[CVE-2026-68143][MODERATE 7.0] net: slip: serialize receive against buffer reallocation

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

CVE: CVE-2026-68143
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: net: slip: serialize receive against buffer reallocation
Commit: eb3836eab47487823f362e6985e170a1e15f20fd
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=eb3836eab47487823f362e6985e170a1e15f20fd
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68143
Analysis date: Mon, 10 Aug 2026 13:43:25 -0400
ActionableScore: 6
ActionableScore lower bound: 4
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A race in the SLIP receive path can allow MTU-driven buffer reallocation to overlap with writes through rbuff, causing an out-of-bounds write or use-after-free write and making this a local kernel memory corruption issue requiring manual review.

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

The original Linux kernel CVE announcement for CVE-2026-68143 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68143

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.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-68143	MODERATE	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-362;*CWE-787;*CWE-416;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A race in the SLIP driver can occur because sl_realloc_bufs() replaces rbuff and updates buffsize under sl lock, while slip_receive_buf() previously consumed received bytes and wrote through rbuff without holding the same lock. An MTU shrink can expose a smaller receive buffer while the receive path still uses an older larger bound, causing an out-of-bounds write. A receive callback can also keep using an old rbuff after it was freed by reallocation, causing a use-after-free write. For the CVSS the PR:L is used because reliable triggering can be possible for a local user or delegated network administrator that can operate the SLIP device or change MTU, without requiring full host root in reduced capability setups. The issue is not directly Internet reachable, but a peer on a SLIP link may help supply receive traffic while the local control path changes MTU. Impact is at least a local denial of service via kernel crash and in the worst case may allow confidentiality and integrity impact due to kernel memory corruption.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 5)	YES	WRITE OOB LOCK SIMPLEFIX RACE NETWORK LINUS KPANIC  KPANIC DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN7	NO	NO	checked

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

ActionableScore=6
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 6
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Triggered signals:

* Memory corruption, strong corruption primitive: +2
  The commit explicitly describes an out-of-bounds write when an MTU shrink exposes a smaller rbuff while receive processing still uses the old larger bound.

* Real lifetime corruption: +1
  The commit explicitly describes a stale rbuff use after sl_realloc_bufs() frees the old receive buffer, producing a use-after-free write.

* Reliable kernel crash / strong DoS: +1
  OOB write and UAF write in a network driver receive path are realistic kernel crash primitives.

* Weak LPE concern conservative: +1
  The bug gives kernel memory corruption, but the patch does not demonstrate controlled reclaim, reliable object replacement, callback control, or arbitrary write.

* Stronger LPE plausibility paranoid: +2
  For the paranoid score, the primitive is not just a NULL dereference. It is a write-after-free or OOB write with attacker-influenced receive bytes, so privilege escalation deserves manual-review sensitivity.

* Local trigger through privileged or delegated network control: +1 paranoid only
  A local actor able to operate the SLIP device and change MTU can race receive processing. In container or delegated CAP_NET_ADMIN setups this may be less than full host-root.

Negative signals:

* Hard or unreliable race / special timing required: -1
  The bug depends on racing receive processing with MTU-triggered buffer reallocation.

* Requires CAP_NET_ADMIN or equivalent in typical deployments: -2 conservative, -1 paranoid
  In ordinary systems, reliable triggering likely needs network-device control. The paranoid score reduces the penalty because CAP_NET_ADMIN may be delegated to containers, network namespaces, or service accounts.

* Rare / non-default subsystem exposure: -1
  SLIP is legacy and not broadly enabled in modern default deployments.

## 3. Reachability analysis

The issue is locally triggerable by an actor that can configure or operate a SLIP network device and race receive input against MTU changes. In typical deployments this requires CAP_NET_ADMIN or equivalent control over the SLIP interface and its TTY backing device. It is not directly Internet reachable.

Namespaces and containers matter because CAP_NET_ADMIN may be delegated without granting full host-root privileges. If an untrusted container or service account can create or control a SLIP interface, the practical PR interpretation becomes closer to PR:L than PR:H. A remote peer on the SLIP link may help provide the receive traffic, but the core trigger still depends on local control of the MTU or device configuration.

The affected path is not a common default networking path. SLIP is legacy and uncommon, which lowers broad exposure. However, when present, the primitive is real kernel memory corruption rather than a pure warning or resource leak.

## 4. Severity interpretation

This is stronger than an ordinary Moderate DoS because the patch and commit message explicitly identify both OOB write and UAF write conditions. Conservative handling is Borderline / manual review recommended due to the hard race, CAP_NET_ADMIN requirement, and rare subsystem exposure.

The paranoid interpretation reaches Actionable Moderate / Important candidate territory because kernel write-after-free and out-of-bounds write bugs have historically been under-triaged when the initial report only shows a crash. Realistic exploitation evidence is not demonstrated in the patch, but the memory corruption class is concrete enough to avoid auto-closure.

## 5. One-sentence report phrase

A race in the SLIP receive path can allow MTU-driven buffer reallocation to overlap with writes through rbuff, causing an out-of-bounds write or use-after-free write and making this a local kernel memory corruption issue requiring manual review.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: the patch explicitly describes OOB write and UAF write primitives in kernel memory. Even though triggering likely requires CAP_NET_ADMIN or delegated network control and SLIP is uncommon, this should not be auto-closed because privilege escalation is technically plausible and the final impact depends on allocator behavior, object reuse, and attacker control of receive data.

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

Patch: net: slip: serialize receive against buffer reallocation
Commit: eb3836eab47487823f362e6985e170a1e15f20fd
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=eb3836eab47487823f362e6985e170a1e15f20fd

Commit description:

sl_realloc_bufs() replaces rbuff and updates buffsize while holding
sl->lock. slip_receive_buf() reads those fields and writes through rbuff
without holding the lock.

An MTU change can therefore race with receive processing. An MTU shrink
can expose the new smaller rbuff with the old larger bound, causing an
out-of-bounds write. A receive callback which already loaded the old
rbuff can instead continue writing after that buffer has been freed.

Serialize receive processing with sl_realloc_bufs() by holding sl->lock
while consuming each receive batch.

Fixes: 1da177e ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Signed-off-by: Sungmin Kang <726ksm@gmail.com>
Link: https://patch.msgid.link/20260718073631.1674-1-726ksm@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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=eb3836eab47487823f362e6985e170a1e15f20fd

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

The original Linux kernel CVE announcement for CVE-2026-68143 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68143

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:L/I:L/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: 6

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).