[CVE-2026-74315][MODERATE 7.0] lockd: Avoid hashing uninitialized bytes in nlm4svc_lookup_file() [ Upstream

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

CVE: CVE-2026-74315
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: lockd: Avoid hashing uninitialized bytes in nlm4svc_lookup_file() [ Upstream
Commit: 686c2434f9f16b87aeed18d76cc562df9f2695ab
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=686c2434f9f16b87aeed18d76cc562df9f2695ab
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74315
Analysis date: Sat, 15 Aug 2026 16:48:53 -0400
ActionableScore: 5
ActionableScore lower bound: unknown
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A remote NLMv4 client can cause lockd to hash uninitialized tail bytes of short file handles, making identical handles map to different lock-state buckets and potentially breaking NFS lock enforcement.

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

The original Linux kernel CVE announcement for CVE-2026-74315 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74315

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-2026-74315	MODERATE	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:N/I:L/A:L';*CWE-457;CWE-908;CWE-665;BEST CVSS score: '4.8';DESCR 'NFS lockd can hash uninitialized tail bytes when an NLMv4 client sends a file handle shorter than LOCKD_FH_HASH_SIZE. The same wire file handle can then map to different nlm_file buckets across requests, causing nlm_lookup_file to miss existing lock state and making NLM lock enforcement unreliable for affected files. For the CVSS the PR:N is used because the trigger is a network protocol request to lockd and does not require a local user account on the target, although real deployments usually restrict NFS and lockd access to trusted storage networks or exported clients. The issue is network reachable but the attack complexity is high because reliable impact depends on short file handles and on the residual argument buffer contents from earlier requests. Impact is limited integrity and availability for network lock state correctness. There is no clear evidence of memory corruption, information disclosure, kernel crash, or privilege escalation.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)  SKIP CVE-2026-74315 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: 3de744ee4e4557da0d63be8a97ad44b4dad58912 YES  NO NO unknown 	MAYBE	DEADLOCK DISK INIT SIMPLEFIX  KPANIC INCREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN5	-	-	checked

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

ActionableScore=5

## 1. ActionableScore

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

## 2. Signal breakdown

* **Remote reachable / network-triggerable: +2**
  NLMv4 lockd is a network service path. A remote NFS or NLM client can provide a short file handle.

* **Integrity impact plausible: +1**
  The same wire file handle can hash into different `nlm_file` buckets, causing lock-state lookup misses. This can make NLM lock enforcement unreliable.

* **Availability impact realistic: +1**
  Failed lock-state lookups can break expected locking behavior and disrupt NFS clients or applications relying on network locks.

* **Important filesystem/storage path: +1**
  The affected code is in NFS lockd file-lock tracking, which is security and correctness relevant for shared storage.

* **Practical exploit chain strongly implied: +1**
  The commit directly describes the chain: short handle -> uninitialized tail bytes affect hash -> bucket mismatch -> `nlm_lookup_file()` misses existing state -> lock-state lookup failure.

* **Hard or unreliable conditions: -1**
  Reliable triggering depends on short file handles and residual argument-buffer contents from previous requests. This makes impact less deterministic.

No memory corruption, UAF, OOB write, privilege escalation, or information disclosure primitive is supported by the patch.

## 3. Reachability analysis

The bug can be triggered by a remote NLMv4 client that can send requests to lockd. No local account on the target is required, so PR:N is reasonable for CVSS-style reachability. In real deployments, NFS and lockd are usually restricted to trusted storage networks or exported-client sets, so public Internet exposure is uncommon. Namespaces and containers do not materially reduce the requirement because the relevant path is the host lockd network service. The path is not a generic Internet-facing default service, but it is realistic in NFS server environments.

Call-site confidence: **high**. The patch and commit message show both the hash consumer `file_hash()` and the producer `nlm4svc_lookup_file()`.

## 4. Severity interpretation

This behaves like an **actionable Moderate**, not an Important-class memory corruption issue. The security concern is correctness of remote lock-state tracking, with plausible limited integrity and availability impact. There is no evidence of kernel memory corruption, attacker-controlled overwrite, kernel crash, information disclosure, or privilege escalation. However, because it is network reachable and affects NFS lock semantics, it should not be auto-closed without human review.

## 5. One-sentence report phrase

A remote NLMv4 client can cause lockd to hash uninitialized tail bytes of short file handles, making identical handles map to different lock-state buckets and potentially breaking NFS lock enforcement.

## 6. Manual review recommendation

**MANUAL CHECK REQUIRED**

Manual review is required because the issue is network reachable and can affect NFS lock-state integrity, even though it does not show memory corruption or privilege escalation.

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

Patch: lockd: Avoid hashing uninitialized bytes in nlm4svc_lookup_file() [ Upstream
Commit: 686c2434f9f16b87aeed18d76cc562df9f2695ab
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=686c2434f9f16b87aeed18d76cc562df9f2695ab

Changed files:
  fs/lockd/lockd.h
  fs/lockd/svc4proc.c
  fs/lockd/svcsubs.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=686c2434f9f16b87aeed18d76cc562df9f2695ab

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

The original Linux kernel CVE announcement for CVE-2026-74315 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74315

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: Not available
  The Best / paranoid CVSS vector: AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:L
  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: unknown
  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).