* [CVE-2026-90055][LOW] usb: atm: usbatm: fix invalid ci_range initialization [ Upstream
@ 2026-09-18 2:23 21% AL-KERNEL
0 siblings, 0 replies; 1+ results
From: AL-KERNEL @ 2026-09-18 2:23 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-90055
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: usb: atm: usbatm: fix invalid ci_range initialization [ Upstream
Commit: 8442586526c406527bf31206e538c0ce6bc672e6
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8442586526c406527bf31206e538c0ce6bc672e6
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90055
Analysis date: Thu, 17 Sep 2026 22:23:14 -0400
ActionableScore: 1
ActionableScore lower bound: 0
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-2026-90055 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90055
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-2026-90055 LOW https://www.kernelcve.org/list/?q=CVE-2026-90055 CHECK WITH IMPACT FROM ORIG NN LOW 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-665;CWE-682;CWE-758;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.5';DESCR 'A shift out of bounds bug in the USB ATM usbatm path occurs because ci_range.vpi_bits and ci_range.vci_bits were initialized with ATM_CI_MAX, which is -1 and not a valid bit count. The ATM connect path later uses these fields as shift counts in __vcc_connect, so a local bind operation can trigger a negative shift and a UBSAN warning. For the CVSS the PR:L reflects the paranoid scenario where a local user or service has delegated network administration capability or access to ATM socket operations on a system with a USB ATM device. The issue is not directly network reachable and does not show a concrete UAF, OOB write, or arbitrary write primitive. Impact is mainly denial of service, with high availability impact only in configurations where UBSAN or warning handling can panic the kernel.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1) YES WRITE KASAN OOB USB HARDWARE LINUS SYZBOT 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
ActionableScoreLower=0
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES
1. ActionableScore
* Raw conservative score: 0
* Conservative score: 0. No floor or cap applied.
* Raw paranoid score: 1
* Paranoid score: 1. No floor or cap applied.
* Final recommended bucket: **Ordinary Moderate**::
2. Signal breakdown
Conservative signals:
* +1 CLASS_C invalid-state arithmetic bug. usbatm initializes ci_range.vpi_bits and ci_range.vci_bits to ATM_CI_MAX, which is -1, and the ATM connect path later uses these values as shift counts.
* -1 specialized and difficult-to-reach device path. The affected state is created by the USB ATM driver, so practical triggering requires a USB ATM device or equivalent emulated/fuzzed device environment.
* +0 reliable kernel crash not awarded. The supplied evidence shows a UBSAN shift-out-of-bounds warning, not an unconditional panic.
* +0 local unprivileged trigger not awarded. The stack shows a local bind path, but complete below-host-admin reachability for the needed ATM device/socket operation is not established.
* +0 C/I not awarded. No UAF, OOB write, arbitrary write, disclosure, authorization bypass, or ownership violation is established.
Paranoid signals:
* +1 same CLASS_C invalid-state arithmetic bug.
* +1 potential DoS in stricter debug or production-hardening configurations. If UBSAN or warning handling is configured to panic, the warning can become a kernel crash.
* -1 specialized USB ATM device path.
* No additional paranoid corruption point awarded. Undefined shift here is caused by an invalid bit-count sentinel and does not establish memory corruption.
Important non-awarded signals:
* Controlled reclaim not demonstrated.
* Arbitrary write not demonstrated.
* Real UAF not demonstrated.
* Concrete repeated release/refcount mutation not present.
* Remote reachability not established.
* Extra Availability not awarded because the only stronger consequence is the same warning becoming fatal under specific policy.
* Confidentiality and integrity not awarded because there is no disclosure or unauthorized modification primitive.
3. Reachability analysis
The visible trigger is local: an ATM PVC bind path reaches pvc_bind, vcc_connect, and then __vcc_connect where ci_range fields are used as shift counts. The vulnerable ci_range values are initialized by usbatm_atm_init, so an affected USB ATM device must exist or be emulated in the environment.
Host-admin-equivalent privilege is not positively established from the supplied input, but below-host-admin reachability is also not proven. Therefore HostAdminRequired is UNKNOWN. No evidence shows that the complete trigger chain is namespace-scoped, so NamespaceScopedPrivilege is UNKNOWN.
There is no direct network packet-processing trigger. This is not a race. The main practical prerequisite is the presence of the USB ATM device path, which is specialized and not broadly deployed.
4. Primitive and severity interpretation
The exact primitive is an invalid initialization of ATM connection range bit counts. A sentinel value, ATM_CI_MAX equal to -1, is stored where a valid shift count is required. Later code interprets that value as a shift exponent, causing shift-out-of-bounds undefined behavior and a UBSAN warning.
This is not active structured-object UAF and not fixed stale storage. No concrete repeated release/refcount operation exists. The demonstrated consequence is a local warning, with possible DoS only if warning or UBSAN handling is fatal.
PrimitiveClass is CLASS_C because the behavior is invalid-state or warning/DoS oriented without an independently useful corruption primitive. ImportantCandidate is NO because there is no memory corruption, ownership violation, authorization bypass, or unresolved lifetime primitive. AutoDowngradeAllowed is YES because the issue is suitable for ordinary low-priority handling unless a product specifically treats UBSAN warnings as fatal on systems with USB ATM exposure.
5. One-sentence report phrase
USB ATM initialized ATM VPI and VCI bit-count fields with the invalid -1 ATM_CI_MAX sentinel, allowing a local ATM bind path to trigger a negative shift in __vcc_connect and at most a warning-driven denial of service on affected configurations.
6. Manual review recommendation
NO MANUAL CHECK NEEDED
Reason: no UAF, memory corruption, privilege escalation path, authorization bypass, or remote trigger is established, and the issue is limited to a specialized USB ATM local path with warning or debug-policy DoS impact.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: usb: atm: usbatm: fix invalid ci_range initialization [ Upstream
Commit: 8442586526c406527bf31206e538c0ce6bc672e6
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8442586526c406527bf31206e538c0ce6bc672e6
Changed files:
net/atm/common.c
lib/dump_stack.c
lib/ubsan.c
net/atm/pvc.c
net/socket.c
drivers/usb/atm/usbatm.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=8442586526c406527bf31206e538c0ce6bc672e6
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-90055 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90055
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:N/I:N/A:L
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: 0
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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