{"id":"CVE-2026-98976","title":"namespace: keep the lock on a mount that a propagated copy is moved beneath","summary":"In the Linux kernel, the following vulnerability has been resolved:\n\nnamespace: keep the lock on a mount that a propagated copy is moved beneath\n\nattach_recursive_mnt() transfers MNT_LOCKED from the top mount to the\nmount that is moved b…","severity":"none","vendor":"Linux","product":"Linux","affected":["Linux >= c62a4766937edec2962d52e583276b459b739f2d < f1f0c24ca701d7d3061c7f69f7450f1734c11745","Linux >= c62a4766937edec2962d52e583276b459b739f2d < d74d66aa708ccf2bc0b1e265a83fed0f2308d5c4","Linux 7.1"],"published":"2026-10-23","updated":"2026-10-23","sourceUpdated":"2026-10-23T12:19:49.363Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-98976","references":[{"url":"https://git.kernel.org/stable/c/f1f0c24ca701d7d3061c7f69f7450f1734c11745"},{"url":"https://git.kernel.org/stable/c/d74d66aa708ccf2bc0b1e265a83fed0f2308d5c4"}],"tags":["cve.org"],"ingestedAt":"2026-10-23T13:24:55.550Z","slug":"CVE-2026-98976","body":"## Overview\n\nIn the Linux kernel, the following vulnerability has been resolved:\n\nnamespace: keep the lock on a mount that a propagated copy is moved beneath\n\nattach_recursive_mnt() transfers MNT_LOCKED from the top mount to the\nmount that is moved beneath it with MOVE_MOUNT_BENEATH. This allows the\nowner of a user namespace to replace its locked /proc or its root. The\nmount beneath takes on the job of covering the underlying mountpoint\nallowing the top mount to be unmounted.\n\nConsider two mount namespaces:\n\n(H) The host H has a shared mount P with a secret in P/d\n(Z) Z is a user namespace made from M. Its copy of P receives\n    propagation from the host's P and its copy of M's cover on P/d is\n    locked Z's owner must not get to see P/d.\n\nNow (H) mounts X on P/d. This propagates into (Z). The copy of X lands\nbeneath (Z)'s locked cover. The locked property is transfered from (Z)'s\ncover to the copy of X propagated beneath it. The cover is now unlocked.\n\nNow (H) unmounts X again. The copy of X in (Z) gets unmounted and the\ncovering mount is left unlocked on top of P/d. (Z) can now unmount it:\n\n    Z: umount2(P/d)             = EINVAL            /* the cover is locked */\n    H: mount X on P/d, umount X                     /* both propagate into Z /*\n    Z: umount2(P/d)             = 0                 /* the cover is now unlocked */\n    Z: read P/d/secret          = \"covered-by-root\" /* secret revealed */\n\nSo only transfer the locked property to the mount beneath for mounts the\ncaller has placed. A propagated copy that lands beneath a locked mount\nis locked as well so that the mount at the bottom of the stack carries a\nlock the way every check expects. The mount on top of it remains locked\nto ensure that it keeps covering even if the propagated mount is\nunmounted again.\n\n## Affected\n\n- `Linux >= c62a4766937edec2962d52e583276b459b739f2d < f1f0c24ca701d7d3061c7f69f7450f1734c11745`\n- `Linux >= c62a4766937edec2962d52e583276b459b739f2d < d74d66aa708ccf2bc0b1e265a83fed0f2308d5c4`\n- `Linux 7.1`\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"sunlit","depthScore":3,"depthScoreParts":{"impact":2.8,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}