[CVE-2026-90057][MODERATE 7.0] slip: remove slip_hangup() to fix use-after-free in slip_receive_buf() [ Upstream

[AL-KERNEL <alkernel@kernelcve.org>]

CVE: CVE-2026-90057
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: slip: remove slip_hangup() to fix use-after-free in slip_receive_buf() [ Upstream
Commit: 9a3b1edff1ecb47d323f2506b3ffc22178acd1c6
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9a3b1edff1ecb47d323f2506b3ffc22178acd1c6
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90057
Analysis date: Fri, 18 Sep 2026 02:08:47 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
No one-sentence report phrase was found.

======================================================================
ABOUT THIS REPORT
======================================================================

The original Linux kernel CVE announcement for CVE-2026-90057 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90057

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 7.0
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-2026-90057	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-90057 CHECK WITH IMPACT FROM ORIG NN IMPORTANT	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-362;CWE-667;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A use-after-free in the SLIP line discipline can occur because slip_hangup calls slip_close while tty hangup processing only holds a read lock on tty ldisc_sem. slip_close unregisters and frees the net device and private struct slip while slip_receive_buf or another reader can still run and dereference the freed object. For the CVSS the PR:L is used for the paranoid score because a local user or constrained service with access to an already configured SLIP tty may be able to race receive_buf against hangup, although creating the SLIP line discipline commonly requires CAP_NET_ADMIN. The issue is not directly network reachable and is triggered through local tty line discipline activity rather than remote packet traffic. Impact is at least local denial of service via kernel crash. In the worst defensible case, the kernel UAF may allow confidentiality or integrity impact and should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5)	YES	UAF NETWORK HARDWARE LINUS KPANIC  KPANIC DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN6	NO	NO	checked

======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================

ActionableScore=5
ActionableScoreLower=4
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO

1. ActionableScore

* Raw conservative score: 3
* Conservative score: 4
* Raw paranoid score: 4
* Paranoid score: 5
* Conservative floor applied: 3 -> 4 due to real active-object UAF with host-admin-equivalent reachability not positively established.
* Paranoid floor applied: 4 -> 5 due to active receive-path stale-object use beyond ordinary cleanup-only fault behavior.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

2. Signal breakdown

Conservative positive signals:

* +2 Real UAF / active lifetime violation. The commit directly establishes that slip_close() unregisters and frees the net device and private struct slip while slip_receive_buf() may concurrently dereference freed memory.
* +1 Reliable kernel crash / strong DoS. The reported slab-use-after-free read is a realistic kernel fault or crash condition.

Conservative negative signals:

* No privilege penalty applied. SLIP setup commonly requires CAP_NET_ADMIN, but the supplied evidence does not positively establish that host-admin-equivalent privilege is required for the complete vulnerable race once a SLIP tty exists.
* No race penalty applied. The bug is a race against tty hangup, but the supplied evidence does not prove that the timing is one-shot, externally uncontrollable, or unusually hard to repeat.

Paranoid additional signal:

* +1 Active structured receive-path concern. The stale object is not only touched in a destructor path. It is consumed by slip_receive_buf(), a live line-discipline receive path, leaving meaningful exploitation analysis unresolved even though controlled reclaim is not demonstrated.

Important non-awarded signals:

* Controlled reclaim not demonstrated.
* Arbitrary read or arbitrary write not demonstrated.
* Callback or function-pointer control not demonstrated.
* Concrete repeated release/refcount mutation not established.
* Structured stale-object leverage beyond the active receive-path concern is not separately awarded.
* Weak LPE is not separately awarded because there is no concrete reuse, replacement, or controlled post-free object evidence.
* C/I Actionable bonuses are not awarded merely because a UAF could theoretically corrupt reclaimed memory.
* Extra Availability is not awarded because the same crash is already counted.
* Remote reachability is not established. This is tty line-discipline activity, not direct packet-processing exposure.

Repeated-release/refcount checklist:

* First release can end lifetime: yes, slip_close() can unregister/free the net device and private struct slip.
* Exact same reference survives to a second lifetime mutation: not established.
* Second operation is a real lifetime/refcount mutation: not established.
* +1 Concrete repeated release/refcount awarded: no.
* Paranoid repeated-refcount leverage +1 awarded: no.
* FLOOR 5 applied: yes, but due to active receive-path stale-object use, not due to repeated release/refcount.

3. Reachability analysis

The trigger is local tty line-discipline activity racing receive_buf processing against tty hangup. A remote network packet path is not established.

The complete privilege boundary is unresolved from the supplied patch alone. Creating or opening SLIP line discipline instances commonly involves administrative networking privilege such as CAP_NET_ADMIN, but the input also leaves open a scenario where a less privileged local user or constrained service can interact with an already configured SLIP tty and trigger hangup/receive concurrency. Therefore HostAdminRequired is UNKNOWN rather than YES or NO.

Namespace-scoped privilege is also UNKNOWN. The patch does not establish that all required operations can be performed inside attacker-created namespaces.

Prior host setup may be required if the attacker cannot configure the SLIP line discipline or obtain access to a suitable tty. No special hardware requirement is established beyond a tty/SLIP configuration. The race is real, but not penalized as a hard race because repeatability and attacker control over both sides are not fully resolved.

4. Primitive and severity interpretation

The exact primitive is a real kernel use-after-free read of SLIP private state. The object is an active structured object, not fixed stale DMA or USB storage. The stale use occurs in slip_receive_buf() or related reader paths while slip_close() has freed the underlying netdev/private state.

This is not an ordinary stale cleanup dereference. It is an active receive-path lifetime violation. However, it is also not CLASS_A because the patch does not establish controlled reclaim, attacker-shaped replacement contents, arbitrary kernel read/write, callback control, or demonstrated privilege escalation.

PrimitiveClass is CLASS_B. The demonstrated consequence is kernel crash or DoS. The speculative consequence is possible C/I impact or privilege escalation if an attacker can obtain useful post-free reuse, but that is not established by the supplied evidence. ImportantCandidate is YES because a real active-object UAF in a receive path has unresolved exploitation leverage. AutoDowngradeAllowed is NO because automatic closure would discard a concrete kernel lifetime-corruption primitive that still needs manual Important-vs-Moderate review.

Likely operational severity is Actionable Moderate at minimum, with manual review needed before ruling out Important-class impact.

5. One-sentence report phrase

A race between SLIP tty hangup and slip_receive_buf() can free the SLIP net device and private state while receive processing still dereferences it, causing a real local kernel use-after-free with at least DoS impact and unresolved exploitation potential.

6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is a concrete kernel UAF in an active receive path, not a pure warning, resource leak, or crash-only validation bug. Controlled exploitation is not proven, but automatic downgrade would be unsafe.

7. Call-site confidence

Call-site confidence: high

======================================================================
UPSTREAM PATCH SUMMARY
======================================================================

Patch: slip: remove slip_hangup() to fix use-after-free in slip_receive_buf() [ Upstream
Commit: 9a3b1edff1ecb47d323f2506b3ffc22178acd1c6
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9a3b1edff1ecb47d323f2506b3ffc22178acd1c6

Changed files:
  drivers/net/slip/slip.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=9a3b1edff1ecb47d323f2506b3ffc22178acd1c6

======================================================================
DETAILED REPORT METHODOLOGY
======================================================================

The original Linux kernel CVE announcement for CVE-2026-90057 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90057

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:H/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 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: 4
  Paranoid ActionableScore: 5

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: YES
Published priority for this report (same as in Subject): MODERATE 7.0

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 alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).