[CVE-2026-46193][MODERATE 7.0] xfrm: ah: account for ESN high bits in async callbacks [ Upstream

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

CVE: CVE-2026-46193
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: xfrm: ah: account for ESN high bits in async callbacks [ Upstream
Commit: 0555d4f526232b3c9e3afbcd490c0c0793aefec6
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0555d4f526232b3c9e3afbcd490c0c0793aefec6
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46193
Analysis date: Thu, 28 May 2026 10:00:35 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: NO

Summary:
XFRM AH async callbacks failed to account for the ESN high bits slot, causing wrong ICV or auth_data offsets and allowing valid AH ESN traffic to be dropped in affected async crypto configurations.

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

The original Linux kernel CVE announcement for CVE-2026-46193 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46193

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: NO

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-2026-46193	MODERATE	CHECK	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';CWE-682;CWE-354;CWE-345;CWE-693;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.9';DESCR 'XFRM AH async completion callbacks did not account for the ESN high bits slot when reconstructing the temporary authentication layout. With AH plus ESN and an async ahash implementation, the callbacks can copy or compare bytes at the wrong offset, causing valid AH packets to fail authentication and resulting in packet loss. For the CVSS the PR:N is used because the affected behavior is in the network packet path once AH ESN and async crypto are configured, and a peer can send traffic over that path without local privileges on the victim. The issue is network reachable only for systems using this specific IPsec AH ESN async configuration. Impact is availability only through AH traffic failure, with no supported memory corruption, information disclosure, authentication bypass, or privilege escalation primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5) 	MAYBE	REMOTE DANGER NETWORK HARDWARE LINUS TEST IPV6 KPANIC PACKET 	-	-	checked

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

ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

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

## 2. Signal breakdown

Conservative signals:

* Remote reachable / network-triggerable: +2. The affected behavior is in the XFRM AH packet path once AH, ESN, and async crypto are configured.
* Reliable service DoS: +1. Valid AH packets can fail authentication because callbacks use the wrong auth or ICV offsets.
* Availability impact realistic: +1. The observed impact is 100 percent packet loss for the affected AH ESN async configuration.

Paranoid additional signal:

* Networking / XFRM packet-processing path: +1. XFRM/IPsec traffic protection is security-sensitive infrastructure, so packet-path availability failures deserve manual triage even when configuration-specific.

Not counted:

* No memory corruption.
* No UAF, OOB write, arbitrary write, or information leak.
* No authentication bypass is supported. The bug causes valid packets to be rejected, not invalid packets to be accepted.
* No privilege escalation primitive.

## 3. Reachability analysis

A network peer can trigger the affected path by sending traffic over an already configured AH SA using ESN and an async ahash implementation. The attacker does not need local privileges on the victim, but the system must use this specific IPsec AH ESN async configuration.

This is not a generic Internet-facing parser bug on all systems. It is configuration-dependent and mainly affects deployments using AH with ESN and async software or hardware crypto. No namespace or container privilege change is central to the trigger.

## 4. Severity interpretation

This behaves like an actionable Moderate availability issue. The realistic evidence is packet authentication failure and traffic loss.

It does not behave like an Important memory-corruption issue. The patch only corrects temporary buffer layout offsets in async callbacks, and there is no supported confidentiality, integrity, or LPE impact.

## 5. One-sentence report phrase

XFRM AH async callbacks failed to account for the ESN high bits slot, causing wrong ICV or auth_data offsets and allowing valid AH ESN traffic to be dropped in affected async crypto configurations.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Review is recommended for systems using AH with ESN and async crypto or hardware crypto engines. The issue is network-triggerable in that configuration, but the supported impact is availability only.

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

Patch: xfrm: ah: account for ESN high bits in async callbacks [ Upstream
Commit: 0555d4f526232b3c9e3afbcd490c0c0793aefec6
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0555d4f526232b3c9e3afbcd490c0c0793aefec6

Changed files:
  net/ipv4/ah4.o
  net/ipv6/ah6.o
  net/ipv4/ah4.c
  net/ipv6/ah6.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=0555d4f526232b3c9e3afbcd490c0c0793aefec6

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

The original Linux kernel CVE announcement for CVE-2026-46193 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46193

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:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 5.9

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: YES
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).