CVE-2026-98983 (GCVE-0-2026-98983)

Vulnerability from cvelistv5 – Published: 2026-10-23 12:20 – Updated: 2026-10-23 12:20
VLAI
Title
unshare: don't drop active namespace references that were never taken
Summary
In the Linux kernel, the following vulnerability has been resolved: unshare: don't drop active namespace references that were never taken Active references on the namespaces of an nsproxy are taken when the nsproxy is installed into a task in switch_task_namespaces() and copy_namespaces() and dropped again by put_nsproxy() through deactivate_nsproxy(). But ksys_unshare() calls put_nsproxy() on an nsproxy that was never installed when set_cred_ucounts() fails. The new namespaces of that nsproxy go from zero to minus one and the namespaces shared with the caller lose a reference that belongs to the nsproxy the caller keeps using: WARNING: kernel/nscommon.c:171 at __ns_ref_active_put+0x1cd/0x230 nsproxy_ns_active_put deactivate_nsproxy ksys_unshare Afterwards the namespaces the caller lives in aren't listed by listns() anymore. set_cred_ucounts() only fails when alloc_ucounts() can't allocate and it only allocates when the real uid of the caller differs from its effective uid. Commit cefd55bd2159 ("nsproxy: fix free_nsproxy() and simplify create_new_namespaces()") separated the two cases on purpose. nsproxy_free() frees an nsproxy that was prepared but never installed and that's what a failed setns() uses in put_nsset(). Export it and use it for a failed unshare() as well.
Severity
No CVSS data available.
Assigner
Linux CNA under the mitre root
CNA scorecard D 53/100 over 6653 records in the last 180 days details
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: a98621a0f187a934c115dcfe79a49520ae892111 , < 56fe03a0c05dba4c5f6a23c391f96de1614a098c (git)
Affected: a98621a0f187a934c115dcfe79a49520ae892111 , < 0b6f31a3c0b16066f812e94b52a704174a6f23cd (git)
Affected: 27ae6b17c9ba7ff353ab0906297f08aa845782b4 (git)
Affected: 297261b343371c4f0b31055d53d285138ec21565 (git)
Affected: 813a47b0309097da71781ee4ac11922e39b67d55 (git)
Affected: 6e608e3e5ce12ce7fd21e46212eccca37f917d0e (git)
Affected: a261fccdb4ac58ec5ba6aa1d92a6cc418fff301f (git)
Affected: 665dc1ed16357988d439fc5bbc860ee36f540d81 (git)
Affected: 5.15.209 , < 5.16 (semver)
Affected: 6.1.175 , < 6.2 (semver)
Affected: 6.6.141 , < 6.7 (semver)
Affected: 6.12.91 , < 6.13 (semver)
Affected: 6.18.33 , < 6.19 (semver)
Affected: 7.0.10 , < 7.1 (semver)
guessed Create a notification for this product.
Linux Linux Affected: 7.1
Unaffected: 0 , < 7.1 (semver)
Unaffected: 7.2.11 , ≤ 7.2.* (semver)
Unaffected: 7.3 , ≤ * (original_commit_for_fix)
guessed Create a notification for this product.
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          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nunshare: don\u0027t drop active namespace references that were never taken\n\nActive references on the namespaces of an nsproxy are taken when the\nnsproxy is installed into a task in switch_task_namespaces() and\ncopy_namespaces() and dropped again by put_nsproxy() through\ndeactivate_nsproxy().\n\nBut ksys_unshare() calls put_nsproxy() on an nsproxy that was never\ninstalled when set_cred_ucounts() fails. The new namespaces of that\nnsproxy go from zero to minus one and the namespaces shared with the\ncaller lose a reference that belongs to the nsproxy the caller keeps\nusing:\n\n  WARNING: kernel/nscommon.c:171 at __ns_ref_active_put+0x1cd/0x230\n   nsproxy_ns_active_put\n   deactivate_nsproxy\n   ksys_unshare\n\nAfterwards the namespaces the caller lives in aren\u0027t listed by listns()\nanymore. set_cred_ucounts() only fails when alloc_ucounts() can\u0027t\nallocate and it only allocates when the real uid of the caller differs\nfrom its effective uid.\n\nCommit cefd55bd2159 (\"nsproxy: fix free_nsproxy() and simplify\ncreate_new_namespaces()\") separated the two cases on purpose.\nnsproxy_free() frees an nsproxy that was prepared but never installed\nand that\u0027s what a failed setns() uses in put_nsset(). Export it and use\nit for a failed unshare() as well."
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-23T12:20:00.918Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
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    "dateReserved": "2026-09-25T10:25:14.384Z",
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    "state": "PUBLISHED"
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        "descriptions": [
          {
            "lang": "en",
            "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nunshare: don\u0027t drop active namespace references that were never taken\n\nActive references on the namespaces of an nsproxy are taken when the\nnsproxy is installed into a task in switch_task_namespaces() and\ncopy_namespaces() and dropped again by put_nsproxy() through\ndeactivate_nsproxy().\n\nBut ksys_unshare() calls put_nsproxy() on an nsproxy that was never\ninstalled when set_cred_ucounts() fails. The new namespaces of that\nnsproxy go from zero to minus one and the namespaces shared with the\ncaller lose a reference that belongs to the nsproxy the caller keeps\nusing:\n\n  WARNING: kernel/nscommon.c:171 at __ns_ref_active_put+0x1cd/0x230\n   nsproxy_ns_active_put\n   deactivate_nsproxy\n   ksys_unshare\n\nAfterwards the namespaces the caller lives in aren\u0027t listed by listns()\nanymore. set_cred_ucounts() only fails when alloc_ucounts() can\u0027t\nallocate and it only allocates when the real uid of the caller differs\nfrom its effective uid.\n\nCommit cefd55bd2159 (\"nsproxy: fix free_nsproxy() and simplify\ncreate_new_namespaces()\") separated the two cases on purpose.\nnsproxy_free() frees an nsproxy that was prepared but never installed\nand that\u0027s what a failed setns() uses in put_nsset(). Export it and use\nit for a failed unshare() as well."
          }
        ],
        "id": "CVE-2026-98983",
        "lastModified": "2026-10-23T13:17:20.160",
        "metrics": {},
        "published": "2026-10-23T13:17:20.160",
        "references": [
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
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        "vulnStatus": "Received"
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      "current_release_date": "2026-11-06T03:20:08+00:00",
      "cve": "CVE-2026-98983",
      "id": "CVE-2026-98983",
      "initial_release_date": "2026-10-23T00:00:00+00:00",
      "product_status:known_affected": "14",
      "product_status:known_not_affected": "189",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: unshare: don\u0027t drop active namespace references that were never taken",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-98983.json",
      "version": "3"
    },
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      "aggregate_severity": "moderate",
      "current_release_date": "2026-11-04T17:47:10Z",
      "cve": "CVE-2026-98983",
      "id": "CVE-2026-98983",
      "initial_release_date": "2026-10-27T00:42:00Z",
      "product_status:known_not_affected": "348",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2026-98983",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/2026/cve-2026-98983.json",
      "version": "3"
    }
  }
}



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