CVE-2026-98988 (GCVE-0-2026-98988)
Vulnerability from cvelistv5 – Published: 2026-10-23 12:20 – Updated: 2026-10-24 14:09
VLAI
EPSS
VEX
Title
namespace: keep covered mounts covered in OPEN_TREE_NAMESPACE
Summary
In the Linux kernel, the following vulnerability has been resolved:
namespace: keep covered mounts covered in OPEN_TREE_NAMESPACE
open_tree(OPEN_TREE_NAMESPACE) creates a new mount namespace from a
copy of the tree at the given path. The caller needs to be privileged
over its current user namespace because the new mount namespace will be
owned by it. It doesn't need to be privileged over the mount namespace
the tree is copied from. An unprivileged user just needs to create a
user namespace first.
The copy follows the rules of a detached bind mount. Without
AT_RECURSIVE only the mount itself is cloned and its children are left
out. With AT_RECURSIVE unbindable mounts are skipped. Both is fine when
the caller has privileges over the source mount namespace because it
could unmount those mounts anyway. Not so for an unprivileged user in
that mount namespace. For them a mount namespace copy is what unshare()
does. copy_mnt_ns() copies everything including unbindable mounts and
lock_mnt_tree() makes sure nothing can be unmounted in the copy. Nothing
that was covered gets revealed.
create_new_namespace() only does the locking and so the covered content
is right there in the new mount namespace:
# mount -t tmpfs none /tmp/otn; mkdir /tmp/otn/covered
# echo hidden > /tmp/otn/covered/under.txt
# mount -t tmpfs none /tmp/otn/covered
uid 1000, after unshare(CLONE_NEWUSER):
fd = open_tree(AT_FDCWD, "/tmp/otn", OPEN_TREE_NAMESPACE);
setns(fd, CLONE_NEWNS);
open("/covered/under.txt", O_RDONLY) -> "hidden"
Covering paths with mounts is how container runtimes mask parts of
/proc and /sys and how admins hide things.
When the caller's user namespace doesn't own the source mount namespace
copy the way unshare() does and refuse a non-recursive copy of a mount
that has anything mounted below the requested directory and copy
unbindable mounts in a recursive copy. A caller that is privileged over
the source mount namespace sees no change.
Severity
8.8 (High)
Assigner
References
Impacted products
2 products
| Vendor | Product | Version | CPE status | |
|---|---|---|---|---|
| Linux | Linux |
Affected:
9b8a0ba68246a61d903ce62c35c303b1501df28b , < b8a94a405ddcf45e9470789e0a821d8f2aa4ca10
(git)
Affected: 9b8a0ba68246a61d903ce62c35c303b1501df28b , < 0febe278ec45b1ccdbe9bd5ff1ba365d8fd55e2a (git) |
guessed | |
| Linux | Linux |
Affected:
7.0
Unaffected: 0 , < 7.0 (semver) Unaffected: 7.2.11 , ≤ 7.2.* (semver) Unaffected: 7.3 , ≤ * (original_commit_for_fix) |
guessed |
{
"containers": {
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"defaultStatus": "unaffected",
"product": "Linux",
"programFiles": [
"fs/namespace.c"
],
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"vendor": "Linux",
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"version": "7.0"
},
{
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"status": "unaffected",
"version": "0",
"versionType": "semver"
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"status": "unaffected",
"version": "7.3",
"versionType": "original_commit_for_fix"
}
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"cpeApplicability": [
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"nodes": [
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"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
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"versionStartIncluding": "7.0",
"vulnerable": true
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{
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"descriptions": [
{
"lang": "en",
"value": "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. The caller needs to be privileged\nover its current user namespace because the new mount namespace will be\nowned by it. It doesn\u0027t 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 \u003e /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) -\u003e \"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\u0027s user namespace doesn\u0027t 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."
}
],
"metrics": [
{
"cvssV3_1": {
"baseScore": 8.8,
"baseSeverity": "HIGH",
"vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H",
"version": "3.1"
},
"scenarios": [
{
"lang": "en",
"value": "AV:L - The local open_tree(..., OPEN_TREE_NAMESPACE) syscall reaches vfs_open_tree()-\u003eopen_new_namespace()-\u003ecreate_new_namespace(); the triggering path and flags originate from that local syscall, not any network protocol.\nAC:L - After unshare(CLONE_NEWUSER), the attacker selects an ancestor containing a covered child and omits AT_RECURSIVE; vulnerable create_new_namespace() deterministically calls __do_loopback()-\u003eclone_mnt(), leaving the child out. There is no race or outside event.\nPR:L - vfs_open_tree() checks only ns_capable(current_user_ns(), CAP_SYS_ADMIN) for this flag; unshare(CLONE_NEWUSER) gives an ordinary user that capability, and mntns_install() accepts it for the child-owned namespace. No capability in the source mount namespace is required.\nUI:N - The attacker invokes unshare(), open_tree(), setns(), and the final file operation; create_new_namespace() needs no victim-triggered mount or file access.\nS:C - create_new_namespace() copies a tree from the source namespace owned by ns-\u003euser_ns into one owned by the attacker\u0027s different current_user_ns() while dropping covering children, crossing the mount-namespace sandbox boundary.\nC:H - For the nonrecursive path, clone_mnt() copies only the selected parent mount; after setns(), lookup falls through the omitted mountpoint to the full underlying directory tree, permitting unbounded reads of covered files allowed by inode DAC.\nI:H - clone_mnt() preserves the writable parent\u0027s mnt_flags but omits a read-only or masking child mount, so open(), rename(), and unlink() can modify or delete the entire formerly protected subtree where DAC permits.\nA:H - The same create_new_namespace() primitive can expose a writable covered service tree; truncating or deleting protected executables, configuration, or data can make that service persistently unavailable."
}
]
}
],
"providerMetadata": {
"dateUpdated": "2026-10-24T14:09:51.817Z",
"orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"shortName": "Linux"
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"references": [
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"url": "https://git.kernel.org/stable/c/b8a94a405ddcf45e9470789e0a821d8f2aa4ca10"
},
{
"url": "https://git.kernel.org/stable/c/0febe278ec45b1ccdbe9bd5ff1ba365d8fd55e2a"
}
],
"title": "namespace: keep covered mounts covered in OPEN_TREE_NAMESPACE",
"x_generator": {
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"cveMetadata": {
"assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"assignerShortName": "Linux",
"cveId": "CVE-2026-98988",
"datePublished": "2026-10-23T12:20:07.483Z",
"dateReserved": "2026-09-25T10:25:14.384Z",
"dateUpdated": "2026-10-24T14:09:51.817Z",
"state": "PUBLISHED"
},
"dataType": "CVE_RECORD",
"dataVersion": "5.2",
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"cve": "CVE-2026-98988",
"date": "2026-10-24",
"epss": "0.00198",
"percentile": "0.09008"
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}
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"cveTags": [],
"descriptions": [
{
"lang": "en",
"value": "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. The caller needs to be privileged\nover its current user namespace because the new mount namespace will be\nowned by it. It doesn\u0027t 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 \u003e /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) -\u003e \"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\u0027s user namespace doesn\u0027t 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."
}
],
"id": "CVE-2026-98988",
"lastModified": "2026-10-24T14:16:50.990",
"metrics": {
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{
"cvssData": {
"attackComplexity": "LOW",
"attackVector": "LOCAL",
"availabilityImpact": "HIGH",
"baseScore": 8.8,
"baseSeverity": "HIGH",
"confidentialityImpact": "HIGH",
"integrityImpact": "HIGH",
"privilegesRequired": "LOW",
"scope": "CHANGED",
"userInteraction": "NONE",
"vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H",
"version": "3.1"
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"impactScore": 6.0,
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"type": "Secondary"
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"published": "2026-10-23T13:17:20.753",
"references": [
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"url": "https://git.kernel.org/stable/c/0febe278ec45b1ccdbe9bd5ff1ba365d8fd55e2a"
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{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
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"sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"vulnStatus": "Received"
}
}
}
}
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