Vulnerability-Lookup

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

Vulnerability from cvelistv5 – Published: 2026-10-23 12:20 – Updated: 2026-10-23 12:20

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 7061 records in the last 180 days details

References

2 references

URL	Tags
https://git.kernel.org/stable/c/56fe03a0c05dba4c5…
https://git.kernel.org/stable/c/0b6f31a3c0b16066f…

Impacted products

2 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
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

Show details on NVD website

JSON

To clipboard

{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "include/linux/nsproxy.h",
            "kernel/fork.c",
            "kernel/nsproxy.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
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              "version": "a98621a0f187a934c115dcfe79a49520ae892111",
              "versionType": "git"
            },
            {
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              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "27ae6b17c9ba7ff353ab0906297f08aa845782b4",
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            },
            {
              "status": "affected",
              "version": "297261b343371c4f0b31055d53d285138ec21565",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "813a47b0309097da71781ee4ac11922e39b67d55",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "6e608e3e5ce12ce7fd21e46212eccca37f917d0e",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "a261fccdb4ac58ec5ba6aa1d92a6cc418fff301f",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "665dc1ed16357988d439fc5bbc860ee36f540d81",
              "versionType": "git"
            },
            {
              "lessThan": "5.16",
              "status": "affected",
              "version": "5.15.209",
              "versionType": "semver"
            },
            {
              "lessThan": "6.2",
              "status": "affected",
              "version": "6.1.175",
              "versionType": "semver"
            },
            {
              "lessThan": "6.7",
              "status": "affected",
              "version": "6.6.141",
              "versionType": "semver"
            },
            {
              "lessThan": "6.13",
              "status": "affected",
              "version": "6.12.91",
              "versionType": "semver"
            },
            {
              "lessThan": "6.19",
              "status": "affected",
              "version": "6.18.33",
              "versionType": "semver"
            },
            {
              "lessThan": "7.1",
              "status": "affected",
              "version": "7.0.10",
              "versionType": "semver"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "include/linux/nsproxy.h",
            "kernel/fork.c",
            "kernel/nsproxy.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "7.1"
            },
            {
              "lessThan": "7.1",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.2.*",
              "status": "unaffected",
              "version": "7.2.11",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.3",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.2.11",
                  "versionStartIncluding": "7.1",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.3",
                  "versionStartIncluding": "7.1",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionStartIncluding": "5.15.209",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionStartIncluding": "6.1.175",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionStartIncluding": "6.6.141",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionStartIncluding": "6.12.91",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionStartIncluding": "6.18.33",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionStartIncluding": "7.0.10",
                  "vulnerable": true
                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "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."
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-23T12:20:00.918Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/56fe03a0c05dba4c5f6a23c391f96de1614a098c"
        },
        {
          "url": "https://git.kernel.org/stable/c/0b6f31a3c0b16066f812e94b52a704174a6f23cd"
        }
      ],
      "title": "unshare: don\u0027t drop active namespace references that were never taken",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-98983",
    "datePublished": "2026-10-23T12:20:00.918Z",
    "dateReserved": "2026-09-25T10:25:14.384Z",
    "dateUpdated": "2026-10-23T12:20:00.918Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
    "nvd": {
      "cve": {
        "affected": [
          {
            "affectedData": [
              {
                "defaultStatus": "unaffected",
                "product": "Linux",
                "programFiles": [
                  "include/linux/nsproxy.h",
                  "kernel/fork.c",
                  "kernel/nsproxy.c"
                ],
                "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
                "vendor": "Linux",
                "versions": [
                  {
                    "lessThan": "56fe03a0c05dba4c5f6a23c391f96de1614a098c",
                    "status": "affected",
                    "version": "a98621a0f187a934c115dcfe79a49520ae892111",
                    "versionType": "git"
                  },
                  {
                    "lessThan": "0b6f31a3c0b16066f812e94b52a704174a6f23cd",
                    "status": "affected",
                    "version": "a98621a0f187a934c115dcfe79a49520ae892111",
                    "versionType": "git"
                  },
                  {
                    "status": "affected",
                    "version": "27ae6b17c9ba7ff353ab0906297f08aa845782b4",
                    "versionType": "git"
                  },
                  {
                    "status": "affected",
                    "version": "297261b343371c4f0b31055d53d285138ec21565",
                    "versionType": "git"
                  },
                  {
                    "status": "affected",
                    "version": "813a47b0309097da71781ee4ac11922e39b67d55",
                    "versionType": "git"
                  },
                  {
                    "status": "affected",
                    "version": "6e608e3e5ce12ce7fd21e46212eccca37f917d0e",
                    "versionType": "git"
                  },
                  {
                    "status": "affected",
                    "version": "a261fccdb4ac58ec5ba6aa1d92a6cc418fff301f",
                    "versionType": "git"
                  },
                  {
                    "status": "affected",
                    "version": "665dc1ed16357988d439fc5bbc860ee36f540d81",
                    "versionType": "git"
                  },
                  {
                    "lessThan": "5.16",
                    "status": "affected",
                    "version": "5.15.209",
                    "versionType": "semver"
                  },
                  {
                    "lessThan": "6.2",
                    "status": "affected",
                    "version": "6.1.175",
                    "versionType": "semver"
                  },
                  {
                    "lessThan": "6.7",
                    "status": "affected",
                    "version": "6.6.141",
                    "versionType": "semver"
                  },
                  {
                    "lessThan": "6.13",
                    "status": "affected",
                    "version": "6.12.91",
                    "versionType": "semver"
                  },
                  {
                    "lessThan": "6.19",
                    "status": "affected",
                    "version": "6.18.33",
                    "versionType": "semver"
                  },
                  {
                    "lessThan": "7.1",
                    "status": "affected",
                    "version": "7.0.10",
                    "versionType": "semver"
                  }
                ]
              },
              {
                "defaultStatus": "affected",
                "product": "Linux",
                "programFiles": [
                  "include/linux/nsproxy.h",
                  "kernel/fork.c",
                  "kernel/nsproxy.c"
                ],
                "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
                "vendor": "Linux",
                "versions": [
                  {
                    "status": "affected",
                    "version": "7.1"
                  },
                  {
                    "lessThan": "7.1",
                    "status": "unaffected",
                    "version": "0",
                    "versionType": "semver"
                  },
                  {
                    "lessThanOrEqual": "7.2.*",
                    "status": "unaffected",
                    "version": "7.2.11",
                    "versionType": "semver"
                  },
                  {
                    "lessThanOrEqual": "*",
                    "status": "unaffected",
                    "version": "7.3",
                    "versionType": "original_commit_for_fix"
                  }
                ]
              }
            ],
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
          }
        ],
        "cveTags": [],
        "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",
            "url": "https://git.kernel.org/stable/c/0b6f31a3c0b16066f812e94b52a704174a6f23cd"
          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/56fe03a0c05dba4c5f6a23c391f96de1614a098c"
          }
        ],
        "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "vulnStatus": "Received"
      }
    }
  }
}

FKIE_CVE-2026-98983

Vulnerability from fkie_nvd - Published: 2026-10-23 13:17 - Updated: 2026-10-23 13:17

Severity

Summary

References

	URL	Tags
	416baaa9-dc9f-4396-8d5f-8c081fb06d67	https://git.kernel.org/stable/c/0b6f31a3c0b16066f812e94b52a704174a6f23cd
	416baaa9-dc9f-4396-8d5f-8c081fb06d67	https://git.kernel.org/stable/c/56fe03a0c05dba4c5f6a23c391f96de1614a098c

Impacted products

	Vendor	Product	Version

JSON

To clipboard

{
  "affected": [
    {
      "affectedData": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "include/linux/nsproxy.h",
            "kernel/fork.c",
            "kernel/nsproxy.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "56fe03a0c05dba4c5f6a23c391f96de1614a098c",
              "status": "affected",
              "version": "a98621a0f187a934c115dcfe79a49520ae892111",
              "versionType": "git"
            },
            {
              "lessThan": "0b6f31a3c0b16066f812e94b52a704174a6f23cd",
              "status": "affected",
              "version": "a98621a0f187a934c115dcfe79a49520ae892111",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "27ae6b17c9ba7ff353ab0906297f08aa845782b4",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "297261b343371c4f0b31055d53d285138ec21565",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "813a47b0309097da71781ee4ac11922e39b67d55",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "6e608e3e5ce12ce7fd21e46212eccca37f917d0e",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "a261fccdb4ac58ec5ba6aa1d92a6cc418fff301f",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "665dc1ed16357988d439fc5bbc860ee36f540d81",
              "versionType": "git"
            },
            {
              "lessThan": "5.16",
              "status": "affected",
              "version": "5.15.209",
              "versionType": "semver"
            },
            {
              "lessThan": "6.2",
              "status": "affected",
              "version": "6.1.175",
              "versionType": "semver"
            },
            {
              "lessThan": "6.7",
              "status": "affected",
              "version": "6.6.141",
              "versionType": "semver"
            },
            {
              "lessThan": "6.13",
              "status": "affected",
              "version": "6.12.91",
              "versionType": "semver"
            },
            {
              "lessThan": "6.19",
              "status": "affected",
              "version": "6.18.33",
              "versionType": "semver"
            },
            {
              "lessThan": "7.1",
              "status": "affected",
              "version": "7.0.10",
              "versionType": "semver"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "include/linux/nsproxy.h",
            "kernel/fork.c",
            "kernel/nsproxy.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "7.1"
            },
            {
              "lessThan": "7.1",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.2.*",
              "status": "unaffected",
              "version": "7.2.11",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.3",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    }
  ],
  "cveTags": [],
  "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",
      "url": "https://git.kernel.org/stable/c/0b6f31a3c0b16066f812e94b52a704174a6f23cd"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/56fe03a0c05dba4c5f6a23c391f96de1614a098c"
    }
  ],
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "vulnStatus": "Received"
}

GHSA-VC4V-Q632-X9G5

Vulnerability from github – Published: 2026-10-23 15:31 – Updated: 2026-10-23 15:31

Details

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.

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{
  "affected": [],
  "aliases": [
    "CVE-2026-98983"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-10-23T13:17:20Z",
    "severity": null
  },
  "details": "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": "GHSA-vc4v-q632-x9g5",
  "modified": "2026-10-23T15:31:33Z",
  "published": "2026-10-23T15:31:33Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-98983"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/0b6f31a3c0b16066f812e94b52a704174a6f23cd"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/56fe03a0c05dba4c5f6a23c391f96de1614a098c"
    }
  ],
  "schema_version": "1.4.0",
  "severity": []
}

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

FKIE_CVE-2026-98983

GHSA-VC4V-Q632-X9G5

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