CVE-2026-99281

tun: Require CAP_NET_ADMIN to attach to an ownerless device

Products / packages Linux

Published 07/11/2026, 14:08:47 UTC

Severity and exploitation

Not in CISA KEV

KEV coverage does not rule out exploitation.

KEV checked 14/11/2026, 21:10:34 UTC

Linux · CVSS:3.1 · 7.8

Assessment vector

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Severity

high7.8

CVSS measures technical severity, not the likelihood of an attack.

Known exploitation

Not listed in the checked CISA KEV catalog

Absence from CISA KEV does not rule out attacks.

Public exploit

Not established by this record

Missing evidence does not mean no public exploit exists.

Remediation

Fix status not established

No structured fix or guidance is available here. Check the latest publisher advisory.

What this means

In the Linux kernel, the following vulnerability has been resolved:

Source excerpt · Linux

Attack conditions

tun: Require CAP_NET_ADMIN to attach to an ownerless device Twenty years ago I made creating a tuntap device require CAP_NET_ADMIN in commit ca6bb5d7ab22 ("[NET]: Require CAP_NET_ADMIN to create tuntap devices.") In 2024, commit 3ca459eaba1bf ("tun: fix group permission check") tried to fix things to be saner: only require the user or the group to match, in line with standard POSIX permissions, and require CAP_NET_ADMIN if neither the user nor group authorised the access (although it put the CAP_NET_ADMIN check first, and would wrongly have reported the capability as having been used even when it was not).

Excerpt from the original source description below.

Review supporting sources →

Affected versions

Check the exact model, release, and any platform requirements against your installation.

Linux · Linux

Linux

4 ranges

Linux version evidence

Check a product version

Compare with this publisher’s ranges. This does not inspect your installation.

affected

ca6bb5d7ab22ac79f608fe6cbc6b12de6a5a19f0 → before e0d98aab41b79b88609f33fb4d8e7a80ab8f648d

git versions

ca6bb5d7ab22ac79f608fe6cbc6b12de6a5a19f0 → before 2f92c0286cfd58bff9d6d54c01a771073d5eb775

git versions

ca6bb5d7ab22ac79f608fe6cbc6b12de6a5a19f0 → before e53d1cf05da8ea58a5743b7ce5894fb51b0b9700

git versions

ca6bb5d7ab22ac79f608fe6cbc6b12de6a5a19f0 → before ffdf678dd16610e3f006dac904bd37c09684673c

git versions

Other versions: unaffected

Linux · Linux

Linux

6 ranges

Linux version evidence

Check a product version

Compare with this publisher’s ranges. This does not inspect your installation.

affected

2.6.18

unaffected

0 → before 2.6.18

semver versions

6.12.117 → through 6.12.*

semver versions

6.18.61 → through 6.18.*

semver versions

7.3.2 → through 7.3.*

semver versions

7.4-rc1 → through *

original_commit_for_fix versions

Other versions: affected

Automatic dependency matching is unavailable for this record. Use the product evidence and publisher’s instructions to check your installation.

What to do

Compare your installed product and version with the affected versions above. A matching product name alone does not confirm exposure.

No structured fix or remediation guidance is available here. Check the full source description and vendor’s latest advisory for a patch or workaround; do not assume another version is safe.

cve.new guidance unless attributed to a publisher. This page does not inspect your installation.

Public exploit evidence

No public exploit reference is identified in the imported evidence. This is not a claim that no exploit exists.

Original source description

Read the full publisher description

In the Linux kernel, the following vulnerability has been resolved:

tun: Require CAP_NET_ADMIN to attach to an ownerless device

Twenty years ago I made creating a tuntap device require CAP_NET_ADMIN in commit ca6bb5d7ab22 ("[NET]: Require CAP_NET_ADMIN to create tuntap devices.")

The idea was to allow the permissions on /dev/net/tun to be relaxed to 0666 and thus allow owners of tun devices assigned with TUNSETOWNER to actually open it and get at their devices.

What we missed at the time was that persistent devices with no owner were already essentially world-consumable, and anyone who could open the device node could also attach to those.

Even then, using persistent devices with no explicitly set owner — on the (false) presumption that CAP_NET_ADMIN would be required to open them — wasn't an egregious userspace bug. There are cases where it does make sense to separate the creation/configuration of the netdevice, from the process which shovels packets into it.

Since then, TUNSETGROUP was added a year later in commit 8c644623fe7e ("[NET]: Allow group ownership of TUN/TAP devices."). Its commit message noted that if both uid and gid are set, both have to match (in itself a bizarre choice) — but still not that with neither set, no permission at all was required.

Then in 2012 commit c8d68e6be1c3 ("tuntap: multiqueue support") allowed new queues to be attached to a device from the moment of its creation, with no way for userspace to close the race between creation and a subsequent TUNSET{OWNER,GROUP}.

In 2024, commit 3ca459eaba1bf ("tun: fix group permission check") tried to fix things to be saner: only require the user or the group to match, in line with standard POSIX permissions, and require CAP_NET_ADMIN if neither the user nor group authorised the access (although it put the CAP_NET_ADMIN check first, and would wrongly have reported the capability as having been used even when it was not).

That fix was reverted in commit a70c7b3cbc06 ("tun: revert fix group permission check") due to allegedly causing a regression in an selinux test suite which expected the attachment to succeed when authorised by none of user, group, nor CAP_NET_ADMIN: https://lore.kernel.org/netdev/CAFqZXNtkCBT4f+PwyVRmQGoT3p1eVa01fCG_aNtpt6dakXncUg@mail.gmail.com/

We should not break UAPI. But we don't have to consider an selinux test case which deliberately exercises a security flaw to be UAPI worth preserving either. To which end, I have fixed it in selinux-testsuite commit b2f894f0016b ("tests/tun_tap: set an owner on the device for the relabel tests").

So: fix the lack of CAP_NET_ADMIN check on devices which haven't been assigned an owner or group, while leaving the weird tun ownership model as it was (user and group have to match, if both are set). If someone still wants to fix the latter (which wasn't actually the reason the previous attempt was reverted), they can do it under separate cover.

Permit attaching to an existing device only if an owner and/or group was set and the caller matches all that were set, or if the caller has CAP_NET_ADMIN. The only behavioural change is that a device with no owner or group now requires CAP_NET_ADMIN to attach — precisely the loophole we want to close.

And put the CAP_NET_ADMIN check in the right place this time.

References

4 sources

git.kernel.org/stable/c/e0d98aab41b79b88609f33fb4d8e7a80ab8f648d

Source referenceLinux

git.kernel.org/stable/c/2f92c0286cfd58bff9d6d54c01a771073d5eb775

Source referenceLinux

git.kernel.org/stable/c/e53d1cf05da8ea58a5743b7ce5894fb51b0b9700

Source referenceLinux

git.kernel.org/stable/c/ffdf678dd16610e3f006dac904bd37c09684673c

Source referenceLinux

Inside the record

Evidence available

Package identity · not supplied

Version evidence

Remediation guidance · not supplied

Weakness classification · not supplied

Additional publishers · not supplied

Describes the evidence in this view, not whether the product is safe.

Original records

CVE-2026-99281

View the latest unmodified CVE JSON from the official source. It may be newer than this imported page.

cve.new JSON →

Environment requirements

These conditions apply together as specified by the publisher. A matching product name alone does not establish exposure.

Linux · platform conditions

Any condition may hold

Vulnerable product

cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*

From (inclusive): 2.6.18

After:

Through (inclusive):

Before: 6.12.117

Vulnerable product

cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*

From (inclusive): 2.6.18

After:

Through (inclusive):

Before: 6.18.61

Vulnerable product

cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*

From (inclusive): 2.6.18

After:

Through (inclusive):

Before: 7.3.2

Vulnerable product

cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*

From (inclusive): 2.6.18

After:

Through (inclusive):

Before: 7.4-rc1

Applicability preview

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Contributing organizations · 1

Linux

Assigning organization

2026-11-10

Timeline

All times UTC

7 Nov 2026, 14:08
Advisory published
Publication date supplied by the source.
10 Nov 2026, 18:15
Source updated
Latest modification date supplied by the source.
10 Nov 2026, 18:23
Last imported by cve.new
Latest catalog import, not the date we first saw this advisory.

What changed

Follow changes

CVE · CVE-2026-992812026-11-10

Observed 2026-11-10T18:23:14.869Z · upstream updated 2026-11-10T18:15:28.611Z

Product or version evidence changed

before

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after

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References changed

before

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after

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Environment requirements changed

before

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after

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CVE · CVE-2026-992812026-11-10
Observed 2026-11-10T17:01:33.028Z · upstream updated 2026-11-10T16:57:40.816Z
Severity assessment changed
before
[]
after
[ { "source": "Linux", "vector": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H", "score": 7.8 } ]

Large field values are marked as truncated previews. Original source snapshots remain retained.

Showing up to 50 most recent observed changes.

Reading the signals

Severity · CVSS: Technical impact and attack conditions. The headline is the highest imported catalog score; sources may disagree.
Observed exploitation · KEV: An absent or unavailable KEV listing does not establish that exploitation has not occurred.
Predicted exploitation · EPSS: No EPSS estimate available in this record.

Record identifiers

Aliases: None recorded

Source evidence

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CVE CVE-2026-99281

Enrichment coverage

NVDAvailable

Checked 07/11/2026, 14:20:32 UTC

GHSANo result

Checked 07/11/2026, 14:20:32 UTC

EUVDNo result

Checked 07/11/2026, 14:20:33 UTC

EPSSNo result

Checked 07/11/2026, 14:20:32 UTC

Additional source evidence

NVD · CVE-2026-99281Checked 07/11/2026, 14:20:32 UTC

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tun: Require CAP_NET_ADMIN to attach to an ownerless device

Severity and exploitation

What this means

Attack conditions

Affected versions

Linux

affected

unaffected

unknown

Linux

affected

unaffected

unknown

What to do

Public exploit evidence

Original source description

References

Inside the record

Evidence available

Original records

Environment requirements

Timeline

Advisory published

Source updated

Last imported by cve.new

What changed