[CVE-2026-98977][MODERATE 7.0] namespace: handle mount locking for automounts correctly [ Upstream

[AL-KERNEL <alkernel@kernelcve.org>]

CVE: CVE-2026-98977
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: namespace: handle mount locking for automounts correctly [ Upstream
Commit: 5e8f3ac8fa3d411b422ad32b9168c46a4824cc79
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5e8f3ac8fa3d411b422ad32b9168c46a4824cc79
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98977
Analysis date: Mon, 26 Oct 2026 14:28:16 -0400
ActionableScore: 5
ActionableScore lower bound: unknown
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
An unprivileged namespace task can trigger a propagated automount whose lock is assigned to the host copy, allowing the task to clear protected mount flags while preventing host administration of its own mount.

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ABOUT THIS REPORT
======================================================================

The original Linux kernel CVE announcement for CVE-2026-98977 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98977

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: MODERATE 7.0
Manual review required: YES

A detailed explanation of the methodology and priority rules is included
at the end of this message.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-98977	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98977 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=3 LEGACY=MODERATE_KPANIC RESULT=SAME (final reconciliation agrees; DECISION: both MODERATE_KPANIC)	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:L';CWE-284;CWE-266;CWE-863;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:C/C:L/I:L/A:L';BEST CVSS score: '6.3';DESCR 'attach_recursive_mnt used the callers user namespace even when an automount was actually attached to a mount in another namespace. This could lock the host copy while leaving the copy propagated into an unprivileged namespace unlocked. The demonstrated result allows the child to clear mount restrictions while the host receives EPERM when changing its own mount. For the CVSS the PR:L value reflects that an unprivileged local process must create or enter user and mount namespaces and trigger path lookup through an available directory descriptor. The issue is not directly network reachable and requires shared mount propagation plus an automount configuration. Low confidentiality and integrity impact is plausible because missing mount locks can permit removal of an overmount that hides underlying paths or weakening of nosuid, nodev, and noexec restrictions. Availability impact is limited to impaired administration of affected host mounts. There is no evidence of UAF, out of bounds access, arbitrary memory writes, or direct host privilege escalation. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 6.3 and the production ActionableScore returned 5 with recommendation Actionable Moderate / Strong Important candidate requiring manual review. 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. 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 has no review artifact for this run. Exact triggered rule markers were INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK. The independent weaker Aegis shadow evaluated CVSS 3.8 and ActionableScore 3 with primitive class CLASS_C and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. The shadow agreed with the final production impact and aggregation did not change that impact. The final reported impact is MODERATE_KPANIC.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5)	MAYBE	LOCK DISK IMPROVEONLY DEBUGFS LINUS  KPANIC INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK	-	-	checked

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ACTIONABLESCORE ANALYSIS
======================================================================

ActionableScore=5
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: 5.
* Conservative score: 5; no floor or cap applied.
* Raw paranoid score: 5.
* Paranoid score: 5.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

2. Signal breakdown

* +2 Concrete authorization decision bypass: using the caller’s user namespace assigns the mount lock to the wrong propagated copy. The child’s bind remount succeeds where the intended lock should produce `EPERM`.
* +1 Local unprivileged trigger: the commit explicitly grounds a child in unprivileged user and mount namespaces triggering lookup through an available directory descriptor.
* +1 Practical chain: path lookup triggers the host automount, propagation creates the child copy, incorrect ownership leaves that copy unlocked, and `MS_REMOUNT|MS_BIND` succeeds.
* +1 Integrity impact: the child demonstrably clears `nosuid,nodev,noexec` restrictions on its propagated mount copy.
* +1 Availability/administration impact: the host copy is incorrectly locked and the host receives `EPERM` when changing its own mount flags.
* -1 Unusual, host-provisioned topology: exploitation requires a shared host mount, a pending automount, propagation into the child namespace, and a directory descriptor supplied or inherited from that mount.

No memory corruption, UAF, arbitrary write, protected-file overwrite, credential change, host privilege escalation, or confidentiality disclosure is shown. No extra boundary-bypass point is added because that would duplicate the authorization primitive.

3. Reachability analysis

The evidenced actor is a below-host-admin child able to enter user and mount namespaces. The complete demonstrated child-side operations are namespace-scoped, including lookup and bind remount. Host preparation is required: the shared mount, automount, and usable directory descriptor must already exist. No special hardware or timing race is involved.

4. Primitive and severity reading

The primitive is an active mount-policy ownership error: `attach_recursive_mnt()` derives locking authority from the caller’s namespace rather than the namespace receiving the automount. The resulting state is consumed by later remount authorization, producing a concrete DENY-to-ALLOW transition for the child and an erroneous denial for the host.

The confirmed B4 path is:

unprivileged child lookup through inherited/handed directory FD → automount attached in host mount namespace → wrong user namespace used for locking → child’s propagated copy remains unlocked → child bind-remount succeeds instead of returning `EPERM`.

This is CLASS_A authorization/policy bypass, not memory corruption. ImportantCandidate is YES because protected mount restrictions cross a user-namespace boundary and are demonstrably weakened. Auto-downgrade is disallowed, although LPE and access to underlying protected content remain unproven.

5. One-sentence report phrase

An unprivileged namespace task can trigger a propagated automount whose lock is assigned to the host copy, allowing the task to clear protected mount flags while preventing host administration of its own mount.

6. Manual review advice

MANUAL CHECK REQUIRED

B4-PENDING is confirmed by a concrete below-host-admin DENY-to-ALLOW remount path affecting protected mount-policy state.

7. Call-site confidence

Call-site confidence: high

======================================================================
UPSTREAM PATCH SUMMARY
======================================================================

Patch: namespace: handle mount locking for automounts correctly [ Upstream
Commit: 5e8f3ac8fa3d411b422ad32b9168c46a4824cc79
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5e8f3ac8fa3d411b422ad32b9168c46a4824cc79

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=5e8f3ac8fa3d411b422ad32b9168c46a4824cc79

======================================================================
DETAILED REPORT METHODOLOGY
======================================================================

The original Linux kernel CVE announcement for CVE-2026-98977 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98977

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:H/PR:L/UI:N/S:C/C:L/I:L/A:L
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:L
  The Best / paranoid CVSS score: 6.3

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: 5

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: MODERATE
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): MODERATE 7.0

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 alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).