the kernel-rt-kvm package as distributed by Centos.
See How to fix? for Centos:8 relevant fixed versions and status.
In the Linux kernel, the following vulnerability has been resolved:
ksm: use range-walk function to jump over holes in scan_get_next_rmap_item
Currently, scan_get_next_rmap_item() walks every page address in a VMA to locate mergeable pages. This becomes highly inefficient when scanning large virtual memory areas that contain mostly unmapped regions, causing ksmd to use large amount of cpu without deduplicating much pages.
This patch replaces the per-address lookup with a range walk using walk_page_range(). The range walker allows KSM to skip over entire unmapped holes in a VMA, avoiding unnecessary lookups. This problem was previously discussed in [1].
Consider the following test program which creates a 32 TiB mapping in the virtual address space but only populates a single page:
#include <unistd.h> #include <stdio.h> #include <sys/mman.h>
/* 32 TiB */ const size_t size = 32ul * 1024 * 1024 * 1024 * 1024;
int main() { char *area = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_NORESERVE | MAP_PRIVATE | MAP_ANON, -1, 0);
if (area == MAP_FAILED) { perror("mmap() failed\n"); return -1; }/* Populate a single page such that we get an anon_vma. */ *area = 0; /* Enable KSM. */ madvise(area, size, MADV_MERGEABLE); pause(); return 0;
}
$ ./ksm-sparse & $ echo 1 > /sys/kernel/mm/ksm/run
Without this patch ksmd uses 100% of the cpu for a long time (more then 1 hour in my test machine) scanning all the 32 TiB virtual address space that contain only one mapped page. This makes ksmd essentially deadlocked not able to deduplicate anything of value. With this patch ksmd walks only the one mapped page and skips the rest of the 32 TiB virtual address space, making the scan fast using little cpu.