[CVE-2026-64208][MODERATE 7.0] crypto/krb5, rxrpc: Fix lack of pre-decrypt/pre-verify length checks [ Upstream

[CVE-2026-64208][MODERATE 7.0] crypto/krb5, rxrpc: Fix lack of pre-decrypt/pre-verify length checks [ Upstream

[AL-KERNEL]

CVE: CVE-2026-64208
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: crypto/krb5, rxrpc: Fix lack of pre-decrypt/pre-verify length checks [ Upstream
Commit: 585f9f6aef5c4542ac9d6ec45cd7dbc7df9af3ff
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=585f9f6aef5c4542ac9d6ec45cd7dbc7df9af3ff
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64208
Analysis date: Fri, 24 Jul 2026 11:53:35 -0400
ActionableScore: 6
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
AF_RXRPC with RxGK could process too-short secured DATA packets without prechecking krb5 checksum, confounder, and payload lengths, allowing a remote peer to reach crypto processing with invalid offsets and causing at least remote DoS with limited C/I impact possible in the paranoid case.

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

The original Linux kernel CVE announcement for CVE-2026-64208 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64208

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: 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-2026-64208	MODERATE	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H';*CWE-20;CWE-125;CWE-190;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '8.6';DESCR 'AF_RXRPC with RxGK can process DATA packets through the krb5 verify or decrypt path without first proving that the secured blob is long enough for the krb5 checksum, confounder, and minimum RxGK payload. A remote peer can send a too-short RxGK protected DATA packet so that computed offsets and lengths become invalid before crypto processing. For the CVSS the PR:N is used because the paranoid scenario only requires network reachability to an AF_RXRPC endpoint using RxGK and does not require local code execution on the target. The issue is network reachable when RxGK secured rxrpc traffic is accepted by the target, although real exposure is usually limited to AFS or rxrpc deployments rather than general Internet facing services. Impact is at least remote denial of service and in the worst defensible case may include limited confidentiality or integrity impact from invalid length handling around skb and crypto buffers.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)  SKIP CVE-2026-64208 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: 9d1d2b59341f58126a69b51f9f5f8ccb9f12e54a YES  NO NO unknown 	MAYBE	INIT SKB PACKET  INCREASED_TO_HIGH_BASED_ON_GUESSCVSS8.5PLUS KPANIC DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN7	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=6
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 6
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Remote reachable / network-triggerable: +2
  AF_RXRPC DATA packets secured with RxGK are protocol input and can be supplied by a remote peer when an RxGK-enabled rxrpc endpoint is reachable.

* Memory corruption, weak/indirect corruption candidate: +1
  The bug is missing length validation before krb5 verify/decrypt processing. The patch prevents too-short blobs from producing invalid offset/length calculations. This supports possible invalid read or malformed buffer handling, but not a proven OOB write, UAF, or arbitrary write.

* Memory layout invariant restoration: +1
  The fix restores consistency between secure blob length, checksum/confounder length, data offset, and minimum payload length before skb crypto processing.

* Availability impact realistic: +1
  Malformed packets reaching crypto processing can plausibly cause protocol failure, WARN/Oops, or crash-like DoS depending on downstream handling.

* Rare/configuration-dependent exposure: -1
  RxGK over AF_RXRPC is not a general default Internet-facing protocol path. Real exposure is likely limited to AFS/rxrpc deployments using RxGK.

Paranoid additions:

* Confidentiality impact plausible: +1
  Invalid length handling before verify/decrypt may plausibly lead to limited OOB read or unintended buffer interpretation, but no direct disclosure primitive is shown.

* Integrity impact plausible: +1
  The encrypted path reaches in-place skb crypto processing after length-derived offset updates. This is enough for manual-review concern, but not enough to classify as strong corruption.

Not applied:

* No strong memory corruption +2. The patch does not show UAF, double free, OOB write, arbitrary write, type confusion, or refcount takeover.
* No Dirty-Pipe-like/shared-page bonus. The provided diff does not prove externally owned page-cache or COW bypass.
* No privilege escalation bonus. No LPE path is demonstrated.

## 3. Reachability analysis

A remote rxrpc peer can potentially trigger the vulnerable path by sending too-short RxGK-protected DATA packets to a target that accepts RxGK-secured AF_RXRPC traffic. No local code execution on the victim is needed in that scenario. Namespaces are not the main factor here because the interesting trigger is protocol input, not a local privileged control plane. The path is not broadly default-exposed like TCP core or netfilter packet processing. It depends on AF_RXRPC plus RxGK being used, commonly in AFS-like environments.

Call-site confidence: high. The patch shows the affected krb5 helpers and their rxgk verify/decrypt callers.

## 4. Severity interpretation

This is more than an ordinary Moderate because it is remotely triggerable protocol input with missing pre-crypto length validation and possible invalid offset/length handling. It is not a clear Important-class memory corruption issue from the patch alone because there is no demonstrated write primitive, UAF, object replacement, or privilege-escalation chain. The conservative interpretation is a remote DoS or malformed-buffer handling bug. The paranoid interpretation is Actionable Moderate because limited C/I impact from invalid read or crypto/skb buffer misuse is technically defensible and should not be auto-closed without review.

## 5. One-sentence report phrase

AF_RXRPC with RxGK could process too-short secured DATA packets without prechecking krb5 checksum, confounder, and payload lengths, allowing a remote peer to reach crypto processing with invalid offsets and causing at least remote DoS with limited C/I impact possible in the paranoid case.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: network-reachable protocol input reaches crypto/skb processing with missing length checks, and the patch changes helper semantics plus rxgk call sites. The evidence does not prove strong memory corruption, but the class is sensitive enough to require manual review rather than auto-close.

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

Patch: crypto/krb5, rxrpc: Fix lack of pre-decrypt/pre-verify length checks [ Upstream
Commit: 585f9f6aef5c4542ac9d6ec45cd7dbc7df9af3ff
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=585f9f6aef5c4542ac9d6ec45cd7dbc7df9af3ff

Changed files:
  crypto/krb5.rst
  crypto/krb5/krb5_api.c
  include/crypto/krb5.h
  include/trace/events/rxrpc.h
  net/rxrpc/rxgk.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=585f9f6aef5c4542ac9d6ec45cd7dbc7df9af3ff

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

The original Linux kernel CVE announcement for CVE-2026-64208 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64208

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:H
  The Best / paranoid CVSS vector: AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 8.6

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: 6

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).