MediumCVE-2025-68211

    Linux Kernel: Deadlock (CVE-2025-68211)

    Published Last modified Sources: Ubuntu, Red Hat, BSI, Debian, SUSE, CVE.org, Msrc Update Guide, EUVD

    What is affected, what to do

    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.

    Update Linux Kernel to version 5.10.249, Linux Kernel to version 5.15.199, Linux Kernel to version 6.1.161.

    Affected
    • Linux Kernel lt 2.6.32..5.10.249
    • Linux Kernel lt 5.11..5.15.199
    • Linux Kernel lt 5.16..6.1.161
    • Linux Kernel lt 6.2..6.6.121
    • Linux Kernel lt 6.7..6.12.59
    • Linux Kernel lt 6.13..6.17.9
    Fixed in
    • Linux Kernel 5.10.249
    • Linux Kernel 5.15.199
    • Linux Kernel 6.1.161
    • Linux Kernel 6.6.121
    • Linux Kernel 6.12.59
    • Linux Kernel 6.17.9
    • Linux Kernel 6.18

    Not sure whether and how you are affected? Ask a question about this vulnerability

    Metrics

    5.5

    Priority

    XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.

    Source: NVD, CVSS v3

    5.5

    CVSS v3

    Severity Medium on the scale from 0 to 10.

    Source: Ubuntu, Red Hat, BSI, Debian, SUSE, CVE.org, Msrc Update Guide, EUVD

    0.2 %

    EPSS score

    Low — model estimates < 1% exploitation likelihood.

    Source: FIRST EPSS, percentile 3.6

    Show all metrics
    Severity
    Medium
    Priority score

    The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first?

    Read in glossary
    40.63
    Exploit maturity

    An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack.

    Read in glossary
    no public PoC known
    XIEM Effective CVSS

    XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command.

    Read in glossary
    5.5
    CVSS v3

    CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions.

    Read in glossary
    5.5
    EPSS score

    The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“.

    Read in glossary
    0.2 %
    Low — model estimates < 1% exploitation likelihood.
    EPSS percentile

    The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking.

    Read in glossary
    3.6
    Low — this CVE sits in the lower 10% of all CVEs scored today.
    KEV status

    The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.

    Read in glossary
    —
    Published

    Classification under NIS2 and CRA

    Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.

    NIS2

    NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management.

    Read in glossary
    Handle the vulnerability in regular vulnerability handling under Art. 21(2)(e) NIS2.
    CRA

    The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates.

    Read in glossary
    From 11.12.2027, Annex I Part II CRA requires manufacturers of affected products with digital elements to handle vulnerabilities without delay and provide security updates.
    ISO/IEC 27001

    ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security.

    Read in glossary
    Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.

    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.

    Source: Ubuntu Security Notices, redhat_csaf, BSI WID Portal, BSI CSAF, Debian Security Advisories, suse_csaf, NVD (NIST), Microsoft Security Update Guide, CVE.org (MITRE), cvelistv5, ENISA EUVD

    Affected products

    The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.

    Affected products
    VendorProductAffected versionsFixed in
    LinuxLinux
    • 2.6.32 – < 5.10.249
    • 5.11 – < 5.15.199
    • 5.16 – < 6.1.161
    • 6.13 – < 6.17.9
    • 6.2 – < 6.6.121
    • 6.7 – < 6.12.59
    • —
    • 5.10.249
    • 5.15.199
    • 6.1.161
    • 6.17.9
    • 6.6.121
    • 6.12.59
    • 6.18
    IBMDataPower Gateway
    • < 10.5.0.23
    • < 10.6.0.11
    • < 11.0.0.3
    • 10.5.0.23
    • 10.6.0.11
    • 11.0.0.3

    Affected operating systems

    Affected operating systems
    FamilyVendorProductVersion
    Linuxlinuxlinux_kernel6.18
    Linuxlinuxlinux_kernel—

    References & sources

    Reanalysis & status changes

    Chronological NVD audit events for this CVE — reanalyses, CVSS updates, CPE diffs.

    1. CVE Translatednvd@nist.gov

      • Translation: after Title: Linux, Description: En el kernel de Linux, la siguiente vulnerabilidad ha sido resuelta: ksm: usar la función de recorrido de rango para saltar sobre los huecos en scan_get_next_rmap_item Actualmente, scan_get_next_rmap_item() recorre cada dirección de página en un VMA para localizar páginas fusionables. Esto se vuelve altamente ineficiente al escanear grandes áreas de memoria virtual que contienen en su mayoría regiones no mapeadas, lo que hace que ksmd use una gran cantidad de CPU sin desduplicar muchas páginas. Este parche reemplaza la búsqueda por dirección con un recorrido de rango usando walk_page_range(). El recorredor de rangos permite a KSM saltar sobre huecos no mapeados completos en un VMA, evitando búsquedas innecesarias. Este problema fue discutido previamente en [1]. Considere el siguiente programa de prueba que crea un mapeo de 32 TiB en el espacio de direcciones virtual pero solo rellena una única página: #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 Sin este parche, ksmd usa el 100% de la CPU durante mucho tiempo (más de 1 hora en mi máquina de prueba) escaneando todo el espacio de direcciones virtual de 32 TiB que contiene solo una página mapeada. Esto hace que ksmd quede esencialmente bloqueado sin poder desduplicar nada de valor. Con este parche, ksmd recorre solo la página mapeada y salta el resto del espacio de direcciones virtual de 32 TiB, haciendo que el escaneo sea rápido usando poca CPU.