From: AL-KERNEL <[email protected]>
To: [email protected]
Subject: [CVE-2026-89745][MODERATE 7.0] debugfs: Fix lockdown check for mmap_prepare
Date: Sat, 12 Sep 2026 01:36:40 -0400 [thread overview]
Message-ID: <[email protected]> (raw)
CVE: CVE-2026-89745
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: debugfs: Fix lockdown check for mmap_prepare
Commit: e7f6a6b5741d16fdac7adaecbe0fa52ae756f208
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e7f6a6b5741d16fdac7adaecbe0fa52ae756f208
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89745
Analysis date: Sat, 12 Sep 2026 01:36:40 -0400
ActionableScore: 5
ActionableScore lower bound: unknown
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES
Summary:
No one-sentence report phrase was found.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-89745 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89745
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.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2026-89745 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-89745 CHECK WITH IMPACT FROM ORIG NN MODERATE Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N';CWE-693;CWE-284;CWE-863;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:L/I:L/A:N';BEST CVSS score: '4.4';DESCR 'debugfs lockdown enforcement could be bypassed for files that implement mmap_prepare() but not mmap. The lockdown check only looked for mmap and ioctl handlers, so such files could avoid LOCKDOWN_DEBUGFS even when the kernel was running in integrity lockdown mode. This is a local security policy bypass rather than a memory corruption bug. For the CVSS the PR:L is used in the paranoid score because practical exposure may involve a local user, service account, container root, or delegated debugfs access rather than full unrestricted host administration. The issue is not network reachable and requires local access to an affected debugfs file. Impact is limited confidentiality or integrity policy impact through unintended debugfs mmap access, with no evidence of kernel memory corruption or direct privilege escalation.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5) SKIP CVE-2026-89745 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES NO NO unknown MAYBE READ DISK SIMPLEFIX IMPROVEONLY DEBUGFS DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS KPANIC INCREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN5 - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=5
PrimitiveClass=CLASS_A
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
1. ActionableScore
* Raw conservative score: 4
* Conservative score: 5
* Raw paranoid score: 5
* Paranoid score: 5
* Applied conservative floor/cap: CLASS_A authorization-bypass calibration 4 -> 5
* Applied paranoid floor/cap: none
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::
2. Signal breakdown
Positive signals:
* +2 Concrete authorization decision bypass. `debugfs_locked_down()` could incorrectly skip `security_locked_down(LOCKDOWN_DEBUGFS)` for debugfs files that implement `mmap_prepare()` but not `mmap`.
* +1 Central authorization helper fan-out. The patched helper is a debugfs lockdown gate for multiple file-operation classes, including ioctl-like and mmap-like access.
* +1 Externally meaningful access effect. Successful bypass permits a debugfs mmap-style operation that lockdown integrity mode intended to block.
* Paranoid +1 Limited confidentiality/integrity concern. Debugfs mmap access may expose or affect kernel debug surfaces depending on the specific file and permissions, but no concrete sensitive object or write primitive is established.
Non-awarded signals:
* RealUAF not awarded. No lifetime or stale-object bug is present.
* Controlled corruption not awarded. No UAF, OOB write, arbitrary write, or controlled reclaim exists in the patch.
* Privileged FD/resource theft not awarded. No downstream protected FD, credential, or file access chain is supplied.
* LPE not awarded. The evidence shows a lockdown policy bypass, not direct privilege escalation.
* Remote reachability not awarded. Trigger requires local access to debugfs.
* Host-admin penalty not applied. Host-admin-equivalent privilege is not positively established for every affected deployment.
* Namespace-scoped privilege not awarded. No evidence shows the complete operation is attacker-reachable inside namespaces.
3. Reachability analysis
The trigger is local access to an affected debugfs file whose real file operations include `mmap_prepare()` but not `mmap`. The kernel must be running in lockdown integrity mode, and the relevant debugfs file must be reachable with permissions that allow the attempted mmap path.
Host-admin-equivalent privilege is not proven from the supplied patch alone. Many debugfs deployments are root-only or administrator-controlled, but this is deployment policy, not a complete proof for all affected files. Below-host-admin reachability is also not fully established because the exact affected debugfs files and permissions are not enumerated. Therefore `HostAdminRequired=UNKNOWN`.
The operation is not network reachable. No race, timing window, special hardware, or memory-layout control is required. No namespace-scoped complete trigger is established.
4. Primitive and severity interpretation
The exact primitive is a kernel lockdown authorization bypass. The intended `LOCKDOWN_DEBUGFS` security check can be skipped for mmap-style debugfs access after the relayfs conversion to `mmap_prepare()`.
This is not memory corruption. It is not an active structured UAF, fixed stale storage, double release, or refcount mutation. The demonstrated consequence is unintended local debugfs mmap access while lockdown integrity mode expects denial. The practical impact depends on which debugfs `mmap_prepare()` files are present and accessible.
`PrimitiveClass=CLASS_A` because the patch directly restores a mandatory security-policy check whose absence changes an externally meaningful access-control result from deny to allow. `ImportantCandidate=YES` because kernel lockdown is a real security boundary and the downstream exposure is environment-dependent. `AutoDowngradeAllowed=NO` because automatically closing a lockdown-bypass issue could miss systems where accessible debugfs mmap surfaces expose sensitive kernel state or weaken integrity protections.
Likely operational severity is Actionable Moderate, with Strong Important review potential if a reachable debugfs `mmap_prepare()` file exposes sensitive data or integrity-relevant control.
5. One-sentence report phrase
A debugfs lockdown bypass allowed files using mmap_prepare() but not mmap to avoid LOCKDOWN_DEBUGFS checks in integrity lockdown mode, potentially permitting local debugfs mmap access that should have been denied.
6. Manual review recommendation
MANUAL CHECK REQUIRED
Reason: this is a concrete kernel security-boundary bypass, and real impact depends on the accessible debugfs files, their permissions, and whether their mmap_prepare path exposes sensitive kernel data or integrity-relevant state.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: debugfs: Fix lockdown check for mmap_prepare
Commit: e7f6a6b5741d16fdac7adaecbe0fa52ae756f208
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e7f6a6b5741d16fdac7adaecbe0fa52ae756f208
Commit description:
Commit 651fdda ("relay: update relay to use mmap_prepare")
changed the `mmap` file operation to `mmap_prepare` for relayfs, but
the lockdown check in debugfs was not updated accordingly.
This prevents debugfs from being locked down when the kernel is in
integrity mode if a file uses `mmap_prepare` but not `mmap`.
Since the conversion to `mmap_prepare` across the kernel is not yet
complete, update the lockdown check to look for both `mmap` and
`mmap_prepare` to ensure comprehensive coverage.
Fixes: 651fdda ("relay: update relay to use mmap_prepare")
Signed-off-by: Chun-Yi Lee <[email protected]>
Cc: David Howells <[email protected]>
Cc: Lorenzo Stoakes <[email protected]>
Cc: Andy Shevchenko <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Rafael J. Wysocki <[email protected]>
Cc: Matthew Garrett <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Cc: Danilo Krummrich <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Tested-by: Disha Goel <[email protected]>
Reviewed-by: Lorenzo Stoakes <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Danilo Krummrich <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
fs/debugfs/file.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=e7f6a6b5741d16fdac7adaecbe0fa52ae756f208
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-89745 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89745
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:H/UI:N/S:U/C:L/I:L/A:N
The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N
The Best / paranoid CVSS score: 4.4
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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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