[CVE-2026-46033][IMPORTANT] crypto: authencesn - reject short ahash digests during instance creation

[CVE-2026-46033][IMPORTANT] crypto: authencesn - reject short ahash digests during instance creation

[AL-KERNEL]

CVE: CVE-2026-46033
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: crypto: authencesn - reject short ahash digests during instance creation
Commit: b69933e97efea238ebbfcf70c2b1be1cd03f13e3
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b69933e97efea238ebbfcf70c2b1be1cd03f13e3
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46033
Analysis date: Wed, 27 May 2026 15:59:43 -0400
ActionableScore: 8
ActionableScore lower bound: 6
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-46033 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46033

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.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-46033	IMPORTANT	CHECK	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-787;CWE-125;*CWE-20;CWE-754;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7.8';DESCR 'authencesn can inherit an invalid default authsize when the selected ahash has a digest size from 1 to 3 bytes. AF_ALG can then exercise the ESN encrypt or decrypt path with a too short tag, while that path still moves 4 bytes of high order sequence number data at the end of the authenticated data, causing an out of bounds access. For the CVSS the PR:L is used because a local user with access to AF_ALG can select the affected crypto construction and trigger the operation without full administrator privileges. The issue is not network reachable by itself. Impact is at least local denial of service via kernel memory access fault, with confidentiality and integrity impact retained in the paranoid score because the bug is an out of bounds access in a user controlled crypto data path.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 8) 	MAYBE	OOB INIT LINUS KPANIC  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=8
ActionableScoreLower=6

1. ActionableScore
* Conservative score: 6
* Paranoid score: 8
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

2. Signal breakdown
* Local unprivileged trigger: +1. A local user with AF_ALG access can instantiate the affected authencesn construction and exercise the AEAD operation.
* Local unprivileged high-control kernel data-plane API: +1. AF_ALG gives user space fine-grained control over crypto algorithm selection, buffers, tags, and operation parameters.
* Generic memory corruption / OOB access: +2. The commit explicitly states that too-short authsize can make the ESN path hit an out-of-bounds access.
* Reliable kernel crash / strong DoS: +1. An OOB access in the crypto data path can plausibly fault or crash the kernel.
* Availability impact realistic: +1. Local DoS is the minimum realistic impact.
* Paranoid confidentiality impact: +1. OOB access in a user-controlled crypto path may expose adjacent kernel data depending on direction and buffer layout.
* Paranoid integrity impact: +1. The ESN path moves 4 bytes at the authenticated-data tail, so a too-short tag may create an OOB write or corruption concern, although a controlled overwrite primitive is not proven.

3. Reachability analysis
The issue is local, not network reachable by itself. A user needs access to AF_ALG and to the affected crypto template combination such as authencesn with an ahash digest size of 1..3 bytes. This does not normally require full administrator privileges on systems exposing AF_ALG to unprivileged users. Containers may matter if AF_ALG sockets are available inside the container, because the vulnerable code still executes in the host kernel.

4. Severity interpretation
This is more serious than ordinary Moderate because it is an OOB access reachable through a high-control local kernel API. The realistic demonstrated impact is local kernel crash or memory access fault. The paranoid interpretation is Strong Important candidate because user-controlled crypto buffer handling plus OOB access may plausibly affect confidentiality or integrity, even though the patch does not prove arbitrary write or a full LPE chain.

5. One-sentence report phrase
A local AF_ALG user can create an authencesn instance with an invalid short default authsize and trigger ESN tail handling with a too-short tag, causing an out-of-bounds kernel access and possible DoS or memory corruption.

6. Manual review recommendation
MANUAL CHECK REQUIRED. This is a local high-control AF_ALG path with explicit OOB access, so it should not be auto-closed even without a demonstrated privilege escalation exploit.

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

Patch: crypto: authencesn - reject short ahash digests during instance creation
Commit: b69933e97efea238ebbfcf70c2b1be1cd03f13e3
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b69933e97efea238ebbfcf70c2b1be1cd03f13e3

Commit description:

authencesn requires either a zero authsize or an authsize of at least
4 bytes because the ESN encrypt/decrypt paths always move 4 bytes of
high-order sequence number data at the end of the authenticated data.

While crypto_authenc_esn_setauthsize() already rejects explicit
non-zero authsizes in the range 1..3, crypto_authenc_esn_create()
still copied auth->digestsize into inst->alg.maxauthsize without
validating it.  The AEAD core then initialized the tfm's default
authsize from that value.

As a result, selecting an ahash with digest size 1..3, such as
cbcmac(cipher_null), exposed authencesn instances whose default
authsize was invalid even though setauthsize() would have rejected the
same value.  AF_ALG could then trigger the ESN tail handling with a
too-short tag and hit an out-of-bounds access.

Reject authencesn instances whose ahash digest size is in the invalid
non-zero range 1..3 so that no tfm can inherit an unsupported default
authsize.

Fixes: f15f05b ("crypto: ccm - switch to separate cbcmac driver")
Cc: stable@kernel.org
Reported-by: Yifan Wu <yifanwucs@gmail.com>
Reported-by: Juefei Pu <tomapufckgml@gmail.com>
Co-developed-by: Yuan Tan <yuantan098@gmail.com>
Signed-off-by: Yuan Tan <yuantan098@gmail.com>
Suggested-by: Xin Liu <bird@lzu.edu.cn>
Tested-by: Yuhang Zheng <z1652074432@gmail.com>
Reviewed-by: Eric Biggers <ebiggers@kernel.org>
Signed-off-by: Yucheng Lu <kanolyc@gmail.com>
Signed-off-by: Ren Wei <n05ec@lzu.edu.cn>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  crypto/authencesn.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=b69933e97efea238ebbfcf70c2b1be1cd03f13e3

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

The original Linux kernel CVE announcement for CVE-2026-46033 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46033

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:L/PR:L/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7.8

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: 6
  Paranoid ActionableScore: 8

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: YES
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).