CVE-2026-98979 (GCVE-0-2026-98979)
Vulnerability from cvelistv5
Published
2026-10-23 12:19
Modified
2026-10-30 12:40
Severity ?
VLAI Severity ?
EPSS score ?
Summary
In the Linux kernel, the following vulnerability has been resolved:
namespace: refuse an automount below a mount that is in no namespace
It's possible to add autmounts even when the parent mount isn't in the
mount namespace of the caller. The only requirement we have is that the
parent mount namespace must not be NULL, i.e., unmounted.
Problem is that clone_private_mount() has MNT_NS_INTERNAL which makes
that trivially true. So that passes the test and attach_recursive_mnt()
accepts that as a mount point and funny enough, count_mounts()
dereferences MNT_NS_INTERNAL. The problem is it is an error pointer...
So we can reach this in userspace via fanotify. A filesystem mark on the
lower filesystem of an overlay reports paths on the layer clone and
reading the event hands out a descriptor on it. For example with debugfs
as the lower layer it goes kaboom:
openat(evfd, "tracing", O_DIRECTORY)
Oops: general protection fault
KASAN: null-ptr-deref in range [0x1d0-0x1d7]
RIP: 0010:count_mounts+0x35/0x200
attach_recursive_mnt
finish_automount
And since that sleeping beauty happens under namespace_sem held for
writing every mount operation on the system blocks from then on.
Congrats.
Use is_mounted() instead which rejects unmounted and internal mounts
alike. The open fails with EINVAL just as it did before
clone_private_mount() used MNT_NS_INTERNAL.
References
Impacted products
| Vendor | Product | Version | ||
|---|---|---|---|---|
| Linux | Linux |
Version: df820f8de4e481222b17f9bcee7b909ae8167529 Version: df820f8de4e481222b17f9bcee7b909ae8167529 Version: df820f8de4e481222b17f9bcee7b909ae8167529 Version: df820f8de4e481222b17f9bcee7b909ae8167529 Version: df820f8de4e481222b17f9bcee7b909ae8167529 Version: df820f8de4e481222b17f9bcee7b909ae8167529 Version: df820f8de4e481222b17f9bcee7b909ae8167529 Version: df820f8de4e481222b17f9bcee7b909ae8167529 |
||
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"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnamespace: refuse an automount below a mount that is in no namespace\n\nIt\u0027s possible to add autmounts even when the parent mount isn\u0027t in the\nmount namespace of the caller. The only requirement we have is that the\nparent mount namespace must not be NULL, i.e., unmounted.\n\nProblem is that clone_private_mount() has MNT_NS_INTERNAL which makes\nthat trivially true. So that passes the test and attach_recursive_mnt()\naccepts that as a mount point and funny enough, count_mounts()\ndereferences MNT_NS_INTERNAL. The problem is it is an error pointer...\n\nSo we can reach this in userspace via fanotify. A filesystem mark on the\nlower filesystem of an overlay reports paths on the layer clone and\nreading the event hands out a descriptor on it. For example with debugfs\nas the lower layer it goes kaboom:\n\n openat(evfd, \"tracing\", O_DIRECTORY)\n\n Oops: general protection fault\n KASAN: null-ptr-deref in range [0x1d0-0x1d7]\n RIP: 0010:count_mounts+0x35/0x200\n attach_recursive_mnt\n finish_automount\n\nAnd since that sleeping beauty happens under namespace_sem held for\nwriting every mount operation on the system blocks from then on.\nCongrats.\n\nUse is_mounted() instead which rejects unmounted and internal mounts\nalike. The open fails with EINVAL just as it did before\nclone_private_mount() used MNT_NS_INTERNAL."
}
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"providerMetadata": {
"dateUpdated": "2026-10-30T12:40:40.137Z",
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"url": "https://git.kernel.org/stable/c/95fb7c259b86f5521f04973040ad492f2bef6f82"
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},
{
"url": "https://git.kernel.org/stable/c/ba985ce08471c555af2a2fbe217c1bc2e72a6d8c"
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"title": "namespace: refuse an automount below a mount that is in no namespace",
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"cveId": "CVE-2026-98979",
"datePublished": "2026-10-23T12:19:52.523Z",
"dateReserved": "2026-09-25T10:25:14.383Z",
"dateUpdated": "2026-10-30T12:40:40.137Z",
"state": "PUBLISHED"
},
"dataType": "CVE_RECORD",
"dataVersion": "5.2"
}
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Sightings
| Author | Source | Type | Date |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or seen somewhere by the user.
- Confirmed: The vulnerability is confirmed from an analyst perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: This vulnerability was exploited and seen by the user reporting the sighting.
- Patched: This vulnerability was successfully patched by the user reporting the sighting.
- Not exploited: This vulnerability was not exploited or seen by the user reporting the sighting.
- Not confirmed: The user expresses doubt about the veracity of the vulnerability.
- Not patched: This vulnerability was not successfully patched by the user reporting the sighting.
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