[CVE-2026-53282][LOW] x86/kexec: Push kjump return address even for non-kjump kexec

[CVE-2026-53282][LOW] x86/kexec: Push kjump return address even for non-kjump kexec

[AL-KERNEL]

CVE: CVE-2026-53282
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: x86/kexec: Push kjump return address even for non-kjump kexec
Commit: b0bd7a850e1f082560959707dbf57b0402071646
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b0bd7a850e1f082560959707dbf57b0402071646
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53282
Analysis date: Fri, 26 Jun 2026 16:20:26 -0400
ActionableScore: 0
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
A non-kjump x86 kexec transition can fail because kexec-tools purgatory expects a return address word on the stack, causing a fault and denial of service for the kexec operation, but exploitation requires host administrative kexec privileges.

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

The original Linux kernel CVE announcement for CVE-2026-53282 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53282

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: LOW
Manual review required: NO

A detailed explanation of the methodology and priority rules is included
at the end of this message.

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-53282	LOW	CHECK	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H';CWE-665;CWE-703;CWE-754;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.4';DESCR 'The x86 kexec path can fail during a normal non-kjump kexec because the purgatory code from kexec-tools expects a return address word on the stack even when preserve-context kjump is not used. If that word is missing, purgatory may fault while checking whether kexec_jump_back_entry should be set, causing the kexec transition to fail. For the CVSS the PR:H is used because triggering this path normally requires administrative kexec privileges such as CAP_SYS_BOOT or root access. The issue is not network reachable and is not triggered by packet traffic or an unprivileged local interface. Impact is denial of service limited to failed kexec or reboot transition, with no evidence of confidentiality impact, integrity impact, UAF, OOB write, or privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 0)  SKIP CVE-2026-53282  SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	OOB DANGER SIMPLEFIX KERNEL_PANIC_PLUS_UAF HARDWARE  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	-	-	checked

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

ActionableScore=0

## 1. ActionableScore

* Conservative score: 0
* Paranoid score: 0
* Final recommended bucket: **Ordinary Moderate / Low-like**

## 2. Signal breakdown

* Reliable kernel crash / strong DoS: +1
  The purgatory code may fault during a non-kjump kexec transition because it expects a return address word on the stack.
* Requires admin/root/CAP_SYS_BOOT in typical deployments: -2
  Triggering kexec normally requires root or CAP_SYS_BOOT on the host.
* Rare or difficult-to-reach subsystem/configuration: -1
  This is limited to the kexec transition path, not a common syscall, network, filesystem, or packet-processing path.
* No memory corruption: +0
  The patch does not indicate UAF, double-free, OOB write, arbitrary write, object lifetime corruption, or page-cache corruption.
* No confidentiality or integrity impact: +0
  The observed effect is failed kexec transition, not data disclosure or privilege escalation.

Score is floored at 0.

## 3. Reachability analysis

The bug is reachable only by initiating a kexec path. In normal deployments this requires administrative privileges such as root or CAP_SYS_BOOT. Containers and user namespaces usually do not provide meaningful access to host kexec, and lockdown or distro policy may restrict it further. There is no realistic network trigger and no unprivileged local interface shown by the patch.

## 4. Severity interpretation

This behaves like a privileged local reliability or availability issue, not an Important-class vulnerability. The realistic impact is failure of a kexec reboot or crash-recovery transition. Theoretical memory corruption is not supported by the patch context, because the issue is an expected stack word missing for purgatory detection logic rather than attacker-controlled overwrite, UAF, or stale object reuse.

## 5. One-sentence report phrase

A non-kjump x86 kexec transition can fail because kexec-tools purgatory expects a return address word on the stack, causing a fault and denial of service for the kexec operation, but exploitation requires host administrative kexec privileges.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

This can be auto-closed for security triage unless the environment treats kexec failure as operationally critical. There is no supported LPE, memory corruption, or remote exposure signal.

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

Patch: x86/kexec: Push kjump return address even for non-kjump kexec
Commit: b0bd7a850e1f082560959707dbf57b0402071646
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b0bd7a850e1f082560959707dbf57b0402071646

Commit description:

The version of purgatory code shipped by kexec-tools attempts to look above
the top of its stack to find a return address for a kjump, even in a non-kjump
kexec.

After the commit in Fixes: the word above the stack might not be there,
leading to a fault (which is at least now caught by my exception-handling code
in kexec).

That commit fixed things for the actual kjump path, but no longer
"gratuitously" pushes the unused return address to the stack in the non-kjump
path. Put that *back* in the non-kjump path, to prevent purgatory from
crashing when trying to access it.

Fixes: 2cacf7f ("x86/kexec: Fix stack and handling of re-entry point for ::preserve_context")
Reported-by: Rohan Kakulawaram <rohanka@google.com>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
Tested-by: Rohan Kakulawaram <rohanka@google.com>
Cc: <stable@kernel.org>
Link: https://patch.msgid.link/32d627134143ffd957891cb697138e839c623211.camel@infradead.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  arch/x86/kernel/relocate_kernel_64.S

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=b0bd7a850e1f082560959707dbf57b0402071646

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

The original Linux kernel CVE announcement for CVE-2026-53282 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53282

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:H/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 4.4

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: unknown
  Paranoid ActionableScore: 0

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

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).