[CVE-2026-72029][MODERATE 7.0] net: wwan: iosm: bound device offsets in the MUX downlink decoder

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

CVE: CVE-2026-72029
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: net: wwan: iosm: bound device offsets in the MUX downlink decoder
Commit: 155851e501d6c649cbcfcca6472dc26269b04b6b
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=155851e501d6c649cbcfcca6472dc26269b04b6b
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72029
Analysis date: Sat, 15 Aug 2026 03:53:29 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A device supplied MUX downlink table in the iosm WWAN driver can contain unchecked offsets and cyclic next table indexes, allowing a malicious or compromised modem path to trigger slab out of bounds reads or a softirq infinite loop causing kernel DoS.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-72029 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72029

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-2026-72029	MODERATE	CHECK WITH IMPACT FROM ORIG NN LOW	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-20;*CWE-835;**CWE-400;Other CVSS 'AV:A/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H';BEST CVSS score: '7.6';DESCR 'The iosm WWAN MUX downlink decoder trusted modem supplied offsets and lengths when walking aggregated datagram tables. A malicious or compromised WWAN modem, or an adjacent cellular side able to influence modem downlink MUX frames, can provide table indexes or datagram lengths outside the received skb and trigger a slab out of bounds read. The same parser also followed next table indexes without a forward progress check, so crafted tables can form a cycle and keep the softirq path running while repeatedly cloning skbs. For the CVSS the PR:N is used because the malformed data is supplied by the device side and no local account on the host is required when the attacker controls that input path. The issue is not a normal Internet remote bug and is better modeled as AV:A because practical exploitation requires access to the WWAN modem or adjacent cellular data path. Impact is at least denial of service through kernel crash or softirq lockup, with limited confidentiality or integrity impact considered in the paranoid score due to the out of bounds read primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	READ KASAN OOB NETWORK SKB HARDWARE LINUS PACKET  INCREASED_TO_MODERATE7_BASED_ON_GUESSCVSS DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP	YES	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

Triggered signals:

* Firmware-mediated external influence: +1
  The malformed offsets and lengths are supplied by the WWAN modem or modem-controlled downlink path, not by an ordinary local syscall path.

* Memory corruption, weak/indirect corruption candidate: +1
  The decoder forms in-kernel pointers from unchecked device-supplied indexes and interprets out-of-bounds memory as MUX table structures. This is supported by the KASAN slab out-of-bounds read, but there is no OOB write or controlled overwrite.

* Reliable kernel crash / strong DoS: +1
  The bug was reproduced as a KASAN slab OOB read on normal downlink receive after the iosm netdev is up. The table-chain cycle can also cause an infinite softirq loop with repeated skb cloning.

* Availability impact realistic: +1
  The infinite loop in softirq and repeated skb cloning can create system-impacting DoS beyond a single benign warning.

* Privileged kernel/device-management memory corruption path: +1
  The parser consumes firmware/device-supplied structures in a trusted kernel WWAN driver receive path.

* Rare AND difficult-to-reach subsystem/configuration: -1
  The issue requires the iosm WWAN device/driver and a reachable modem downlink MUX path, so exposure is narrower than core networking.

Paranoid-only signal:

* Confidentiality impact plausible: +1
  The demonstrated primitive is an OOB read from slab memory. There is no clear disclosure channel in the patch, but limited confidentiality concern is defensible for manual-review sensitivity.

Not awarded:

* Remote reachable / network-triggerable: +0
  This is not a normal Internet-reachable network parser. AV is better viewed as firmware-mediated or adjacent cellular/modem influenced.

* Strong LPE plausibility: +0
  No UAF, OOB write, arbitrary write, callback control, refcount takeover, or attacker-controlled reclaim is shown.

* Integrity impact: +0 conservative
  No write primitive or ownership/COW bypass is demonstrated.

## 3. Reachability analysis

The most realistic trigger is a malicious, compromised, or misbehaving WWAN modem supplying malformed MUX downlink tables. A more external scenario may exist if an adjacent cellular-side attacker can influence the modem downlink MUX frames, but this is not equivalent to an ordinary AV:N Internet attack.

Local namespaces and containers do not materially lower the privilege requirement because the malformed data is device-originated. A local unprivileged user normally cannot directly craft these MUX frames unless they already control the modem path or a privileged management component.

The path is not broadly default-exposed across Linux systems. It applies to systems using the Intel iosm WWAN driver with the relevant net device up.

Call-site confidence: high. The patch includes the vulnerable parsing function and the downstream datagram processing bounds checks.

## 4. Severity interpretation

This behaves more like an actionable Moderate than an ordinary Moderate. The realistic impact is DoS through kernel crash or softirq lockup. The demonstrated memory issue is OOB read, not OOB write, so Important-class LPE is not strongly supported.

The paranoid score reaches Actionable Moderate because the input is firmware/device controlled, the parser trusted multiple unbounded offsets, KASAN reproduced slab OOB read, and the loop can be forced not to progress. It should not be auto-closed without manual review.

## 5. One-sentence report phrase

A device supplied MUX downlink table in the iosm WWAN driver can contain unchecked offsets and cyclic next table indexes, allowing a malicious or compromised modem path to trigger slab out of bounds reads or a softirq infinite loop causing kernel DoS.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: device-supplied parser input plus KASAN-confirmed slab OOB read and a softirq infinite-loop condition make this more than a simple validation cleanup, even though the current evidence supports DoS and limited OOB-read concern rather than proven privilege escalation.

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

Patch: net: wwan: iosm: bound device offsets in the MUX downlink decoder
Commit: 155851e501d6c649cbcfcca6472dc26269b04b6b
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=155851e501d6c649cbcfcca6472dc26269b04b6b

Commit description:

mux_dl_adb_decode() walks a chain of aggregated datagram tables using
offsets and lengths taken from the modem. first_table_index,
next_table_index, table_length, datagram_index and datagram_length are
all device supplied le values. Only first_table_index was checked, and
only for being non zero. The decoder then formed adth = block +
adth_index and read the table header and the datagram entries with no
bound against the received skb. A modem that reports an index or a
length past the downlink buffer makes the decoder read out of bounds.

The buffer is IPC_MEM_MAX_DL_MUX_LITE_BUF_SIZE and skb->len is at most
that, so skb->len is the real limit, but none of these in band offsets
were checked against it.

The table chain is also followed with no forward progress check. The loop
takes the next table from adth->next_table_index and stops only when that
reaches zero. A modem can stage two tables that point at each other, so
the loop never ends. It runs in softirq and clones the skb on every pass.

Validate every device offset and length against skb->len before use.
The block header must fit. Each table header, on entry and after every
next_table_index, must lie inside the skb. The datagram table must fit.
Each datagram index and length must stay inside the skb. The header
padding must not exceed the datagram length so the receive length does
not wrap. Require each next_table_index to move forward so the chain
cannot cycle.

This was reproduced under KASAN as a slab out of bounds read on a normal
downlink receive once the iosm net device is up.

Fixes: 1f52d7b ("net: wwan: iosm: Enable M.2 7360 WWAN card support")
Suggested-by: Loic Poulain <loic.poulain@oss.qualcomm.com>
Cc: stable@vger.kernel.org
Signed-off-by: Maoyi Xie <maoyixie.tju@gmail.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Reviewed-by: Loic Poulain <loic.poulain@oss.qualcomm.com>
Link: https://patch.msgid.link/178236824878.3259367.5389624724479864947@maoyixie.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/net/wwan/iosm/iosm_ipc_mux_codec.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=155851e501d6c649cbcfcca6472dc26269b04b6b

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

The original Linux kernel CVE announcement for CVE-2026-72029 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72029

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:L/PR:N/UI:N/S:U/C:L/I:N/A:H
  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: 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: NO
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).