* [CVE-2026-93210][LOW] smb: client: harden DFS cache against invalid target hints
@ 2026-09-24 17:34 21% AL-KERNEL
0 siblings, 0 replies; 1+ results
From: AL-KERNEL @ 2026-09-24 17:34 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-93210
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: smb: client: harden DFS cache against invalid target hints
Commit: a48328afbc3f63e3b9de8827e2e16c15b17976f7
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a48328afbc3f63e3b9de8827e2e16c15b17976f7
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93210
Analysis date: Thu, 24 Sep 2026 13:34:58 -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-2026-93210 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93210
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-2026-93210 LOW https://www.kernelcve.org/list/?q=CVE-2026-93210 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:N/I:N/A:H';**CWE-476;CWE-252;CWE-703;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.5';DESCR 'SMB DFS cache handling may dereference a NULL target hint or pass an ERR_PTR value to referral setup if a cached target hint is cleared while DFS cache data is being used. The resulting condition can cause a kernel NULL pointer dereference and local denial of service. This commit is explicitly preparatory for a later change that clears ce->tgthint and does not itself demonstrate a reachable trigger in the pre patch code. For the CVSS the PR:L reflects that a local user or process must cause access to an already configured SMB DFS mount and the relevant cache lifecycle. The issue is not directly network reachable from an unauthenticated SMB peer based on this patch alone. Confidentiality and integrity impact are not established.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1) YES NULLPTR DISK SIMPLEFIX SERVERTOCLIENT LINUS DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 NO NO checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=1
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
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**::
2. Signal breakdown
* +1 Reliable kernel crash or strong DoS. The patch explicitly prevents NULL pointer dereferences in DFS target-hint handling. Dereferencing `t->name` when `ce->tgthint` is NULL can cause an SMB client kernel Oops or crash.
* No remote reachability bonus. The patch does not establish that an unauthenticated remote SMB peer can independently create the required NULL target-hint state.
* No local unprivileged trigger bonus. The complete trigger requires an SMB DFS mount and a target-hint lifecycle state. The supplied patch does not establish that an ordinary local user can create the complete state without administrator-controlled mount setup.
* No UAF signal. The shown issue is a NULL target hint and unchecked `ERR_PTR(-ENOENT)` return. The patch does not establish that a freed object remains dereferenced through a dangling pointer.
* No repeated release or refcount mutation. No `put`, `release`, `free`, or refcount operation through a stale reference is shown.
* No controlled reclaim, arbitrary write, disclosure, integrity impact, authorization bypass, or privilege-escalation primitive is demonstrated.
* No race penalty. Although `READ_ONCE` is used and a later change may clear `ce->tgthint`, this patch alone does not establish a narrow timing race as the required trigger.
3. Reachability analysis
The vulnerable state is an SMB DFS cache entry whose `ce->tgthint` is NULL. The commit explicitly says it is preparation for a later change in `free_tgts()` that clears this field. Therefore, the shown pre-patch code does not itself demonstrate that the NULL state is reachable in the affected version without the associated later lifecycle change.
Access to the affected paths requires use of the SMB client DFS cache, normally through an existing SMB DFS mount and referral lookup activity. The patch does not identify the capability checks for mount creation, DFS cache administration, or the complete target-hint clearing path. Host-admin-equivalent privilege is therefore `UNKNOWN`, not assumed. Namespace-scoped privilege is also `UNKNOWN` because no complete namespace-scoped trigger chain is shown.
There is no special hardware requirement. Remote reachability is not established merely because SMB is a network filesystem. A remote server may influence referrals after an SMB DFS client mount exists, but the supplied evidence does not prove that a remote peer can cause `ce->tgthint` to become NULL and then reach the dereference without a local lifecycle condition.
4. Primitive and severity interpretation
The concrete primitive is an invalid-state NULL pointer dereference and unchecked error-pointer propagation. `get_tgt_name()` can return `ERR_PTR(-ENOENT)` when `ce->tgthint` is NULL, while the old callers passed its result directly to `setup_referral()`. Separately, `dfs_cache_noreq_update_tgthint()` accessed `t->name` without verifying that the `READ_ONCE()` result was non-NULL.
This is not an active structured-object UAF. The patch protects against a NULL pointer after the target hint is cleared, not use of a freed target object through a surviving dangling reference. No second lifetime mutation, controlled replacement, callback consumption, attacker-controlled post-free state, arbitrary read or write, confidentiality impact, integrity impact, or privilege escalation is established.
The demonstrated practical consequence is at most a local kernel Oops or denial of service when the required cache state is reachable. The later `free_tgts()` behavior referenced in the commit should be reviewed together with this patch if a CVE is assigned to the complete patch series, but this hardening commit alone does not establish Important-class exploitation leverage.
`ImportantCandidate=NO` because there is no Class A or Class B lifetime/corruption primitive. `AutoDowngradeAllowed=YES` because the demonstrated issue is a constrained NULL dereference without unresolved post-lifetime corruption or security-boundary behavior.
5. One-sentence report phrase
An SMB DFS cache target hint can be NULL or represented by an unchecked ERR_PTR result, potentially causing a local kernel NULL pointer dereference and denial of service when the relevant DFS cache lifecycle state is reached.
6. Manual review recommendation
NO MANUAL CHECK NEEDED
The commit is explicitly preparatory for a later target-hint clearing change and establishes only NULL-pointer and error-return hardening, without a concrete UAF, memory-corruption, authorization-bypass, remote-trigger, or privilege-escalation primitive.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: smb: client: harden DFS cache against invalid target hints
Commit: a48328afbc3f63e3b9de8827e2e16c15b17976f7
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a48328afbc3f63e3b9de8827e2e16c15b17976f7
Commit description:
Currently, get_tgt_name() returns ERR_PTR(-ENOENT) when ce->tgthint is
NULL, and dfs_cache_noreq_update_tgthint() assumes ce->tgthint is always
valid.
In preparation for clearing ce->tgthint in free_tgts(), harden callers
of get_tgt_name() against ERR_PTR results and harden
dfs_cache_noreq_update_tgthint() against NULL pointer dereferences.
Cc: [email protected]
Signed-off-by: Fredric Cover <[email protected]>
Reviewed-by: ChenXiaoSong <[email protected]>
Signed-off-by: Namjae Jeon <[email protected]>
Signed-off-by: Paulo Alcantara <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
fs/smb/client/dfs_cache.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=a48328afbc3f63e3b9de8827e2e16c15b17976f7
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-93210 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93210
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:N/A:H
The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
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: 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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