[CVE-2025-68313][MODERATE REGULAR] x86/CPU/AMD: Add RDSEED fix for Zen5

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

CVE: CVE-2025-68313
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: x86/CPU/AMD: Add RDSEED fix for Zen5
Commit: e980de2ff109dacb6d9d3a77f01b27c467115ecb
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e980de2ff109dacb6d9d3a77f01b27c467115ecb
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2025-68313
Analysis date: Wed, 09 Sep 2026 02:44:29 -0400
ActionableScore: 4
ActionableScore lower bound: 3
Actionable bucket: Borderline / manual review recommended
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-2025-68313 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2025-68313

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 REGULAR
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-2025-68313	MODERATE	https://www.kernelcve.org/list/?q=CVE-2025-68313 CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N';CWE-338;CWE-331;CWE-682;CWE-338;CWE-331;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:N';BEST CVSS score: '4.8';DESCR 'A Zen5 RDSEED hardware issue can make 16 bit and 32 bit RDSEED variants return zero while incorrectly reporting success with CF set. If the kernel advertises RDSEED on affected microcode, kernel or user space consumers may treat these outputs as valid entropy and generate weaker random values for cryptographic use. For the CVSS the PR:N is used in the paranoid model because a remote party may need no account on the target if an exposed service relies on affected random output for keys, nonces, or other security material. The issue is not a memory corruption bug and is not a direct packet processing vulnerability. Impact is mainly possible weakening of confidentiality and integrity for workloads that depend on RDSEED, with practical exposure limited to affected AMD Zen5 systems and unfixed microcode.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 4) 	MAYBE	INIT HARDWARE LINUS TEST 	-	-	checked

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

ActionableScore=4
ActionableScoreLower=3
PrimitiveClass=NONE
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=REQUIRED
AutoDowngradeAllowed=NO

1. ActionableScore

* Raw conservative score: 3
* Conservative score: 3
* Raw paranoid score: 4
* Paranoid score: 4
* Final recommended bucket: **Borderline / manual review recommended**::

No floor or cap was applied. The paranoid score is used as the final ActionableScore because the issue affects a security-sensitive entropy source and the downstream cryptographic impact is workload-dependent.

2. Signal breakdown

Positive signals:

* +2: Security-sensitive entropy correctness defect. RDSEED16/RDSEED32 on affected Zen5 microcode can return zero while incorrectly signaling success with CF=1, so consumers may treat bad output as valid entropy.
* +1 conservative: Potential downstream cryptographic impact. Direct RDSEED consumers may generate weaker seeds, nonces, keys, or other security material, but no specific exploit chain is supplied.
* +1 paranoid: Remote-service impact is technically plausible if an exposed service generates security material on an affected system and depends materially on RDSEED output.

Negative or non-awarded signals:

* RealUAF not awarded. No use-after-free, stale object, refcount issue, OOB access, or memory corruption is established.
* CLASS_A not awarded. There is no controlled corruption, authorization bypass, COW ownership violation, arbitrary write, or demonstrated privilege escalation.
* Reliable kernel crash not awarded. The patch is about entropy correctness, not panic or DoS.
* Confidentiality and integrity bonuses were not separately awarded as direct consequences because no concrete protected data disclosure, unauthorized modification, or complete exploit chain is supplied.
* Remote reachable +2 not awarded. The hardware fault can affect remote-facing workloads, but attacker traffic does not directly reach a vulnerable packet-processing operation.
* Physical-only or rare hardware penalty not applied. Zen5 is hardware-specific, but the issue concerns a CPU feature on affected systems, not a rare peripheral or physical-access-only device.
* AutoDowngradeAllowed=NO because cryptographic entropy issues can be underestimated by patch-only analysis and need product-specific review of RDSEED consumers.

3. Reachability analysis

The affected behavior is present on AMD Zen5 systems with vulnerable microcode revisions where the kernel would otherwise advertise RDSEED. There is no normal attacker-triggered kernel API primitive comparable to a syscall UAF or network parser bug. A local process can execute RDSEED directly if the CPU feature is exposed, and kernel or userspace components may consume RDSEED as an entropy input.

HostAdminRequired is UNKNOWN because exploitation is not a classic privileged operation. The attacker may not need host administrator privileges if the security consequence arises through an application or service that generates cryptographic material on the affected host. However, the supplied evidence does not prove a complete below-host-admin exploit chain.

NamespaceScopedPrivilege is NO because namespaces are not relevant to the RDSEED CPU feature exposure. Prior privileged setup is not the main issue, but affected CPU model and insufficient microcode are prerequisites. Race repeatability is not relevant.

I cannot perform live web search from this environment. The commit explicitly references AMD-SB-7055, and supplied context should be checked against that bulletin for exact affected models, microcode revisions, and vendor severity.

4. Primitive and severity interpretation

The exact primitive is incorrect hardware entropy reporting: RDSEED16/RDSEED32 may return zero while reporting success. This is not active structured kernel-object corruption and not fixed stale storage. There is no cleanup/destructor UAF and no concrete repeated release/refcount operation.

PrimitiveClass is NONE under this scoring taxonomy because no kernel corruption, lifetime violation, ownership violation, authorization bypass, or memory safety primitive is established. The demonstrated consequence is possible weakening of random values. The speculative consequence is weakened cryptographic material in workloads that rely too strongly on RDSEED.

ImportantCandidate is NO because no memory corruption, LPE, boundary bypass, or demonstrated protected-resource compromise is established. ManualReview is REQUIRED because entropy-source defects can have product-specific confidentiality and integrity impact that is not visible from the kernel patch alone. AutoDowngradeAllowed is NO because automatically closing a cryptographic entropy correctness issue without checking affected workloads and AMD-SB-7055 would risk a false-negative triage result.

Likely operational severity is Borderline to Actionable Moderate depending on deployment. Systems that do not use affected Zen5 CPUs or already have fixed microcode are not exposed. Systems with cryptographic workloads that directly trust RDSEED16/RDSEED32 deserve manual review.

5. One-sentence report phrase

Affected AMD Zen5 systems may expose broken RDSEED16 and RDSEED32 behavior where zero can be returned while success is signaled, potentially weakening cryptographic entropy for kernel or user space consumers that rely on RDSEED.

6. Manual review recommendation

MANUAL CHECK REQUIRED

Check AMD-SB-7055, affected Zen5 model and stepping, installed microcode revision, whether the kernel disables RDSEED on unfixed systems, and whether security-sensitive workloads directly consume RDSEED for keys, nonces, seeds, or session material.

7. Call-site confidence

Call-site confidence: medium

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

Patch: x86/CPU/AMD: Add RDSEED fix for Zen5
Commit: e980de2ff109dacb6d9d3a77f01b27c467115ecb
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e980de2ff109dacb6d9d3a77f01b27c467115ecb

Commit description:

There's an issue with RDSEED's 16-bit and 32-bit register output
variants on Zen5 which return a random value of 0 "at a rate inconsistent
with randomness while incorrectly signaling success (CF=1)". Search the
web for AMD-SB-7055 for more detail.

Add a fix glue which checks microcode revisions.

  [ bp: Add microcode revisions checking, rewrite. ]

Cc: stable@vger.kernel.org
Signed-off-by: Gregory Price <gourry@gourry.net>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20251018024010.4112396-1-gourry@gourry.net
[ bp: 6.12 backport: use the alternative microcode version checking. ]
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  arch/x86/kernel/cpu/amd.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=e980de2ff109dacb6d9d3a77f01b27c467115ecb

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

The original Linux kernel CVE announcement for CVE-2025-68313 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2025-68313

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:L/I:L/A:N
  The Best / paranoid CVSS vector: AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N
  The Best / paranoid CVSS score: 4.8

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: 3
  Paranoid ActionableScore: 4

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: NO
Published priority for this report (same as in Subject): MODERATE REGULAR

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).