VulnerabilityPublished 23 Oct 2026Updated 24 Oct 2026

CVE-2026-98981: Linux kernel · namespace: unhash a dentry before detaching the mounts on it

Source GCVE Database

Authoritative record:CVE-2026-98981· High 8.8

Not known to be exploited · CVSS 8.8 High · fixed in db90eecbde319527aa9480c039d32a0f5fe80574 : patch Linux kernel soon.

Data as of 26 Oct 2026, 14:05 UTC

CVSS 3.1 base score

8.8High

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.1% chance of exploitation in 30 days – higher than 5% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in db90eecbde319527aa9480c039d32a0f5fe80574, d29cd99db3db74cf3447be74d25740981789d461, 8300de4aa5d09061bfcf2af5b52c0cdba3873185 +2

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H

Attack Vector: Local
Attack Complexity: Low
Privileges Required: Low
User Interaction: None
Scope: Changed
Confidentiality: High
Integrity: High
Availability: High

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Local: The vulnerable component is not bound to the network stack and the attacker’s path is via read/write/execute capabilities. Either: the attacker exploits the vulnerability by accessing the target system locally (e.g., keyboard, console), or remotely (e.g., SSH); or the attacker relies on User Interaction by another person to perform actions required to exploit the vulnerability (e.g., tricking a legitimate user into opening a malicious document).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: Low: The attacker is authorized with (i.e., requires) privileges that provide basic user capabilities that could normally affect only settings and files owned by a user. Alternatively, an attacker with Low privileges may have the ability to cause an impact only to non-sensitive resources.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Changed: An exploited vulnerability can affect resources beyond the security scope managed by the security authority of the vulnerable component. In this case, the vulnerable component and the impacted component are different and managed by different security authorities.
Confidentiality: High: There is total loss of confidentiality, resulting in all resources within the impacted component being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact.
Integrity: High: There is a total loss of integrity, or a complete loss of protection. For example, the attacker is able to modify any/all files protected by the impacted component. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to the impacted component.
Availability: High: There is total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 23 Oct 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

ghsa-9hg7-cp6v-469m

What to do

Upgrade to a fixed release listed under Affected software.

Affected software

Product	Affected	Fixed in
LinuxLinux	Affected ≥ 8ed936b5671bfb33d89bc60bdcc7cf0470ba52fe, < db90eecbde319527aa9480c039d32a0f5fe80574	Fixed in db90eecbde319527aa9480c039d32a0f5fe80574
LinuxLinux	Affected ≥ 8ed936b5671bfb33d89bc60bdcc7cf0470ba52fe, < d29cd99db3db74cf3447be74d25740981789d461	Fixed in d29cd99db3db74cf3447be74d25740981789d461
LinuxLinux	Affected ≥ 8ed936b5671bfb33d89bc60bdcc7cf0470ba52fe, < 8300de4aa5d09061bfcf2af5b52c0cdba3873185	Fixed in 8300de4aa5d09061bfcf2af5b52c0cdba3873185
LinuxLinux	Affected ≥ 8ed936b5671bfb33d89bc60bdcc7cf0470ba52fe, < 528b383dc35d1e5caf64ddf5d35f983ae543b0d0	Fixed in 528b383dc35d1e5caf64ddf5d35f983ae543b0d0
LinuxLinux	Affected ≥ 8ed936b5671bfb33d89bc60bdcc7cf0470ba52fe, < 8d71bfc9b3fc15d7103e82ea9dc5057541866e46	Fixed in 8d71bfc9b3fc15d7103e82ea9dc5057541866e46
LinuxLinux	Affected =3.18	Fixed in–

Description

In the Linux kernel, the following vulnerability has been resolved: namespace: unhash a dentry before detaching the mounts on it unlink(), rmdir() and rename() remove the entry from the filesystem, call detach_mounts() on the entry with the inode locked and then call d_delete() once the inode is unlocked. The thing is that between detach_mounts() and d_delete() the dentry is still hashed and positive. But after detach_mounts() nothing covers the dentry anymore. A lookup that finds this dentry in the dcache can uncover what the mounts hid. That's a problem when unlinking files or directories that are mountpoints in other mount namespaces. Everybody who had the underlying entry covered can race the detach_mount() call until d_delete() has run. The race window isn't all that small. It encompasses namespace_unlock() with a full synchronize_rcu_expedited() grace period and the inode_unlock() of the entry. In my experiments three walkers that kept trying read an overmounted file in 11938 of the 16140 unlinks that removed its mountpoint from a bind mount of the filesystem within a minute. Fun fact, d_invalidate() has the same ordering problem but gets it right. It unhashes the dentry first and detaches the mounts afterwards. Let's do the same in __detach_mounts(): - A lookup that hasn't found the dentry yet misses it in the dcache and waits for the directory lock that the caller holds until the name is gone for good. - A lockless lookup that found it already fails the mount_lock check while the dentry still counts as a mountpoint and the d_seq check once it doesn't, and retries. This fixes the lockless path. We still need to fix the reference count lookup in a follow-up patch. So d_drop() the dentry. The dentry stays positive and held but can't be found anymore. Then proceed with the detach and unlink. Reproducer: The reads were counted with the program below, three walkers for 60 s in a VM with 4 CPUs. The race window is stretched with the debug patch pasted here. fs.detach_race_walk_us sleeps in lookup_fast() once it found a mountpoint dentry and before its mounts are crossed. fs.detach_race_unlink_us sleeps in vfs_unlink() between detach_mounts() and d_delete(). // SPDX-License-Identifier: GPL-2.0 /* * unlink_covered: unlink a file that is a mountpoint in a detached copy of * its mount, against lookups that open it through that copy. * * A is a tmpfs with the file f1 (content SECRET_F) and the plain file * MARK_A. A' is an open_tree(OPEN_TREE_CLONE) copy of A with MARK_A bound * on A'/f1, held through an O_PATH fd on its root once the tree fd is * closed. Walkers open f1 through that fd while the driver unlinks A/f1, * where nothing is mounted on it. A walker may read MARK_A or get ENOENT. * A read of SECRET_F is a hit: the name was found after its mount was * gone. The lockless walks use openat2(RESOLVE_CACHED). * * usage: unlink_covered [-t seconds] [-w walkers] */ #ifndef _GNU_SOURCE #define _GNU_SOURCE #endif #include <errno.h> #include <fcntl.h> #include <pthread.h> #include <stdatomic.h> #include <stdio.h> #include <stdlib.h> #include <string.h> #include <unistd.h> #include <sys/mount.h> #include <sys/stat.h> #include <sys/syscall.h> #include <linux/openat2.h> #ifndef __NR_open_tree #define __NR_open_tree 428 #endif #ifndef __NR_move_mount #define __NR_move_mount 429 #endif #ifndef __NR_openat2 #define __NR_openat2 437 #endif #ifndef OPEN_TREE_CLONE #define OPEN_TREE_CLONE 1 #endif #ifndef OPEN_TREE_CLOEXEC #define OPEN_TREE_CLOEXEC O_CLOEXEC #endif #ifndef MOVE_MOUNT_F_EMPTY_PATH #define MOVE_MOUNT_F_EMPTY_PATH 0x00000004 #endif #define WORK "/tmp/uc" #define ADIR WORK "/A" static int duration = 60, nwalkers = 3; static atomic_int stop, writer_waiting; static pthread_rwlock_t cur_lock = PTHREAD_RWLOCK_INITIALIZER; static int cur_fd = -1; /* the root of A', -1 wh ---truncated---

References

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