* [CVE-2026-98127][LOW] smb/client: validate new EOF for insert range [ Upstream
@ 2026-09-25 16:33 21% AL-KERNEL
0 siblings, 0 replies; 1+ results
From: AL-KERNEL @ 2026-09-25 16:33 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-98127
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: smb/client: validate new EOF for insert range [ Upstream
Commit: 7c2c69045aa76ccaa7f16f1478eb312130ce4951
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=7c2c69045aa76ccaa7f16f1478eb312130ce4951
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98127
Analysis date: Fri, 25 Sep 2026 12:33:47 -0400
ActionableScore: 1
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO
Summary:
No one-sentence report phrase was found.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98127 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98127
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: LOW
Manual review required: NO
A detailed explanation of the methodology and priority rules is included
at the end of this message.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2026-98127 LOW https://www.kernelcve.org/list/?q=CVE-2026-98127 CHECK WITH IMPACT FROM ORIG NN LOW Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:H';CWE-693;CWE-190;*CWE-20;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:L';BEST CVSS score: '5.3';DESCR 'The SMB client smb3_insert_range path did not validate the resulting EOF before increasing the file size. A local user with write access to a file on a CIFS SMB mount could use FALLOC_FL_INSERT_RANGE to bypass RLIMIT_FSIZE, exceed the filesystem maximum file size, or trigger an invalid loff_t size calculation. For the CVSS the PR:L is selected because the attacker needs local code execution and permission to modify a file on the mounted share. The issue is not directly network reachable because it is triggered through a local fallocate operation, although a compatible remote SMB server and an SMB3 mount are required. Impact is a file size policy bypass and possible resource exhaustion. There is no evidence in the patch of kernel memory corruption, privilege escalation, or direct confidentiality impact.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1) YES DISK IMPROVEONLY SERVERTOCLIENT LINUS DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 YES NO checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=1
PrimitiveClass=NONE
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES
1. ActionableScore
* Raw conservative score: 1
* Conservative score: 1
* Raw paranoid score: 1
* Paranoid score: 1
* Final recommended bucket: **Ordinary Moderate**::
No floor or cap was applied.
2. Signal breakdown
* +1 Local unprivileged trigger. A local non-administrative user who already has write access to a file on an existing writable CIFS SMB mount can invoke fallocate with FALLOC_FL_INSERT_RANGE.
* +0 Memory corruption. The patch establishes missing EOF validation and unchecked arithmetic, but does not establish an OOB access, UAF, invalid kernel pointer use, arbitrary write, or filesystem metadata corruption.
* +0 Integrity impact. The caller already needs permission to modify the affected file. Bypassing RLIMIT_FSIZE changes enforcement of a per-process file-size limit but does not by itself establish unauthorized modification of another principals data or protected kernel state.
* +0 Strong resource exhaustion. Repeated operations could grow a file beyond RLIMIT_FSIZE, but filesystem quotas, SMB server quotas, free-space limits, and ordinary write permissions remain applicable. Host-wide exhaustion or isolation bypass is not established.
* +0 Remote reachability. The vulnerable operation is a local fallocate call. A remote SMB server is a deployment prerequisite, not a direct remote attacker trigger.
* +0 Privilege escalation. No authorization bypass affecting another principal, protected resource access, credential modification, or LPE path is established.
* +0 Confidentiality. No disclosure or read-back primitive is established.
3. Reachability analysis
The triggering actor is a local process that can open a writable file on an already mounted CIFS SMB share and call fallocate with FALLOC_FL_INSERT_RANGE. This does not require host-admin-equivalent privilege after the mount and writable file access already exist, so HostAdminRequired is NO.
A host administrator may have mounted the SMB filesystem or provisioned the share, but that is ordinary prior deployment setup and is not required for the local attacker to invoke the vulnerable operation against a file they can write. No namespace-specific capability check is identified. The relevant access control is normal VFS and SMB file write permission, not a complete namespace-scoped privilege chain.
No special hardware, race, privileged device management, or unusual timing condition is required. The SMB server must support the relevant SMB3 insert-range operation, which limits exposure but does not create a memory-corruption or security-boundary primitive.
4. Primitive and severity interpretation
The exact defect is missing validation of the new EOF in smb3_insert_range. Before the fix, old_eof plus len could bypass inode_newsize_ok checks, including RLIMIT_FSIZE and maximum file-size validation, and could overflow or exceed the valid loff_t range.
This is a validation and file-size-policy enforcement issue. It is not an active-object lifetime defect, UAF, double release, stale reference, OOB access, or filesystem ownership and COW violation. The patch adds check_add_overflow and inode_newsize_ok before modifying the file.
The demonstrated consequence is that a process can exceed its RLIMIT_FSIZE through FALLOC_FL_INSERT_RANGE even though ordinary writes are stopped by the same limit. The potentially broader consequence is additional local resource use if independent quota and free-space controls do not stop the operation. Neither kernel memory corruption nor a cross-user or cross-container security-boundary bypass is established.
PrimitiveClass is NONE. ImportantCandidate is NO because the defect does not leave unresolved corruption, ownership, lifetime, or authorization leverage. AutoDowngradeAllowed is YES because the supplied patch supports a constrained local validation failure with no demonstrated escalation primitive.
5. One-sentence report phrase
A local user with write access to a file on a CIFS SMB mount could bypass RLIMIT_FSIZE through FALLOC_FL_INSERT_RANGE because smb3_insert_range did not validate the resulting EOF, potentially allowing unintended file growth but without demonstrated kernel memory corruption or privilege escalation.
6. Manual review recommendation
NO MANUAL CHECK NEEDED
The patch establishes a local file-size validation bypass and possible limited resource-consumption effect, but no concrete memory-corruption, lifetime, cross-ownership, authorization-bypass, or privilege-escalation primitive.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: smb/client: validate new EOF for insert range [ Upstream
Commit: 7c2c69045aa76ccaa7f16f1478eb312130ce4951
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=7c2c69045aa76ccaa7f16f1478eb312130ce4951
Changed files:
fs/smb/client/smb2ops.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=7c2c69045aa76ccaa7f16f1478eb312130ce4951
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98127 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98127
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:U/C:N/I:L/A:L
The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:H
The Best / paranoid CVSS score: 5.3
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: 1
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: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW
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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