VulnerabilityPublished 23 Oct 2026

CVE-2026-98990: Linux kernel · namespace: check a submount for references right before unmounting it

Affects Linux kernelSource CVE Database V5

Not known to be exploited · fixed in f6394281834492c6516a405a348b545ae698a331 : patch Linux kernel soon.

Data as of 26 Oct 2026, 17:30 UTC

Severity

High

Rated High by Threat Radar's AI analysis · CVSS not yet scored by NVD

EPSS: 0.1% chance of exploitation in 30 days – higher than 7% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in f6394281834492c6516a405a348b545ae698a331, d73f04e92c1aab78d96ac6cadb234c8a3a373d22, 18902a23ef36f83d32bafc58ae2484e6bb4bb8ef +6

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.

What to do

Upgrade to a fixed release listed under Affected software.

Affected software

Product	Affected	Fixed in
LinuxLinux	Affected >=4.1.40 <4.2 >=4.4.54 <4.5 >=4.9.15 <4.10 >=4.10.3 <4.11	Fixed in f6394281834492c6516a405a348b545ae698a331 d73f04e92c1aab78d96ac6cadb234c8a3a373d22 18902a23ef36f83d32bafc58ae2484e6bb4bb8ef 32bf92416614a1e3ff3524fc6b780259c7aad3ef 6e4012e571867868b545c91ca9d6095fdb709907 4.11 4.10 4.5 4.2
LinuxLinux	Affected =4.11	Fixed in–

AI-suggested

A fix for this vulnerability has been implemented in Linux kernel versions 4.2, 4.5, 4.10, and 4.11. Users and administrators should upgrade to these or later kernel versions to remediate the issue. No additional mitigation steps are necessary as the patch ensures proper reference checks before unmounting submounts.

Description

A Linux kernel vulnerability involving improper reference checks on submounts before unmounting them has been resolved. The flaw allowed a synchronous unmount operation to incorrectly pull out a busy mount that was still in use, potentially leading to an unreachable current working directory or other mount namespace inconsistencies. This issue affected automounted submounts with the MNT_SHRINKABLE flag, such as those used by NFS, AFS, CIFS, and certain debugfs mounts. The fix ensures that each mount is checked for references right before unmounting under appropriate locks to maintain linearity and correctness.

Impact

The vulnerability allows a busy mount that is still in use elsewhere to be unmounted synchronously, which can cause the current working directory to become unreachable and potentially disrupt system operations involving mount namespaces. This affects automounted submounts with the MNT_SHRINKABLE flag, impacting network file systems like NFS, AFS, CIFS, and certain debugfs mounts. The issue could lead to system instability or unexpected behavior in processes relying on these mounts.

Summary

CVE-2026-98990 is a vulnerability in the Linux kernel's namespace handling where shrink_submounts() and mark_mounts_for_expiry() functions collect mounts to unmount but do not properly verify if a mount is still busy at the time of unmounting. The unmounting of one mount alters the mount tree, causing propagate_umount() to move surviving overmounts in a way that can cause a busy mount to be unmounted synchronously while still in use. This leads to a mount marked MNT_SYNC_UMOUNT with active users, causing issues such as unreachable current working directories. The vulnerability specifically affects mounts with the MNT_SHRINKABLE flag, including automounted NFS, AFS, CIFS submounts, and certain debugfs mounts. The patch adds a check for each mount immediately before unmounting it while holding the same namespace_sem and mount_lock as the unmount operation, ensuring the algorithm remains linear and correct.

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What to do

Affected software

Description

AI analysisMachine-generated, updated 26 Oct 2026, 09:55 UTC

Technical details

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