CVE-2026-98983: Linux Vulnerability

Description

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.

Affected Software

Source: CNA advisory (CVE.org). NVD analysis pending.

Vendor	Product	Versions
Linux	Linux	>= a98621a0f187a934c115dcfe79a49520ae892111, < 56fe03a0c05dba4c5f6a23c391f96de1614a098c; >= a98621a0f187a934c115dcfe79a49520ae892111, < 0b6f31a3c0b16066f812e94b52a704174a6f23cd; 27ae6b17c9ba7ff353ab0906297f08aa845782b4; 297261b343371c4f0b31055d53d285138ec21565; 813a47b0309097da71781ee4ac11922e39b67d55; 6e608e3e5ce12ce7fd21e46212eccca37f917d0e; a261fccdb4ac58ec5ba6aa1d92a6cc418fff301f; 665dc1ed16357988d439fc5bbc860ee36f540d81; >= 5.15.209, < 5.16; >= 6.1.175, < 6.2; >= 6.6.141, < 6.7; >= 6.12.91, < 6.13; >= 6.18.33, < 6.19; >= 7.0.10, < 7.1
Linux	Linux	7.1

References

Timeline

Published: Oct 23, 2026
Last Modified: Oct 23, 2026
Status: Received

Frequently Asked Questions

What is CVE-2026-98983?

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.

How severe is CVE-2026-98983?

Severity scoring for CVE-2026-98983 is pending analysis.

How do I fix CVE-2026-98983?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

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