Skip to content
Fencer Intel
no cvss —

CVE-2026-98983 json

unshare: don't drop active namespace references that were never taken

published 19d ago modified 19d ago also EUVD-2026-108777

cvss
—
not scored
cisa kev
Not listed
not in CISA's catalog
epss
0.2%
EPSS 0.2% chance of exploitation in 30 days, percentile 5%
public exploits
0
none known

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.

Patch / fix

  • Linux Linux 5.16, 6.2, 6.7, 6.13, 6.19, 7.1, 7.3
  • linux Debian 14 7.2.11-1

debian advisories DEBIAN-CVE-2026-98983

  • linux Ubuntu 26.10 7.3.0-10.10
  • linux-aws Ubuntu 26.10 7.3.0-1004.4
  • linux-gcp Ubuntu 26.10 7.3.0-1004.4
  • linux-raspi Ubuntu 26.10 7.3.0-1004.4
  • linux-riscv Ubuntu 26.10 7.3.0-10.10.1
  • linux-oracle Ubuntu 26.10 7.3.0-1004.4
  • linux-realtime Ubuntu 26.10 7.3.0-10.10.1

ubuntu advisories UBUNTU-CVE-2026-98983

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

Is CVE-2026-98983 in your stack? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.

Check with Fencer

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-98983 updated cvss 4.7

kernel: unshare: don't drop active namespace references that were never taken

  • Red Hat Enterprise Linux 6 perf, kernel, python-perf, kernel-kdump, kernel-firmware, kernel-bootwrapper, +1 more
    affected: no fix planned “Out of support scope”
  • Red Hat Enterprise Linux 7 perf, kernel, bpftool, kernel-rt, python-perf, kernel-kdump, +8 more Red Hat Enterprise Linux 8 perf, kernel, bpftool, kernel-rt, kernel-core, kernel-tools, +29 more Red Hat Enterprise Linux 9 rv, perf, rtla, kernel, bpftool, libperf, +83 more Red Hat Enterprise Linux 10 kernel Red Hat OpenShift Container Platform 4 openshift/ose-rhel-coreos-8, openshift/ose-rhel-coreos-9 Red Hat OpenShift Container Platform 5 openshift/ose-rhel-coreos-9
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

0.16% chance of exploitation in the next 30 days, higher than 5% of all scored CVEs (FIRST EPSS, 2026-11-11).

Affected products

  • Linux Linux

Classification

Technology feeds

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.