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CVE-2026-98990

Linux: namespace: check a submount for references right before unmounting it

Linux LinuxOperating systems
Open in ThreatlineRecord JSON
CVSS
NoneNot scored
ExploitationNo known exploitationNot in CISA KEV, which does not prove it is unexploitedCISA KEV
Exploit odds (EPSS)No scoreNo FIRST EPSS score in this snapshot yet
Fixed in6e4012e571867868b545c91ca9d6095fdb709907Also 18902a23ef36f83d32bafc58ae2484e6bb4bb8ef, 32bf92416614a1e3ff3524fc6b780259c7aad3ef and 4 moreCVE List
Published23 Oct 2026Updated 23 Oct 2026CVE List

What fixes it

Show all 7 fixed versions

A fixed version on one release line is not the upgrade target for every line. Check your exact version and any vendor backports.

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.

Text from CVE List

Affected versions 20

  • Linuxaffected: 1064f874abc0d05eeed8993815f584d847b72486 before f6394281834492c6516a405a348b545ae698a331CVE List
  • Linuxaffected: 1064f874abc0d05eeed8993815f584d847b72486 before 6e4012e571867868b545c91ca9d6095fdb709907CVE List
  • Linuxaffected: 1064f874abc0d05eeed8993815f584d847b72486 before d73f04e92c1aab78d96ac6cadb234c8a3a373d22CVE List
  • Linuxaffected: 1064f874abc0d05eeed8993815f584d847b72486 before 18902a23ef36f83d32bafc58ae2484e6bb4bb8efCVE List
  • Linuxaffected: 1064f874abc0d05eeed8993815f584d847b72486 before 32bf92416614a1e3ff3524fc6b780259c7aad3efCVE List
  • Linuxaffected: 5e6ef5ef6eaf690faad3a7c6c665ebf45d7b6ccfCVE List
  • Linuxaffected: 839d42687dfce0ed0ea2c6bd8d707cc0e276fbe7CVE List
  • Linuxaffected: 808e83e5add13152bd4a88346487de68395c136bCVE List
  • Linuxaffected: 6de9d08a9718ee9c12ba6343c50141c2d633e3dcCVE List
  • Linuxaffected: 4.1.40 before 4.2CVE List
  • Linuxaffected: 4.4.54 before 4.5CVE List
  • Linuxaffected: 4.9.15 before 4.10CVE List
  • Linuxaffected: 4.10.3 before 4.11CVE List
  • Linuxaffected: 4.11CVE List
  • Linuxunaffected: all versions before 4.11CVE List
  • Linuxunaffected: 6.6.160 through 6.6.*CVE List
  • Linuxunaffected: 6.12.113 through 6.12.*CVE List
  • Linuxunaffected: 6.18.57 through 6.18.*CVE List
  • Linuxunaffected: 7.2.11 through 7.2.*CVE List
  • Linuxunaffected: 7.3CVE List

References 5