{"id":"CVE-2026-98988","title":"namespace: keep covered mounts covered in OPEN_TREE_NAMESPACE","summary":"In the Linux kernel, the following vulnerability has been resolved:\n\nnamespace: keep covered mounts covered in OPEN_TREE_NAMESPACE\n\nopen_tree(OPEN_TREE_NAMESPACE) creates a new mount namespace from a\ncopy of the tree at the given path. T…","severity":"none","vendor":"Linux","product":"Linux","affected":["Linux >= 9b8a0ba68246a61d903ce62c35c303b1501df28b < b8a94a405ddcf45e9470789e0a821d8f2aa4ca10","Linux >= 9b8a0ba68246a61d903ce62c35c303b1501df28b < 0febe278ec45b1ccdbe9bd5ff1ba365d8fd55e2a","Linux 7.0"],"published":"2026-10-23","updated":"2026-10-23","sourceUpdated":"2026-10-23T12:20:07.483Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-98988","references":[{"url":"https://git.kernel.org/stable/c/b8a94a405ddcf45e9470789e0a821d8f2aa4ca10"},{"url":"https://git.kernel.org/stable/c/0febe278ec45b1ccdbe9bd5ff1ba365d8fd55e2a"}],"tags":["cve.org"],"ingestedAt":"2026-10-23T13:24:55.546Z","slug":"CVE-2026-98988","body":"## Overview\n\nIn the Linux kernel, the following vulnerability has been resolved:\n\nnamespace: keep covered mounts covered in OPEN_TREE_NAMESPACE\n\nopen_tree(OPEN_TREE_NAMESPACE) creates a new mount namespace from a\ncopy of the tree at the given path. The caller needs to be privileged\nover its current user namespace because the new mount namespace will be\nowned by it. It doesn't need to be privileged over the mount namespace\nthe tree is copied from. An unprivileged user just needs to create a\nuser namespace first.\n\nThe copy follows the rules of a detached bind mount. Without\nAT_RECURSIVE only the mount itself is cloned and its children are left\nout. With AT_RECURSIVE unbindable mounts are skipped. Both is fine when\nthe caller has privileges over the source mount namespace because it\ncould unmount those mounts anyway. Not so for an unprivileged user in\nthat mount namespace. For them a mount namespace copy is what unshare()\ndoes. copy_mnt_ns() copies everything including unbindable mounts and\nlock_mnt_tree() makes sure nothing can be unmounted in the copy. Nothing\nthat was covered gets revealed.\n\ncreate_new_namespace() only does the locking and so the covered content\nis right there in the new mount namespace:\n\n  # mount -t tmpfs none /tmp/otn; mkdir /tmp/otn/covered\n  # echo hidden > /tmp/otn/covered/under.txt\n  # mount -t tmpfs none /tmp/otn/covered\n\n  uid 1000, after unshare(CLONE_NEWUSER):\n  fd = open_tree(AT_FDCWD, \"/tmp/otn\", OPEN_TREE_NAMESPACE);\n  setns(fd, CLONE_NEWNS);\n  open(\"/covered/under.txt\", O_RDONLY)  -> \"hidden\"\n\nCovering paths with mounts is how container runtimes mask parts of\n/proc and /sys and how admins hide things.\n\nWhen the caller's user namespace doesn't own the source mount namespace\ncopy the way unshare() does and refuse a non-recursive copy of a mount\nthat has anything mounted below the requested directory and copy\nunbindable mounts in a recursive copy. A caller that is privileged over\nthe source mount namespace sees no change.\n\n## Affected\n\n- `Linux >= 9b8a0ba68246a61d903ce62c35c303b1501df28b < b8a94a405ddcf45e9470789e0a821d8f2aa4ca10`\n- `Linux >= 9b8a0ba68246a61d903ce62c35c303b1501df28b < 0febe278ec45b1ccdbe9bd5ff1ba365d8fd55e2a`\n- `Linux 7.0`\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":[]}