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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": []
}

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
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)
Linux	Linux	Affected: 7.1 Unaffected: 0 , < 7.1 (semver) Unaffected: 7.2.11 , ≤ 7.2.* (semver) Unaffected: 7.3 , ≤ * (original_commit_for_fix)

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Sightings

Author	Source	Type	Date	Other

Nomenclature

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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.
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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.

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