* [CVE-2026-98988][IMPORTANT] namespace: keep covered mounts covered in OPEN_TREE_NAMESPACE
@ 2026-10-26 20:38 21% AL-KERNEL
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From: AL-KERNEL @ 2026-10-26 20:38 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-98988
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: NO
Patch: namespace: keep covered mounts covered in OPEN_TREE_NAMESPACE
Commit: b8a94a405ddcf45e9470789e0a821d8f2aa4ca10
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b8a94a405ddcf45e9470789e0a821d8f2aa4ca10
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98988
Analysis date: Mon, 26 Oct 2026 16:38:41 -0400
ActionableScore: 7
ActionableScore lower bound: unknown
Actionable bucket: Strong Important candidate
Manual review required: YES
Summary:
An unprivileged user namespace could clone a foreign mount tree while omitting covering mounts, exposing administrator- or runtime-masked content that remained readable under ordinary DAC/LSM policy.
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ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98988 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98988
The original announcement does not normally provide a security severity
estimate, CVSS assessment, or enough information to determine whether the
reported kernel bug represents a practically relevant security issue.
This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin. It combines
an autonomous classifier with LLM-assisted technical analysis and a
separate ActionableScore mechanism.
The purpose of this report is to prioritize Linux kernel CVEs before
manual review, identify cases that require prompt investigation, and
support automatic closure of issues that are unlikely to have meaningful
security impact.
Published priority for this report: IMPORTANT
Manual review required: YES
A detailed explanation of the methodology and priority rules is included
at the end of this message.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2026-98988 IMPORTANT https://www.kernelcve.org/list/?q=CVE-2026-98988 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=5 LEGACY=IMPORTANT RESULT=DIFF INDEPENDENT_LEGACY=IMPORTANT INDEPENDENT_RESULT=DIFF TEMP_KPANIC_MERGE=IMPORTANT_HARD_VETO PRE_MERGE_LEGACY=IMPORTANT (final Legacy and Aegis differ; FINAL: IMPORTANT, Aegis: MODERATE_KPANIC) Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N';*CWE-200;CWE-284;CWE-668;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N';BEST CVSS score: '5.5';DESCR 'OPEN_TREE_NAMESPACE could create a mount namespace from a foreign source while omitting child mounts in a non recursive copy or unbindable mounts in a recursive copy. This could reveal files and interfaces that container runtimes or administrators intentionally covered with mounts. For the CVSS the PR:L value is used because exploitation requires a local process and creation of a user namespace even though no privilege over the source mount namespace is needed. The demonstrated primitive is unauthorized content exposure. Normal file permission and LSM checks still apply, so integrity impact and privilege escalation are not established. The paranoid score uses C:H for deployments where mount masking protects sensitive readable content across a container or namespace boundary. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 5.5 and the production ActionableScore returned 7 with recommendation Strong Important candidate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage LOW to MODERATE_KPANIC because the manual review requirement was applied. ActionableScore thresholds stage MODERATE_KPANIC to IMPORTANT because the ActionableScore threshold rule was applied. final reconciliation stage IMPORTANT to IMPORTANT because a specific evidence based protection or manual review veto was applied and KP specialist did not establish a qualifying panic. The legacy KP specialist produced a review artifact and its decision was processed by the applicable KP rules. The legacy FD or DH downgrade specialist produced a review artifact and its decision was processed by the applicable downgrade and preservation rules. Exact triggered rule markers were INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK and INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHERTHAN5 and TEMP_KPANIC_MERGE_IMPORTANT_VETO and B4_CONFIRMED_AUTHORIZATION_PRESERVE and MANUAL_REVIEW_REQUIRED and KPANIC_UNSUPPORTED_REMOVED. The independent weaker Aegis shadow evaluated CVSS 3.3 and ActionableScore 5 with primitive class CLASS_A and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. Cross model aggregation changed the production result under an enabled evidence gated merge rule. The final reported impact is IMPORTANT.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate (with actual score 7) MAYBE LOCK DISK LINUS INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHERTHAN5 TEMP_KPANIC_MERGE_IMPORTANT_VETO B4_CONFIRMED_AUTHORIZATION_PRESERVE MANUAL_REVIEW_REQUIRED KPANIC_UNSUPPORTED_REMOVED - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=7
PrimitiveClass=CLASS_A
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=YES
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
RequiresHostUID0=NO
AuthorizationDecisionBypass=YES
ProtectedResourceImpact=CONFIRMED
B4PendingReview=YES
B4PendingConfirmed=YES
1. ActionableScore
* Raw base score: 7.
* Conservative score: 7; no floor or cap applied.
* Raw paranoid score: 7.
* Paranoid score: 7; no additional speculative impact counted.
* Final recommended bucket: **Strong Important candidate**::
2. Signal breakdown
* +2 Concrete authorization decision bypass: a foreign user namespace could request a non-recursive namespace copy that omitted covering child mounts; the fix changes this from success to `-EINVAL`.
* +2 Security-boundary bypass with practical protected-object access: the demonstrated `open_tree()`/`setns()` sequence reveals content intentionally hidden by a covering mount.
* +1 Local unprivileged trigger: the commit explicitly demonstrates UID 1000 creating a user namespace and invoking the interface without privilege over the source mount namespace.
* +1 Practical exploit chain: create user namespace → copy foreign mount tree incompletely → enter copied mount namespace → read the uncovered path.
* +1 Confidentiality plausible: actual hidden file content is read in the supplied example.
* No integrity, privilege escalation, memory corruption, kernel crash, arbitrary access, or bypass of ordinary DAC/LSM checks is shown. CVSS-style C:H is deployment-dependent and not independently assumed.
3. Reachability analysis
A normal local user can create a user namespace, thereby gaining the namespace-scoped privilege required for the newly owned mount namespace, while lacking authority over the source mount namespace. The complete demonstrated operation is therefore below host-admin and namespace-scoped. Unprivileged user-namespace availability is a deployment prerequisite; environments disabling it may block this path.
An administrator or container runtime must previously have installed the covering mount, but the attacker need not control that setup. No special hardware, race, or timing condition is involved.
4. Primitive and severity reading
The primitive is an authorization/isolation failure, not memory corruption. The missing foreign-source restrictions allowed creation of a mount namespace whose topology omitted mounts that enforce path masking. The concrete DENY-to-ALLOW path is:
`UID 1000 + new user namespace → open_tree(OPEN_TREE_NAMESPACE) on foreign mount namespace → incomplete clone succeeds instead of -EINVAL → setns() → covered file becomes visible`.
For recursive copies, adding `CL_COPY_UNBINDABLE` similarly preserves unbindable covering mounts. This is CLASS_A because it crosses an intended mount-namespace protection boundary and exposes a demonstrated protected resource. B4-PENDING is confirmed: the caller, below-host-admin credentials, protection decision, and covered resource are all grounded. ImportantCandidate is therefore YES and automatic downgrade is unsafe, although normal file permissions and LSM checks constrain final exposure.
5. One-sentence report phrase
An unprivileged user namespace could clone a foreign mount tree while omitting covering mounts, exposing administrator- or runtime-masked content that remained readable under ordinary DAC/LSM policy.
6. Manual review advice
MANUAL CHECK REQUIRED
Confirm affected product policy for unprivileged user namespaces and identify sensitive paths whose confidentiality relies on mount masking.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: namespace: keep covered mounts covered in OPEN_TREE_NAMESPACE
Commit: b8a94a405ddcf45e9470789e0a821d8f2aa4ca10
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b8a94a405ddcf45e9470789e0a821d8f2aa4ca10
Commit description:
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.
Fixes: 9b8a0ba ("mount: add OPEN_TREE_NAMESPACE")
Cc: [email protected] # v7.0+
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Christian Brauner (Amutable) <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
fs/namespace.c
Diff excerpt:
Not included in this email. See the upstream URL for the full patch.
Full patch:
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b8a94a405ddcf45e9470789e0a821d8f2aa4ca10
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98988 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98988
The original CVE announcement normally does not include a security-level
estimate. In particular, it may not contain a CVSS assessment, an impact
level, or enough information to determine whether the reported bug is a
practically relevant security issue. One purpose of this parallel CVE list
is to provide that missing technical and prioritization information.
The original goal of the AL-KERNEL project was to prioritize Linux kernel
CVE analysis automatically before manual review. The system can also help
identify non-security issues that may be suitable for automatic closure.
This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin.
The first analysis stage combines an autonomous classifier with additional
LLM-based analysis. The autonomous classifier runs locally on a CPU and is
based on a backpropagation neural network. Together, these mechanisms
produce a technical vulnerability description, identify likely weakness
types, estimate CVSS severity, and provide input for ActionableScore.
Two CVSS estimates are retained because incomplete kernel vulnerability
information often permits more than one defensible interpretation:
Conservative CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
The Best / paranoid CVSS score: 5.5
The conservative vector represents a lower-impact interpretation.
The Best/paranoid vector intentionally represents a plausible upper-bound
interpretation and should not automatically be treated as demonstrated
real-world impact.
CVSS may also need to be adjusted for a particular Linux deployment,
because actual reachability, privileges, enabled kernel configuration,
hardware, namespaces, exposed device nodes, and other environmental
conditions can differ significantly between systems.
A separate ActionableScore mechanism evaluates practical remediation
urgency. Its analysis may include reachability, attack prerequisites,
subsystem exposure, memory-corruption characteristics, denial-of-service
reliability, and possible confidentiality, integrity, or
privilege-escalation impact.
Conservative ActionableScore: unknown
Paranoid ActionableScore: 7
The final base severity is taken directly from the second tab-separated
field of the AL-KERNEL classification result. ActionableScore does not
replace or independently override that final AL-KERNEL decision, and
if ActionableScore adjusted impact level of ALKERNEL, then you would see
self-readable flags above like INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7.
For an AL-KERNEL result of MODERATE, this report uses the following
additional presentation split:
ActionableScore below 5 -> MODERATE REGULAR
ActionableScore 5 or more -> MODERATE 7.0
The distinction between MODERATE REGULAR and MODERATE 7.0 makes it
possible to identify Moderate issues that should receive manual analysis
and fixes before lower-priority MODERATE REGULAR issues. In many cases,
MODERATE REGULAR fixes may wait for a later rebase or routine update.
There is one override in which MODERATE REGULAR becomes MODERATE 7.0
even when the ActionableScore is below 5. When the AL-KERNEL result
contains the KPANIC flag, a MODERATE result is always presented as
MODERATE 7.0. The KPANIC flag selected with few regexps without
usage of AI at all, so it helps to detect cases when Kernel Crash happens
and similar (to filter False-Negative results from the LLM usage).
KPANIC indicates that a reliable kernel crash, kernel panic, or similarly
serious kernel availability impact was identified by the classification
workflow.
AL-KERNEL base severity for this report: IMPORTANT
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): IMPORTANT
These results are intended to support engineering triage. They are
machine-generated estimates, and cases marked for manual review should
be validated by a human security engineer before final disposition.
For more info read docs linked from here: https://kernelcve.org/
(and you can submit you own patch there to generate such a report
for non-existant CVE-id yet).
Note that in many cases this AI tool selects higher severity, than
real is (means you can expect Importants instead of Moderate 7.0 or
Moderates 7.0 instead of regular Moderates). If you see such cases,
please use reply email interface to add additional manual analyses
info to this particular CVE.
And please, please, let me know when you see Lows instead of Importants
or Important instead of Low (because particular for such cases I
need to tune this AI tool to make it better for this one and next similar).
My contact email for such notifications is [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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