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

Quick assessment

Affected

Linux Linux

Exploitation

No confirmed in-the-wild exploitation; assess based on exposure

Recommended action

Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

在 Linux 内核中，以下漏洞已得到修复： unshare：不要丢弃那些从未被引用的活跃命名空间引用当通过或安装到某个任务时，会获取该所关联命名空间的活跃引用；随后，这些引用会通过调用再次释放。然而，当失败时，会直接对一个从未被安装的调用。这导致该的新命名空间引用计数从 0 变为 -1，而调用者所共享的命名空间则丢失了本应由该持有的引用（调用者仍在继续使用它）：此后，调用者所在的命名空间将不再出现在的输出中。仅在无法分配时失败，而仅在实际用户 ID（real UID）与有效用

AI Predicted 7.8 Difficulty: Moderate EPSS 0.16% · P5 Updated Oct 23, 2026

Possible ATT&CK Techniques 1 AI

T1069.006

Affected Version Matrix 18

Vendor	Product	Version Range	Status
Linux	Linux	`a98621a0f187a934c115dcfe79a49520ae892111< 56fe03a0c05dba4c5f6a23c391f96de1614a098c`	affected
		`a98621a0f187a934c115dcfe79a49520ae892111< 0b6f31a3c0b16066f812e94b52a704174a6f23cd`	affected
		`27ae6b17c9ba7ff353ab0906297f08aa845782b4`	affected
		`297261b343371c4f0b31055d53d285138ec21565`	affected
		`813a47b0309097da71781ee4ac11922e39b67d55`	affected
		`6e608e3e5ce12ce7fd21e46212eccca37f917d0e`	affected
		`a261fccdb4ac58ec5ba6aa1d92a6cc418fff301f`	affected
		`665dc1ed16357988d439fc5bbc860ee36f540d81`	affected
… +10 more rows

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Vulnerability Information

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Vulnerability Title

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

Source: CVE Program / CVE List V5

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.

Source: CVE Program / CVE List V5

CVSS Information

N/A

Source: CVE Program / CVE List V5

Vulnerability Type

N/A

Source: CVE Program / CVE List V5

Affected Products

Vendor	Product	Affected Versions	CPE	Subscribe
Linux	Linux	a98621a0f187a934c115dcfe79a49520ae892111 ~ 56fe03a0c05dba4c5f6a23c391f96de1614a098c	-
Linux	Linux	7.1	-

II. Public POCs for CVE-2026-98983

#	POC Description	Source Link	Shenlong Link

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III. Intelligence Information for CVE-2026-98983

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Patches & Fixes for CVE-2026-98983 (2)

https://www.cve.org/CVERecord?id=CVE-2026-98983

Same Patch Batch · Linux · 2026-10-23 · 217 CVEs total

CVE-2026-98959	9.8 CRITICAL	btrfs: fix xattr replace when multiple xattrs are packed in the same item
CVE-2026-99078	9.8 CRITICAL	net/mlx5e: Prevent stale XSK buffer release on MPWQE refill retry
CVE-2026-99079	9.8 CRITICAL	net/mlx5e: Prevent stale XSK buffer release on refill retry
CVE-2026-98988	8.8 HIGH	namespace: keep covered mounts covered in OPEN_TREE_NAMESPACE
CVE-2026-99083	8.8 HIGH	ksmbd: fix heap out-of-bounds write in krb5_authenticate()
CVE-2026-99082	8.8 HIGH	KVM: x86: Use active memslots for the per-vCPU MMIO cache
CVE-2026-98870	8.8 HIGH	ksmbd: remove stale channels from all sessions on teardown
CVE-2026-98980	8.8 HIGH	namei: don't reveal overmounted entries in refwalk
CVE-2026-98981	8.8 HIGH	namespace: unhash a dentry before detaching the mounts on it
CVE-2026-99042	8.4 HIGH	io_uring/net: populate CONNECT filter fields for 24-byte sockaddr_in6
CVE-2026-98978	8.4 HIGH	namespace: never expire a locked mount
CVE-2026-99064	8.1 HIGH	cipso: adjust cached option offsets when removing CIPSO
CVE-2026-98968	8.1 HIGH	amt: send the relay's General Query directly from the receive path
CVE-2026-98944	7.8 HIGH	HID: steam: Refactor registration
CVE-2026-99053	7.8 HIGH	tipc: hold a reference to nodes found by link name
CVE-2026-99054	7.8 HIGH	tipc: destroy topsrv workqueues before closing connections
CVE-2026-99056	7.8 HIGH	strparser: make sure __strp_recv isn't running before tearing down the parser
CVE-2026-99002	7.8 HIGH	drm/vmwgfx: validate pitch coming from userspace
CVE-2026-98899	7.8 HIGH	netfilter: ipset: mark the rcu locked areas properly
CVE-2026-99006	7.8 HIGH	drm/i915/gem: Prevent overstepping exec array boundary

Showing top 20 of 217 CVEs. View all on vendor page → →

IV. Related Vulnerabilities

Same product: Linux

Same vendor: Linux