{
  "threat_severity" : "Moderate",
  "public_date" : "2025-12-16T00:00:00Z",
  "bugzilla" : {
    "description" : "kernel: ksm: use range-walk function to jump over holes in scan_get_next_rmap_item",
    "id" : "2422696",
    "url" : "https://bugzilla.redhat.com/show_bug.cgi?id=2422696"
  },
  "cvss3" : {
    "cvss3_base_score" : "5.5",
    "cvss3_scoring_vector" : "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H",
    "status" : "verified"
  },
  "cwe" : "CWE-606",
  "details" : [ "In the Linux kernel, the following vulnerability has been resolved:\nksm: use range-walk function to jump over holes in scan_get_next_rmap_item\nCurrently, scan_get_next_rmap_item() walks every page address in a VMA to\nlocate mergeable pages.  This becomes highly inefficient when scanning\nlarge virtual memory areas that contain mostly unmapped regions, causing\nksmd to use large amount of cpu without deduplicating much pages.\nThis patch replaces the per-address lookup with a range walk using\nwalk_page_range().  The range walker allows KSM to skip over entire\nunmapped holes in a VMA, avoiding unnecessary lookups.  This problem was\npreviously discussed in [1].\nConsider the following test program which creates a 32 TiB mapping in the\nvirtual address space but only populates a single page:\n#include <unistd.h>\n#include <stdio.h>\n#include <sys/mman.h>\n/* 32 TiB */\nconst size_t size = 32ul * 1024 * 1024 * 1024 * 1024;\nint main() {\nchar *area = mmap(NULL, size, PROT_READ | PROT_WRITE,\nMAP_NORESERVE | MAP_PRIVATE | MAP_ANON, -1, 0);\nif (area == MAP_FAILED) {\nperror(\"mmap() failed\\n\");\nreturn -1;\n}\n/* Populate a single page such that we get an anon_vma. */\n*area = 0;\n/* Enable KSM. */\nmadvise(area, size, MADV_MERGEABLE);\npause();\nreturn 0;\n}\n$ ./ksm-sparse  &\n$ echo 1 > /sys/kernel/mm/ksm/run \nWithout this patch ksmd uses 100% of the cpu for a long time (more then 1\nhour in my test machine) scanning all the 32 TiB virtual address space\nthat contain only one mapped page.  This makes ksmd essentially deadlocked\nnot able to deduplicate anything of value.  With this patch ksmd walks\nonly the one mapped page and skips the rest of the 32 TiB virtual address\nspace, making the scan fast using little cpu.", "A resource exhaustion vulnerability was found in the Kernel Same-page Merging (KSM) subsystem of the Linux kernel. When scanning processes with large sparse virtual memory mappings (e.g., 32 TiB with one mapped page), ksmd inefficiently walks every address rather than skipping unmapped holes. This causes ksmd to consume 100% CPU for extended periods." ],
  "statement" : "Any process can create large sparse mappings with MADV_MERGEABLE, causing ksmd to waste CPU cycles. This is a denial of service against the KSM deduplication daemon rather than a memory corruption issue.",
  "affected_release" : [ {
    "product_name" : "Red Hat Enterprise Linux 10",
    "release_date" : "2026-07-31T00:00:00Z",
    "advisory" : "RHSA-2026:49211",
    "cpe" : "cpe:/o:redhat:enterprise_linux:10.2",
    "package" : "kernel-0:6.12.0-211.42.1.el10_2"
  }, {
    "product_name" : "Red Hat Enterprise Linux 9",
    "release_date" : "2026-08-26T00:00:00Z",
    "advisory" : "RHSA-2026:59723",
    "cpe" : "cpe:/a:redhat:enterprise_linux:9",
    "package" : "kernel-0:5.14.0-687.42.1.el9_8"
  }, {
    "product_name" : "Red Hat Enterprise Linux 9",
    "release_date" : "2026-08-26T00:00:00Z",
    "advisory" : "RHSA-2026:59723",
    "cpe" : "cpe:/o:redhat:enterprise_linux:9",
    "package" : "kernel-0:5.14.0-687.42.1.el9_8"
  }, {
    "product_name" : "Red Hat Enterprise Linux 9.6 Extended Update Support",
    "release_date" : "2026-09-02T00:00:00Z",
    "advisory" : "RHSA-2026:62568",
    "cpe" : "cpe:/a:redhat:rhel_eus:9.6",
    "package" : "kernel-0:5.14.0-570.138.1.el9_6"
  } ],
  "package_state" : [ {
    "product_name" : "Red Hat Enterprise Linux 6",
    "fix_state" : "Out of support scope",
    "package_name" : "kernel",
    "cpe" : "cpe:/o:redhat:enterprise_linux:6"
  }, {
    "product_name" : "Red Hat Enterprise Linux 7",
    "fix_state" : "Fix deferred",
    "package_name" : "kernel",
    "cpe" : "cpe:/o:redhat:enterprise_linux:7"
  }, {
    "product_name" : "Red Hat Enterprise Linux 7",
    "fix_state" : "Fix deferred",
    "package_name" : "kernel-rt",
    "cpe" : "cpe:/o:redhat:enterprise_linux:7"
  }, {
    "product_name" : "Red Hat Enterprise Linux 8",
    "fix_state" : "Fix deferred",
    "package_name" : "kernel",
    "cpe" : "cpe:/o:redhat:enterprise_linux:8"
  }, {
    "product_name" : "Red Hat Enterprise Linux 8",
    "fix_state" : "Fix deferred",
    "package_name" : "kernel-rt",
    "cpe" : "cpe:/o:redhat:enterprise_linux:8"
  }, {
    "product_name" : "Red Hat Enterprise Linux 9",
    "fix_state" : "Affected",
    "package_name" : "kernel-rt",
    "cpe" : "cpe:/o:redhat:enterprise_linux:9"
  } ],
  "references" : [ "https://www.cve.org/CVERecord?id=CVE-2025-68211\nhttps://nvd.nist.gov/vuln/detail/CVE-2025-68211\nhttps://lore.kernel.org/linux-cve-announce/2025121634-CVE-2025-68211-180a@gregkh/T" ],
  "name" : "CVE-2025-68211",
  "csaw" : false
}