[CVE-2026-45843][MODERATE REGULAR] slip: bound decode() reads against the compressed packet length [ Upstream

[CVE-2026-45843][MODERATE REGULAR] slip: bound decode() reads against the compressed packet length [ Upstream

[AL-KERNEL]

CVE: CVE-2026-45843
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: slip: bound decode() reads against the compressed packet length [ Upstream
Commit: 37537e42e6df387398bee85cb85070cc80bb1e10
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=37537e42e6df387398bee85cb85070cc80bb1e10
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45843
Analysis date: Wed, 27 May 2026 06:05:41 -0400
ActionableScore: 4
ActionableScore lower bound: 3
Actionable bucket: Borderline, manual review recommended
Manual review required: YES

Summary:
A short VJ-compressed SLIP frame can make `slhc_uncompress()` read past the compressed packet and fold over-read bytes into cached TCP/IP state, causing limited information exposure or reconstructed-packet corruption on affected SLIP links.

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

The original Linux kernel CVE announcement for CVE-2026-45843 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45843

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: YES

A detailed explanation of the methodology and priority rules is included
at the end of this message.

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-45843	MODERATE	CHECK	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H';CWE-125;*CWE-200;*CWE-20;Other CVSS 'AV:A/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:L';BEST CVSS score: '7.6';DESCR 'SLIP VJ header decompression in slhc_uncompress can read beyond the compressed frame because decode and pull16 advanced through optional fields without checking the packet end. A short compressed frame can make overread bytes influence cached cstate and later reconstructed TCP/IP packets, so an adjacent SLIP peer may cause limited information exposure or packet/header corruption. For the CVSS the PR:N is used for the paranoid score because a peer on an already configured SLIP/VJ link can send crafted compressed frames without privileges on the victim. The issue is not Internet remote and depends on SLIP with VJ compression, which is uncommon. Impact is mainly limited confidentiality and integrity impact plus possible connection disruption, with no evidence of kernel memory write or privilege escalation.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline, manual review recommended (with actual score 4)	YES	OOB ERRORPATH NETWORK TEST PACKET  INCREASED_TO_MODERATE7_BASED_ON_GUESSCVSS DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	checked

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

ActionableScore=4
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 4
* Final recommended bucket: **Borderline, manual review recommended**::

## 2. Signal breakdown

* Remote reachable / network-triggerable adjacent path: +2. A peer on an already configured SLIP link with VJ compression can send a short crafted compressed frame that reaches `slhc_uncompress()`.
* Confidentiality impact plausible: +1. The over-read bytes can be folded into cached `cstate` and reflected into later reconstructed packets, giving a limited possible disclosure path.
* Integrity impact plausible: +1. Corrupted cached TCP/IP header state can affect later reconstructed packets.
* Availability impact plausible: +1 paranoid only. Malformed compressed frames can disrupt the SLIP/VJ connection state, but the patch does not show a kernel crash or system-wide DoS.
* Rare and configuration-dependent subsystem: -1. SLIP with Van Jacobson compression is uncommon and requires an already configured link.
* No strong memory corruption signal. This is an OOB read from packet-adjacent memory, not UAF, OOB write, heap overwrite, arbitrary write, or refcount corruption.
* No LPE signal. The patch does not support privilege escalation.

Conservative total: 3.
Paranoid total: 4.

## 3. Reachability analysis

The trigger is a malformed VJ-compressed frame received over a SLIP link. The sender does not need privileges on the victim once the SLIP/VJ link is configured, so the attacker model is an adjacent link peer rather than a local user.

This is not Internet remote in the normal sense. It depends on SLIP and VJ header compression being active, which is rare in modern deployments. Namespaces and containers are not the main factor here because the trigger comes from the link peer, while configuring SLIP typically requires administrative setup.

Realistic exploitation is limited by deployment rarity, but if the configuration exists, the malformed frame path is direct and does not require a timing race.

## 4. Severity interpretation

This behaves like a borderline Moderate networking parser issue. It is more serious than a pure malformed-packet drop because the over-read data can be incorporated into cached decompression state and reflected into later packets. However, it is not an Important-class kernel memory corruption issue because there is no write primitive, no UAF, no demonstrated kernel crash, and no plausible privilege-escalation path from the patch.

Theoretical impact is limited information exposure or packet/header corruption. Realistic impact is likely connection disruption or incorrect reconstructed packets on rare SLIP/VJ deployments.

## 5. One-sentence report phrase

A short VJ-compressed SLIP frame can make `slhc_uncompress()` read past the compressed packet and fold over-read bytes into cached TCP/IP state, causing limited information exposure or reconstructed-packet corruption on affected SLIP links.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED.

Reason: this is an adjacent packet-parser OOB read with possible reflected state corruption, but exposure is rare and there is no evidence of kernel memory write, UAF, privilege escalation, or system-wide crash.

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

Patch: slip: bound decode() reads against the compressed packet length [ Upstream
Commit: 37537e42e6df387398bee85cb85070cc80bb1e10
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=37537e42e6df387398bee85cb85070cc80bb1e10

Changed files:
  drivers/net/slip/slhc.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=37537e42e6df387398bee85cb85070cc80bb1e10

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

The original Linux kernel CVE announcement for CVE-2026-45843 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45843

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:A/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:L
  The Best / paranoid CVSS vector: AV:A/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 7.6

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: 3
  Paranoid ActionableScore: 4

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