* [CVE-2025-71182][MODERATE REGULAR] can: j1939: make j1939_session_activate() fail if device is no longer registered [ Upstream
@ 2026-09-20 4:20 21% AL-KERNEL
0 siblings, 0 replies; 1+ results
From: AL-KERNEL @ 2026-09-20 4:20 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2025-71182
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: can: j1939: make j1939_session_activate() fail if device is no longer registered [ Upstream
Commit: ebb0dfd718dd31c8d3600612ca4b7207ec3d923a
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ebb0dfd718dd31c8d3600612ca4b7207ec3d923a
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2025-71182
Analysis date: Sun, 20 Sep 2026 00:20:16 -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-2025-71182 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2025-71182
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: NO
A detailed explanation of the methodology and priority rules is included
at the end of this message.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2025-71182 MODERATE https://www.kernelcve.org/list/?q=CVE-2025-71182 CHECK WITH IMPACT FROM ORIG NN MODERATE 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:N/A:H';CWE-362;*CWE-664;CWE-667;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.7';DESCR 'A race condition in the CAN J1939 session lifecycle can allow j1939_session_activate to succeed after NETDEV_UNREGISTER has cancelled active sessions for the device. The new session can retain a reference to a netdevice that is being removed, causing unregister_netdevice to wait for the device usage count to drop and stalling removal of the CAN interface. For the CVSS the PR:L value is used because a local process needs access to the J1939 CAN interface and the required socket operations, while the unregister operation is normally performed by a local administrator or management service. The issue is not directly network reachable because CAN packet traffic alone does not perform device unregister or activate the relevant local control path. Impact is primarily denial of service affecting interface removal and network device management. No use after free invalid memory access information disclosure integrity impact or privilege escalation primitive is demonstrated by the patch context.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1) MAYBE DANGER INIT SIMPLEFIX RACE HARDWARE LINUS SYZBOT DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=1
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
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 Availability impact realistic. The demonstrated consequence is that `unregister_netdevice()` can wait indefinitely for the J1939 device reference count to drop. This can prevent removal of the affected CAN interface and block associated network-device management.
* +0 Real UAF. No object free, post-free dereference, second `put`, refcount mutation through freed storage, or stale-object access is established by the patch.
* +0 Kernel crash. The supplied evidence reports an unregister wait with usage count 2, not an Oops, panic, or host-wide crash.
* +0 Remote reachability. CAN/J1939 packet traffic does not itself execute the relevant netdevice unregister control path.
* +0 Local unprivileged trigger. The evidence does not establish that an ordinary unprivileged user can complete both the J1939 session activation and the required device-unregister sequence.
* +0 Strong or weak exploitation leverage. The race retains a netdevice reference and causes lifecycle blockage. It does not establish controlled replacement, memory corruption, invalid memory access, information disclosure, integrity impact, callback control, or privilege escalation.
* No race penalty applied. The patch establishes a race window, but the supplied evidence does not prove that it is unusually narrow, one-shot, externally uncontrollable, or hard to reproduce.
* No privilege penalty applied. The complete attacker privilege boundary is not established. The absence of proof of host-admin requirements is not proof of below-host-admin reachability.
3. Reachability analysis
The relevant sequence is a local control-plane lifecycle race: a J1939 session is activated while the associated CAN netdevice is being unregistered. The patch shows that `j1939_cancel_active_session()` may have completed, but `j1939_session_activate()` could still add a new active session before checking whether `priv->ndev` remains registered.
A local process must reach the J1939 session-activation path. A separate actor or operation must initiate `NETDEV_UNREGISTER`, for example through device removal, namespace teardown, or network-device management. The supplied material does not establish that one ordinary user can perform the complete sequence without elevated rights, nor does it establish that host-admin-equivalent privilege is necessarily required in all deployments.
`HostAdminRequired=UNKNOWN` is appropriate because the complete privilege boundary is unresolved. `NamespaceScopedPrivilege=UNKNOWN` is also appropriate because a CAN device can exist in a network namespace, but the evidence does not establish that all required operations, including creation or control of the relevant device and its unregister lifecycle, are reachable through attacker-controlled namespace-scoped capabilities.
No special hardware is required for the reported reproducer because it uses `vcan0`. However, the affected J1939 subsystem and the required device lifecycle race are not shown to be remotely reachable or generally reachable through ordinary application traffic.
4. Primitive and severity interpretation
The exact primitive is a lifecycle and synchronization failure. A J1939 session can be added to the active session list after the unregister notifier has cancelled sessions for a device. This can retain a device reference after unregister has started.
This is not an active structured-object UAF and not fixed stale storage. The supplied patch does not establish object destruction followed by use of freed memory. It also does not establish a concrete repeated `put`, `release`, `free`, or refcount mutation through the same potentially dangling reference.
The demonstrated consequence is an interface-unregister stall caused by a retained usage reference. The patch-supported practical impact is denial of service affecting removal and management of the affected CAN interface. A broader host-wide availability impact, confidentiality impact, integrity impact, privilege escalation, or memory-corruption primitive is speculative and is not scored.
`PrimitiveClass=CLASS_C` is appropriate because the established behavior is invalid lifecycle state and a device-unregister blockage without an independently useful corruption primitive. `ImportantCandidate=NO` is appropriate because no meaningful Important-class exploitation leverage remains unresolved. `AutoDowngradeAllowed=YES` is appropriate because the current evidence supports a constrained local availability issue rather than active kernel memory corruption, a security-boundary bypass, or a repeated lifetime mutation.
Likely operational severity is Low to ordinary Moderate. It may matter operationally on systems that dynamically create, remove, or reconfigure J1939 or virtual CAN devices, but it is not supported as an Important-class kernel security vulnerability.
5. One-sentence report phrase
A race in CAN J1939 session activation can retain a reference to a netdevice after unregister has started, causing `unregister_netdevice()` to stall and preventing removal of the affected CAN interface.
6. Manual review recommendation
MANUAL CHECK RECOMMENDED
Confirm the privilege requirements for J1939 session activation and netdevice unregister in the evaluated distribution and deployment model. The patch does not establish memory corruption, but actual operational impact may vary if CAN device lifecycle operations are delegated to containers, services, or non-host-admin network-management components.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: can: j1939: make j1939_session_activate() fail if device is no longer registered [ Upstream
Commit: ebb0dfd718dd31c8d3600612ca4b7207ec3d923a
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ebb0dfd718dd31c8d3600612ca4b7207ec3d923a
Changed files:
net/can/j1939/transport.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=ebb0dfd718dd31c8d3600612ca4b7207ec3d923a
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2025-71182 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2025-71182
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:L
The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
The Best / paranoid CVSS score: 4.7
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: 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).
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