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CVE.org (no NVD analysis yet)· CNA Linux

CVE-2026-98983: unshare: don't drop active namespace references that were never taken

Noroxi assessment

Priority: Monitor (action score 0/100)

  • The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
  • Probability of exploitation in the next 30 days: 0.16% (FIRST EPSS).
  • Fixed version: Linux Linux 0b6f31a3c0b16066f812e94b52a704174a6f23cd, 5.16, 56fe03a0c05dba4c5f6a23c391f96de1614a098c.
  • Mentioned 1 time in Turkish national cyber security advisories (siberguvenlik.gov.tr).

Low priority for now. Upgrade to Linux Linux 0b6f31a3c0b16066f812e94b52a704174a6f23cd, 5.16, 56fe03a0c05dba4c5f6a23c391f96de1614a098c or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

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.

—No exploit Fix available
Published
Oct 23, 2026
Updated
Oct 23, 2026
EPSS
0.1% · 5th percentile
CWE
—

Report tools

JSON

Action score

0

Monitor

Low priority for now.

CVSS
0 / 40 · —
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.1%

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Noroxi analysis

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

—

Versions reported by the vendor

Affected version ranges reported by the assigning authority (Linux). Independent of NVD's CPE analysis and usually ahead of it.

  • Linux Linux

    • 27ae6b17c9ba7ff353ab0906297f08aa845782b4, 297261b343371c4f0b31055d53d285138ec21565, 813a47b0309097da71781ee4ac11922e39b67d55, 6e608e3e5ce12ce7fd21e46212eccca37f917d0e, a261fccdb4ac58ec5ba6aa1d92a6cc418fff301f, 665dc1ed16357988d439fc5bbc860ee36f540d81, 7.1affected
    • a98621a0f187a934c115dcfe79a49520ae892111 and later · before 56fe03a0c05dba4c5f6a23c391f96de1614a098caffected · git
    • a98621a0f187a934c115dcfe79a49520ae892111 and later · before 0b6f31a3c0b16066f812e94b52a704174a6f23cdaffected · git
    • 5.15.209 and later · before 5.16affected · semver
    • 6.1.175 and later · before 6.2affected · semver
    • 6.6.141 and later · before 6.7affected · semver
    • 6.12.91 and later · before 6.13affected · semver
    • 6.18.33 and later · before 6.19affected · semver
    • 7.0.10 and later · before 7.1affected · semver
    • before 7.1not affected · semver

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
Debian:12linuxfrom 0—
Debian:14linuxbefore 7.2.11-17.2.11-1

Same product

linux: all records

Other highest-scoring records for the same primary product.

  • CVE-2026-74705udp: fix potential use-after-free in tunnel segmentation
    40Plan
  • CVE-2026-74612veth: fix skb length accounting after XDP frag adjustment
    40Plan
  • CVE-2026-74475vxlan: use neigh_ha_snapshot() in route_shortcircuit()
    40Plan

Published before and after this one in the same product

  • ← EarlierCVE-2026-98981Oct 23, 2026 · namespace: unhash a dentry before detaching the mounts on it
    35Monitor
  • ← EarlierCVE-2026-98982Oct 23, 2026 · namespace: don't let a pseudo dentry become the root of a mount
    31Monitor
  • Later →CVE-2026-98984Oct 23, 2026 · dcache: don't put a mountpoint on a dentry that's being removed
    0Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
Linux Linux0b6f31a3c0b16066f812e94b52a704174a6f23cdVendor (CNA)
Linux Linux5.16Vendor (CNA)
Linux Linux56fe03a0c05dba4c5f6a23c391f96de1614a098cVendor (CNA)
Linux Linux6.13Vendor (CNA)
Linux Linux6.19Vendor (CNA)
Linux Linux6.2Vendor (CNA)
Linux Linux6.7Vendor (CNA)
Linux Linux7.1Vendor (CNA)
debian:linux7.2.11-1 · Debian:14Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

  1. Published
  2. Fix recordedsame day
  3. TodayNov 4, 2026+11 d
EPSS, last 120 days

FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

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No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

No nightly-computed relations.

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

National notice (Türkiye Cybersecurity Directorate / USOM)

Official security notices citing this record; remediation advice is on the agency's page.

All national notices →

Technical details

No CVSS vector for this record, so attack conditions can't be derived.

Weakness class (CWE)

—

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

MITRE has no CAPEC/ATT&CK mapping for this CWE.

Change log

  1. Exploit maturity— → none
  2. Fix✗ → ✓

For records you follow, these changes also arrive as notifications. →

References

Show all references (1 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

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