[CVE-2026-53088][MODERATE REGULAR] net: bcmgenet: fix off-by-one in bcmgenet_put_txcb [ Upstream

[CVE-2026-53088][MODERATE REGULAR] net: bcmgenet: fix off-by-one in bcmgenet_put_txcb [ Upstream

[AL-KERNEL]

CVE: CVE-2026-53088
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: net: bcmgenet: fix off-by-one in bcmgenet_put_txcb [ Upstream
Commit: 14e9f86564fff7bcf7f45c1b69080e837b31d185
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=14e9f86564fff7bcf7f45c1b69080e837b31d185
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53088
Analysis date: Tue, 30 Jun 2026 21:33:58 -0400
ActionableScore: 4
ActionableScore lower bound: 3
Actionable bucket: Borderline, manual review recommended
Manual review required: YES

Summary:
An off-by-one bug in bcmgenet_put_txcb can return the wrong TX control block during error unwind, causing incorrect DMA/TX cleanup and possible local DoS or driver state corruption on affected Broadcom GENET systems.

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

The original Linux kernel CVE announcement for CVE-2026-53088 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53088

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.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-53088	MODERATE	CHECK	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';CWE-193;CWE-404;*CWE-772;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.8';DESCR 'An off by one error in bcmgenet_put_txcb() can make the TX error unwind path return the next free tx_cb instead of the tx_cb that was actually rewound. This can cause cleanup to target the wrong TX control block while the real descriptor state or DMA mapping may remain uncleared. For the CVSS the PR:L is used because a local unprivileged user may be able to generate outgoing traffic that reaches the driver TX path, while reliable triggering still depends on an error unwind condition in the hardware or DMA mapping path. The issue is not directly network reachable in the normal remote packet processing sense. Impact is at least local denial of service through TX resource leakage or device malfunction. In the paranoid interpretation, limited confidentiality or integrity impact is kept possible because the bug affects DMA descriptor cleanup, but the patch does not show a strong arbitrary write primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline, manual review recommended (with actual score 4)	YES	REMOTE SIMPLEFIX NETWORK LINUS  LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	guess

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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

Conservative signals:

* Local unprivileged trigger: +1. A local user can plausibly generate outbound traffic through the bcmgenet TX path, although reaching the exact unwind path likely requires an error condition.
* Memory corruption, weak/indirect corruption candidate: +1. The helper can return the wrong TX control block, causing cleanup to apply to the wrong descriptor/control object.
* Privileged kernel/device-management memory corruption path: +1. The affected code is DMA-adjacent TX ring/control-block cleanup in a NIC driver.
* Availability impact realistic: +1. Incorrect TX cleanup can plausibly cause DMA mapping leaks, TX ring inconsistency, device malfunction, or local DoS.
* Hard or unreliable trigger: -1. The vulnerable behavior appears to require the TX error/unwind path rather than normal successful packet transmission.

Paranoid additional signal:

* Real lifetime corruption concern: +1. Wrong-object cleanup in a TX rollback helper may leave the actually used tx_cb or DMA mapping stale, with possible later double cleanup, stale descriptor state, or queue corruption.

Not counted:

* No remote reachable score. This is a transmit-side local driver path, not normal remote packet receive parsing.
* No strong memory corruption score. The patch does not show attacker-controlled overwrite, UAF reclaim, arbitrary write, callback control, or type confusion.
* No privilege escalation score. LPE is not supported by the patch context beyond a weak theoretical DMA/lifetime concern.

## 3. Reachability analysis

The most plausible trigger is a local user or process that can send traffic through a Broadcom GENET interface while an error path in bcmgenet_xmit or fragment unmapping is reached. No CAP_NET_ADMIN is clearly required just to transmit packets, so PR:L is the practical assumption, but reliable triggering depends on driver, DMA, skb fragment, or hardware error conditions. Containers or namespaces may lower practical reachability if they can transmit through the affected device, but the bug is still hardware and driver specific. The path is not Internet remote in the usual sense because incoming packets do not directly exercise this TX rollback helper.

Call-site confidence: medium. The patch shows the helper and the commit explains cleanup semantics, but the full caller context is not included.

## 4. Severity interpretation

This behaves more like a borderline actionable Moderate than an Important issue. The theoretical concern is wrong-object cleanup in a DMA TX ring, which can hide lifetime or descriptor corruption effects. The realistic evidence is weaker: the patch only fixes an off-by-one pointer-return bug in an unwind helper, with no KASAN report, no demonstrated UAF, no arbitrary write, and no clear privilege-escalation primitive. Manual review is justified because DMA cleanup bugs can be under-described, but the issue should not be treated as Strong Important from the provided evidence alone.

## 5. One-sentence report phrase

An off-by-one bug in bcmgenet_put_txcb can return the wrong TX control block during error unwind, causing incorrect DMA/TX cleanup and possible local DoS or driver state corruption on affected Broadcom GENET systems.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: wrong-object cleanup in a DMA-adjacent TX rollback helper is security-relevant enough for review, but the patch does not show a strong memory corruption primitive, remote reachability, or demonstrated privilege escalation.

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

Patch: net: bcmgenet: fix off-by-one in bcmgenet_put_txcb [ Upstream
Commit: 14e9f86564fff7bcf7f45c1b69080e837b31d185
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=14e9f86564fff7bcf7f45c1b69080e837b31d185

Changed files:
  drivers/net/ethernet/broadcom/genet/bcmgenet.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=14e9f86564fff7bcf7f45c1b69080e837b31d185

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

The original Linux kernel CVE announcement for CVE-2026-53088 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53088

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:L/I:L/A:H
  The Best / paranoid CVSS score: 5.8

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).