CVE-2026-98990: Linux kernel · namespace: check a submount for references right before unmounting it
Source GCVE Database
Not known to be exploited · fixed in f6394281834492c6516a405a348b545ae698a331 : patch Linux kernel soon.
Data as of 26 Oct 2026, 16:00 UTC
Rated by Threat Radar · 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.
What to do
Upgrade to a fixed release listed under Affected software.
Affected software
| Product | Affected | Fixed in |
|---|---|---|
| LinuxLinux | Affected
| Fixed in
|
| LinuxLinux | Affected
| Fixed in– |
Description
In the Linux kernel, the following vulnerability has been resolved: namespace: check a submount for references right before unmounting it shrink_submounts() and mark_mounts_for_expiry() first collect all the mounts they are allowed to unmount and then unmount them. Whether a mount is busy is decided by propagate_mount_busy() on the tree. But unmounting the first mount changes the tree that the second one propagates into. propagate_umount() moves a surviving overmount off a copy it unmounts and mounts it where the copy was mounted. If that's where the propagated copy of the second victim is looked up the overmount becomes a candidate of the second umount_tree(). It's childless and so trim_one() commits it without looking at its reference count. So a synchronous umount pulls out a busy mount that is in use somewhere else and marks it MNT_SYNC_UMOUNT while it has users: umount2(/tmp/plshrink/p1, 0) = 0 errno 0 cwd is (unreachable) The same two umounts requested one after the other fail with EBUSY. This needs a mount with MNT_SHRINKABLE, i.e., automounted submounts of NFS, AFS and CIFS or the tracefs mount below debugfs. Bind mounts inherit the flag. Check each mount right before it is unmounted under the same hold of namespace_sem and mount_lock as the umount itself. Make sure that the algorithm stays linear.
References
- nvd.nist.gov/vuln/detail/CVE-2026-98990 (opens in a new tab)
- git.kernel.org/stable/c/18902a23ef36f83d32bafc58ae2484e6bb4bb8ef (opens in a new tab)
- git.kernel.org/stable/c/32bf92416614a1e3ff3524fc6b780259c7aad3ef (opens in a new tab)
- git.kernel.org/stable/c/6e4012e571867868b545c91ca9d6095fdb709907 (opens in a new tab)
- git.kernel.org/stable/c/d73f04e92c1aab78d96ac6cadb234c8a3a373d22 (opens in a new tab)
- git.kernel.org/stable/c/f6394281834492c6516a405a348b545ae698a331 (opens in a new tab)