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CVE-2026-89593 (GCVE-0-2026-89593)

Vulnerability from cvelistv5 – Published: 2026-09-11 19:44 – Updated: 2026-09-14 12:01
VLAI
Title
hugetlb: only adjust reservation during unmapping if mapcount is 0
Summary
In the Linux kernel, the following vulnerability has been resolved: hugetlb: only adjust reservation during unmapping if mapcount is 0 Since df7a6d1f6405, __unmap_hugepage_range can adjust reservations. In the case of folio mapped in both a parent and a child, if the parent unmaps the range first, the reservation adjustment will result in an underflow of the reserved count. Once the child unmaps the range, the count is restored. Change __unmap_hugepage_range() to check the mapcount before adjusting the reservation.
Severity
7.1 (High)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:H
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: df7a6d1f64056aec572162c5d35ed9ff86ece6f3 , < b0b1b9ca80b795ed2223e76dd787db7067121fb9 (git)
Affected: df7a6d1f64056aec572162c5d35ed9ff86ece6f3 , < a3c65af20cceb7f997847727636b4017326f845d (git)
Affected: df7a6d1f64056aec572162c5d35ed9ff86ece6f3 , < 0f001491e5a2ec69aa9d5dd6b799e5742245f9ea (git)
Affected: df7a6d1f64056aec572162c5d35ed9ff86ece6f3 , < 5120b1e048d48596ffaec1a8412012a91adba73b (git)
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Linux Linux Affected: 6.9
Unaffected: 0 , < 6.9 (semver)
Unaffected: 6.12.110 , ≤ 6.12.* (semver)
Unaffected: 6.18.50 , ≤ 6.18.* (semver)
Unaffected: 7.2.4 , ≤ 7.2.* (semver)
Unaffected: 7.3-rc1 , ≤ * (original_commit_for_fix)
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{
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          "product": "Linux",
          "programFiles": [
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          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nhugetlb: only adjust reservation during unmapping if mapcount is 0\n\nSince df7a6d1f6405, __unmap_hugepage_range can adjust reservations.  In\nthe case of folio mapped in both a parent and a child, if the parent\nunmaps the range first, the reservation adjustment will result in an\nunderflow of the reserved count.  Once the child unmaps the range, the\ncount is restored.  Change __unmap_hugepage_range() to check the mapcount\nbefore adjusting the reservation."
        }
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              "value": "AV:L - The bug is in __unmap_hugepage_range() on munmap/madvise of a private MAP_HUGETLB VMA after fork, reached only via local mmap/fault/fork/unmap syscalls, not from any network protocol or remote packet path.\nAC:L - Triggering is a deterministic sequence: MAP_PRIVATE|MAP_ANONYMOUS|MAP_HUGETLB mmap, fault the page, fork, then munmap in the parent while the child keeps the mapping. The reporter\u0027s reproducer underflows HugePages_Rsvd on every run with no race.\nPR:L - mmap(MAP_ANONYMOUS|MAP_HUGETLB) uses hugetlb_file_setup(HUGETLB_ANONHUGE_INODE) with no CAP_IPC_LOCK check. An unprivileged local user on a host with hugepages (typical for VMs, databases, DPDK, and HPC) can exercise this path, including from a user namespace.\nUI:N - The attacker creates the private hugetlb mapping, forks, and unmaps in their own processes; no action by another user or administrator is required.\nS:U - Impact is corruption of the host kernel\u0027s global hugetlb reservation counter (h-\u003eresv_huge_pages) within the same kernel security domain; it does not escape a VM, bypass an IOMMU, or cross another authority.\nC:N - The flaw only underflows and wraps the hugepage reservation counter; it does not provide an out-of-bounds read, use-after-free, or other primitive that discloses kernel memory or confidential data.\nI:H - Parent unmap while a child still maps the folio restores the reserve map, then hugetlb_vm_op_close() decrements resv_huge_pages from zero and wraps it to ULONG_MAX, corrupting global reservation accounting so later allocations can steal hugepages reserved for other tenants and bypass reservation guarantees.\nA:H - With resv_huge_pages wrapped, available_huge_pages() and gather_surplus_pages() treat the pool as having extra pages, so other hugepage users (QEMU, databases, DPDK) can be denied reserved pages and SIGBUS. The attacker controls the child lifetime, so broken accounting can persist and remain desynchronized."
            }
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      "providerMetadata": {
        "dateUpdated": "2026-09-14T12:01:16.035Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
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    "cveId": "CVE-2026-89593",
    "datePublished": "2026-09-11T19:44:56.557Z",
    "dateReserved": "2026-09-11T19:38:34.730Z",
    "dateUpdated": "2026-09-14T12:01:16.035Z",
    "state": "PUBLISHED"
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    "redhat_vex": {
      "aggregate_severity": "Low",
      "current_release_date": "2026-09-14T10:01:20+00:00",
      "cve": "CVE-2026-89593",
      "id": "CVE-2026-89593",
      "initial_release_date": "2026-09-11T00:00:00+00:00",
      "product_status:known_affected": "199",
      "product_status:known_not_affected": "77",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: hugetlb: only adjust reservation during unmapping if mapcount is 0",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89593.json",
      "version": "3"
    },
    "suse_vex": {
      "aggregate_severity": "moderate",
      "current_release_date": "2026-09-15T00:58:05Z",
      "cve": "CVE-2026-89593",
      "id": "CVE-2026-89593",
      "initial_release_date": "2026-09-12T16:25:30Z",
      "product_status:known_affected": "17",
      "product_status:known_not_affected": "336",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2026-89593",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2026-89593.json",
      "version": "4"
    }
  }
}



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Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

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Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.


Detection rules are retrieved from Rulezet.