[CVE-2026-74270][IMPORTANT] handshake: Require admin permission for DONE command [ Upstream

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

CVE: CVE-2026-74270
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: NO
Patch: handshake: Require admin permission for DONE command [ Upstream
Commit: 25fb53e43ec006ac69b9e825a7e8a11d63a6083e
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=25fb53e43ec006ac69b9e825a7e8a11d63a6083e
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74270
Analysis date: Sat, 15 Aug 2026 05:50:37 -0400
ActionableScore: 7
ActionableScore lower bound: 5
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A missing GENL_ADMIN_PERM check on the handshake Generic Netlink DONE command allows a local unprivileged process with access to a valid pending handshake sockfd to forge handshake success or failure, potentially bypassing trusted-agent authentication state or causing handshake denial of service.

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

The original Linux kernel CVE announcement for CVE-2026-74270 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74270

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: IMPORTANT
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-2026-74270	IMPORTANT	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-862;CWE-306;CWE-287;CWE-284;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:L';BEST CVSS score: '7';DESCR 'handshake Generic Netlink DONE lacked the GENL_ADMIN_PERM check even though DONE is intended for the trusted handshake agent. A local unprivileged process that can guess observe or otherwise obtain a valid pending sockfd may send a forged DONE status and make the kernel consumer treat an unfinished handshake as successful, or send a failure status to abort a legitimate in flight handshake. For the CVSS the PR:L is used because triggering requires local code able to issue the Generic Netlink command but does not require administrator privileges before the fix. The issue is not directly network reachable because packets alone do not invoke the vulnerable DONE command. Impact is at least denial of service and an integrity bypass of the kernel handshake control path. For the paranoid score, choose the highest still-defensible interpretation because a forged successful handshake may affect authentication state and secure transport assumptions.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7)	YES	SIMPLEFIX IMPROVEONLY 	YES	NO	checked

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

ActionableScore=7
ActionableScoreLower=5

## 1. ActionableScore

* Conservative score: 5
* Paranoid score: 7
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: +1. The DONE Generic Netlink command was callable without GENL_ADMIN_PERM.
* Security-boundary bypass with practical sensitive-object access: +2. DONE is intended for the trusted handshake agent, but an unprivileged sender could report completion to the kernel consumer.
* Practical exploit chain strongly implied: +1. Forged DONE with status 0 can make the consumer proceed as if the handshake succeeded, while non-zero status can abort a legitimate in-flight handshake.
* Integrity impact plausible: +1. The attacker can influence handshake result state and bypass the intended trusted-agent decision point.
* Availability impact realistic: +1. Forged failure can tear down legitimate pending handshakes.
* Hard or unreliable timing / object condition: -1. Triggering requires a pending handshake and a valid sockfd that can be guessed, observed, inherited, or otherwise available.

Paranoid additional signals:

* Confidentiality impact plausible: +1. If the affected kernel consumer relies on the handshake result for protected transport state, forged success can undermine confidentiality assumptions.
* Cross-boundary policy bypass: +1. The bug bypasses the intended privilege boundary between ordinary local processes and the trusted tlshd handshake agent.

No memory-corruption signals are awarded. This is an authorization / authentication bypass, not UAF, OOB, double-free, or type confusion.

## 3. Reachability analysis

The trigger is local via Generic Netlink, not directly remote packet traffic. A local unprivileged process can issue the vulnerable DONE operation before the fix, but practical triggering depends on a valid in-flight handshake request and a relevant sockfd. Namespaces and service models matter because reduced-capability root, container contexts, or service accounts may still be meaningful attackers if they can reach the netlink family and relevant socket state. The affected path is only relevant on systems using the kernel handshake infrastructure and a trusted userspace agent such as tlshd.

Call-site confidence: medium. The patch and commit message clearly show the missing permission check and the intended trusted-agent boundary, but product impact depends on which kernel consumers use this handshake path.

## 4. Severity interpretation

This behaves more like an actionable Moderate or Strong Important candidate than an ordinary Moderate. There is no demonstrated memory corruption or direct LPE primitive, but the flaw bypasses a security control in a handshake completion path. Realistic impact is integrity bypass and handshake disruption. Paranoid impact is higher because forged successful completion can affect authentication and secure transport assumptions.

## 5. One-sentence report phrase

A missing GENL_ADMIN_PERM check on the handshake Generic Netlink DONE command allows a local unprivileged process with access to a valid pending handshake sockfd to forge handshake success or failure, potentially bypassing trusted-agent authentication state or causing handshake denial of service.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED. YES REQUIRES MANUAL CHECK.

This should not be auto-closed because it is a missing authorization check in a security handshake control path, with plausible integrity impact and deployment-dependent confidentiality consequences.

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

Patch: handshake: Require admin permission for DONE command [ Upstream
Commit: 25fb53e43ec006ac69b9e825a7e8a11d63a6083e
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=25fb53e43ec006ac69b9e825a7e8a11d63a6083e

Changed files:
  net/handshake/genl.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=25fb53e43ec006ac69b9e825a7e8a11d63a6083e

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

The original Linux kernel CVE announcement for CVE-2026-74270 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74270

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:H/A:L
  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: 5
  Paranoid ActionableScore: 7

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: IMPORTANT
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): IMPORTANT

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).