* [CVE-2026-99137][MODERATE REGULAR] cifs: don't update i_size in cifs_do_truncate without a cached handle
@ 2026-10-30 16:16 21% AL-KERNEL
0 siblings, 0 replies; 1+ results
From: AL-KERNEL @ 2026-10-30 16:16 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-99137
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: cifs: don't update i_size in cifs_do_truncate without a cached handle
Commit: 04d020b3d0b58a1b7e116900e4095b96a7f4e11a
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=04d020b3d0b58a1b7e116900e4095b96a7f4e11a
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99137
Analysis date: Fri, 30 Oct 2026 12:16:13 -0400
ActionableScore: 3
ActionableScore lower bound: unknown
Actionable bucket: Borderline / manual review recommended
Manual review required: YES
Summary:
A permitted CIFS truncate can desynchronize local inode size from server state and leave stale cached data available after later file extension.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-99137 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99137
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 REGULAR
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-2026-99137 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-99137 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=1 LEGACY=MODERATE RESULT=DIFF (final Legacy and Aegis differ; FINAL: MODERATE, Aegis: MODERATE_KPANIC) Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:L';CWE-436;CWE-524;*CWE-664;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:L';BEST CVSS score: '4.5';DESCR 'A CIFS O_TRUNC operation lacking a cached writable handle could report success from cifs_file_flush without sending set_file_size to the server. The client could then set the local inode size to zero even though the server file remained unchanged, and a later failed cifs_open would leave inconsistent client and server state. Stale cached pages could also survive and be served after the file is later extended, creating a plausible low impact stale data exposure or integrity issue. For the CVSS the PR:L value is selected because reliable triggering requires a local process with access to the mounted SMB share and permission to perform the relevant file operation. AC:H reflects the required no handle state, the later open failure, and cache state. This is a logic and cache coherency flaw with no supported kernel memory corruption or privilege escalation primitive. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 4.5 and the production ActionableScore returned 3 with recommendation Borderline / manual review recommended. 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 MODERATE because the ActionableScore threshold rule was applied. The legacy KP specialist has no review artifact for this run. 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 and DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 and V41_INHERITED_KPANIC_PROMOTION_BLOCKED and MANUAL_REVIEW_REQUIRED. The independent weaker Aegis shadow evaluated CVSS 2.6 and ActionableScore 1 with primitive class CLASS_C and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. The models disagreed but the aggregation rules retained the production result. The final reported impact is MODERATE.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 3) MAYBE DISK LEAK SERVERTOCLIENT LINUS INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 V41_INHERITED_KPANIC_PROMOTION_BLOCKED MANUAL_REVIEW_REQUIRED - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=3
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
RequiresHostUID0=NO
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO
1. ActionableScore
* Raw base score: 3.
* Conservative score: 3; no floor or cap applied.
* Raw paranoid score: 3.
* Paranoid score: 3; stronger corruption or protected-resource impact is unsupported.
* Final recommended bucket: **Borderline / manual review recommended**::
2. Signal breakdown
* +1 Local unprivileged trigger: a process with access to the mounted share and permission to truncate the file can reach the operation; host administration is not required.
* +1 Confidentiality plausible: the patch explicitly evicts stale pages because otherwise they can be served after the server file is later extended.
* +1 Important filesystem/storage path: CIFS inode size and page-cache coherency diverge from authoritative server state.
* No race penalty: the required no-handle, failed-open, and cache sequence raises complexity but is not shown to require a narrow uncontrollable race.
* No memory-corruption, UAF, OOB-write, authorization-bypass, COW-ownership, or protected-file overwrite primitive is shown.
* No separate integrity point: setting the local inode size incorrectly is real state inconsistency, but unauthorized modification of protected server data is not established.
* B5-R does not apply: there is no retry-accumulated heap OOB write or corrupted descriptor consumption.
* B3-PENDING does not apply: stale cache pages remain readable, but no write to shared/file-backed backing storage is shown.
3. Reachability analysis
The complete trigger is available to a local process already authorized to access and truncate the CIFS file. No host UID 0, capability, namespace privilege, special hardware, or separate privileged setup is evidenced. Trigger reliability depends on lacking a cached writable handle, subsequent open failure, and suitable cache history, but these are state preconditions rather than a proven hard race.
4. Primitive and severity reading
The primitive is a filesystem cache-coherency and inode-state error: local `i_size` can become zero while the server file remains unchanged, and stale cached pages can survive for later delivery. This is CLASS_C invalid-state behavior, not kernel memory corruption. Low-impact stale-data disclosure is plausible; cross-user disclosure, persistent server-file corruption, privilege escalation, and host crash are unproven. ImportantCandidate is therefore NO, and automatic Important-to-Moderate downgrade is allowed.
5. One-sentence report phrase
A permitted CIFS truncate can desynchronize local inode size from server state and leave stale cached data available after later file extension.
6. Manual review advice
MANUAL CHECK RECOMMENDED
Confirm whether stale pages can be returned across a meaningful user or credential boundary in the affected CIFS deployment.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: cifs: don't update i_size in cifs_do_truncate without a cached handle
Commit: 04d020b3d0b58a1b7e116900e4095b96a7f4e11a
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=04d020b3d0b58a1b7e116900e4095b96a7f4e11a
Commit description:
If find_writable_file() returns null, cifs_file_flush will return
0 without issuing set_file_size, and the outer 'if (!rc)' block
will set i_size to 0 before telling the server to truncate. If
the cifs_open() then fails, the inode will have size 0, while
the server file is unchanged.
Move the netfs_resize_file() and cifs_setsize() into the 'if
(cfile)', so they only run after a successful set_file_size.
In the no-handle else branch, evict stale pages with
truncate_inode_pages before the O_TRUNC open to dispose of old
cache pages, and let the open response set the i_size.
Fixes: 110fee6 ("smb: client: fix missing timestamp updates with O_TRUNC")
Cc: [email protected]
Signed-off-by: Frank Sorenson <[email protected]>
Acked-by: David Howells <[email protected]>
Signed-off-by: Paulo Alcantara <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
fs/smb/client/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=04d020b3d0b58a1b7e116900e4095b96a7f4e11a
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-99137 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99137
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:L/I:L/A:L
The Best / paranoid CVSS score: 4.5
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: 3
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: NO
Published priority for this report (same as in Subject): MODERATE REGULAR
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).
^ permalink raw reply [relevance 21%]
Results 1-1 of 1 | reverse | sort options + mbox downloads above
-- links below jump to the message on this page --
2026-10-30 16:16 21% [CVE-2026-99137][MODERATE REGULAR] cifs: don't update i_size in cifs_do_truncate without a cached handle AL-KERNEL
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox