CVE-2025-68211: Linux kernel · ksm: use range-walk function to jump over holes in scan_get_next_rmap_item
Affects Linux kernelSource GCVE Database
Not known to be exploited · CVSS 5.5 Medium · fixed in 5.15.0-1105.112~20.04.1 : update Linux kernel when convenient.
Data as of 26 Oct 2026, 17:16 UTC
- EPSS
- 0.1% chance of exploitation in 30 days – higher than 3% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
- Patch
- Available – fixed in 5.15.0-1105.112~20.04.1, 5.15.0-1110.119~20.04.1, 5.15.0-1106.115~20.04.1 +39
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:HExploitation evidence
Disclosed: evidence found.
CVE published 16 Dec 2025
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors
A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.
What to do
Upgrade to a fixed release listed under Affected software.
Patches and advisories
- ubuntu.com/security/notices/USN-8029-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-8030-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-8029-2 (opens in a new tab)
- ubuntu.com/security/notices/USN-8048-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-8029-3 (opens in a new tab)
- ubuntu.com/security/notices/USN-8162-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-8180-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-8180-2 (opens in a new tab)
- ubuntu.com/security/notices/USN-8186-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-8187-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-8188-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-8180-3 (opens in a new tab)
Affected software
| Product | Affected | Fixed in |
|---|---|---|
Ubuntu 25.10linuxpkg:deb/ubuntu/linux?arch=source&distro=questingOther threats | Affected
| Fixed in
|
Ubuntu 25.10linux-awspkg:deb/ubuntu/linux-aws?arch=source&distro=questingOther threats | Affected
| Fixed in
|
Ubuntu 25.10linux-azurepkg:deb/ubuntu/linux-azure?arch=source&distro=questingOther threats | Affected
| Fixed in
|
Ubuntu 25.10linux-azure-fdepkg:deb/ubuntu/linux-azure-fde?arch=source&distro=questingOther threats | Affected
| Fixed in– |
Ubuntu 25.10linux-gcppkg:deb/ubuntu/linux-gcp?arch=source&distro=questingOther threats | Affected
| Fixed in
|
Ubuntu 25.10linux-oraclepkg:deb/ubuntu/linux-oracle?arch=source&distro=questingOther threats | Affected
| Fixed in
|
Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.
Description
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.
References
- ubuntu.com/security/CVE-2025-68211 (opens in a new tab)
- cve.org/CVERecord?id=CVE-2025-68211 (opens in a new tab)
- git.kernel.org/linus/f5548c318d6520d4fa3c5ed6003eeb710763cbc5 (opens in a new tab)
- git.kernel.org/stable/c/74f78421c925b6d17695566f0c5941de57fd44b3 (opens in a new tab)
- git.kernel.org/stable/c/f5548c318d6520d4fa3c5ed6003eeb710763cbc5 (opens in a new tab)
- git.kernel.org/stable/c/f62973e0767e4fcd6799087787fca08ca2a85b8c (opens in a new tab)
- ubuntu.com/security/notices/USN-8029-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-8030-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-8029-2 (opens in a new tab)
- ubuntu.com/security/notices/USN-8048-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-8029-3 (opens in a new tab)
- ubuntu.com/security/notices/USN-8162-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-8180-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-8180-2 (opens in a new tab)
- ubuntu.com/security/notices/USN-8186-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-8187-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-8188-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-8180-3 (opens in a new tab)
- ubuntu.com/security/notices/USN-8180-4 (opens in a new tab)
- ubuntu.com/security/notices/USN-8180-5 (opens in a new tab)