[CVE-2026-74282][MODERATE REGULAR] tipc: prevent snt_unacked underflow on CONN_ACK [ Upstream

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

CVE: CVE-2026-74282
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: tipc: prevent snt_unacked underflow on CONN_ACK [ Upstream
Commit: 3388145d258cf2c4c98278e3987296007d30672e
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3388145d258cf2c4c98278e3987296007d30672e
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74282
Analysis date: Sun, 16 Aug 2026 05:56:43 -0400
ActionableScore: 4
ActionableScore lower bound: 3
Actionable bucket: Borderline / manual review recommended
Manual review required: YES

Summary:
A peer supplied TIPC CONN_ACK with an oversized ACK count can underflow the snt_unacked counter, permanently mark the connection as congested, and cause a denial of service for the affected TIPC connection or dependent service.

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

The original Linux kernel CVE announcement for CVE-2026-74282 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74282

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-2026-74282	MODERATE	CHECK WITH IMPACT FROM ORIG NN IMPORTANT	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L';CWE-191;*CWE-20;**CWE-400;Other CVSS 'AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.3';DESCR 'A peer supplied TIPC CONN_ACK can acknowledge more messages than are actually outstanding, causing the unsigned 16 bit snt_unacked counter to underflow. This can leave the connection permanently marked as congested and starve the send side of further transmits, resulting in a denial of service for that TIPC connection or a dependent service. For the CVSS the PR:N applies because a connected peer can send the malformed CONN_ACK without a local account on the target. The issue is network reachable only where the attacker can reach the relevant TIPC bearer or peer relationship. TIPC is typically used in clustered or internal systems rather than exposed directly to the public Internet. Impact is denial of service only based on the visible protocol counter underflow, with no concrete memory corruption or privilege escalation primitive shown by the patch.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 4)	YES	OOB INIT SIMPLEFIX TIPC LINUS  LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	checked

======================================================================
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: +2
  * A malformed CONN_ACK is peer supplied and processed from received TIPC connection protocol messages. This is network or cluster peer reachable when the relevant TIPC bearer is exposed.
* Availability impact realistic: +1
  * The oversized ACK can underflow snt_unacked and leave tsk_conn_cong() permanently true, starving the connection send side.
* Reliable DoS / strong service-level DoS: +1 in paranoid scoring only
  * The impact is not a kernel crash, but the commit describes a durable connection wedge. This is a strong per-connection or dependent-service DoS when the attacker can act as a peer.
* Rare or configuration-dependent subsystem: -1 in conservative scoring
  * TIPC is commonly used in clustered or internal systems and is not usually exposed to the public Internet.

No memory corruption, UAF, OOB write, arbitrary write, info leak, or privilege escalation primitive is supported by the patch.

## 3. Reachability analysis

The bug can be triggered by a connected TIPC peer, or by the connected local peer socket for local connections, by sending a CONN_ACK with an ACK count larger than the number of outstanding messages. No local account on the victim is required if the attacker can reach and participate in the relevant TIPC communication path. In typical deployments TIPC is not Internet exposed and is more likely limited to cluster, storage, telecom, or internal node networks. Namespaces may affect local access to TIPC sockets, but the main concern here is peer reachability rather than local privilege.

## 4. Severity interpretation

This behaves like an actionable network-adjacent Moderate issue, not an Important-class kernel memory corruption bug. The integer underflow corrupts protocol accounting state and can wedge a connection, but the patch does not show attacker-controlled memory corruption, stale object reuse, type confusion, or a privilege escalation path. The practical risk is denial of service for a TIPC connection or service dependency, with higher priority if TIPC is reachable by untrusted peers.

## 5. One-sentence report phrase

A peer supplied TIPC CONN_ACK with an oversized ACK count can underflow the snt_unacked counter, permanently mark the connection as congested, and cause a denial of service for the affected TIPC connection or dependent service.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

This should not be treated as Important by default, but manual review is recommended because it is peer reachable over a networking protocol and can cause a durable availability failure when TIPC is exposed to untrusted or semi-trusted nodes.

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

Patch: tipc: prevent snt_unacked underflow on CONN_ACK [ Upstream
Commit: 3388145d258cf2c4c98278e3987296007d30672e
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3388145d258cf2c4c98278e3987296007d30672e

Changed files:
  net/tipc/socket.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=3388145d258cf2c4c98278e3987296007d30672e

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

The original Linux kernel CVE announcement for CVE-2026-74282 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74282

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:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS score: 5.3

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).