[CVE-2026-74564][LOW] netfilter: xt_hashlimit: validate hashtable supports XT_HASHLIMIT_RATE_MATCH [ Upstream

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

CVE: CVE-2026-74564
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: netfilter: xt_hashlimit: validate hashtable supports XT_HASHLIMIT_RATE_MATCH [ Upstream
Commit: 24683fea1f06bd3bd2707b99460e859bc6464c22
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=24683fea1f06bd3bd2707b99460e859bc6464c22
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74564
Analysis date: Sat, 15 Aug 2026 10:35:28 -0400
ActionableScore: 2
ActionableScore lower bound: 0
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
`xt_hashlimit allowed incompatible reuse of a named hashlimit table across rate match and non rate match rules, which could read an uninitialized burst field and cause incorrect firewall matching decisions, but exploitation requires local netfilter rule control and no memory corruption or privilege escalation primitive is shown.`

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-74564 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74564

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.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-74564	LOW	CHECK WITH IMPACT FROM ORIG NN IMPORTANT	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:L';CWE-908;*CWE-457;*CWE-20;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:L/A:N';BEST CVSS score: '4.4';DESCR 'xt_hashlimit can reuse a named hashlimit table across multiple rules even though XT_HASHLIMIT_RATE_MATCH uses a different dsthash_ent union layout. If one rule creates the table in one mode and another rule reuses it in the other mode, the rate match path can read an uninitialized burst field and make packet matching decisions from inconsistent state. For the CVSS the PR:L is used for the paranoid score because a local process with delegated CAP_NET_ADMIN or container network administration may be able to install iptables rules, even though full host firewall administration is often PR:H in practice. The issue is not directly network reachable because packets only exercise a ruleset that was already installed through the local control plane. Impact is mainly limited integrity risk for firewall policy correctness and possible limited availability impact for traffic handling, not a kernel memory corruption or privilege escalation primitive.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 1)	YES	REMOTE LOCK SIMPLEFIX NETFILTER  LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=2
ActionableScoreLower=0

## 1. ActionableScore

* Conservative score: 0
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate / Low-like**::

## 2. Signal breakdown

Conservative signals:

* Integrity impact plausible: +1
  Mixed reuse of the same xt_hashlimit hashtable with different `XT_HASHLIMIT_RATE_MATCH` semantics can make packet matching decisions depend on an uninitialized `burst` field.
* Broad/common subsystem exposure: +1
  Netfilter/iptables is broadly deployed, although this specific `xt_hashlimit` mode and shared-table configuration is not default.
* Requires CAP_NET_ADMIN in typical deployments: -2
  The vulnerable state is created through iptables/netfilter rule installation, which normally requires administrative network privileges.

Conservative total: 0

Paranoid adjustment:

* Limited availability impact plausible: +1
  Incorrect hashlimit state may cause traffic handling disruption or unexpected filtering behavior, but no kernel crash is shown.
* Delegated CAP_NET_ADMIN interpretation: penalty reduced from -2 to -1
  In container or delegated network administration scenarios, the attacker may not be full host root.

Paranoid total: 2

Not awarded:

* No remote-triggerable score. Packets only exercise a ruleset that must already be installed through the local control plane.
* No generic memory corruption score. The patch describes uninitialized scalar field access, not UAF, OOB write, double free, arbitrary write, or type confusion.
* No LPE score. There is no supported reclaim, overwrite, callback, refcount, or privilege escalation primitive.
* No reliable kernel crash score. The commit does not describe panic, Oops, BUG, or a reliable system-wide DoS.

## 3. Reachability analysis

The bug is triggered by creating or reusing named `xt_hashlimit` tables across rules with incompatible `XT_HASHLIMIT_RATE_MATCH` mode semantics. In normal host deployments this requires `CAP_NET_ADMIN`, so the conservative privilege model is privileged local control-plane access.

Namespaces and containers can lower practical privilege in some environments if untrusted users are granted network administration inside a namespace. However, the impact is typically confined to the ruleset and traffic governed by that namespace unless the delegated control plane affects host firewall policy.

The path is not directly network reachable. Network packets may observe or exercise the inconsistent hashlimit state after misconfiguration, but they do not create the vulnerable state by themselves.

Call-site confidence: high, because the patch shows the `.checkentry` validation path and the hashtable mode consistency check.

## 4. Severity interpretation

This behaves like an ordinary Moderate or Low-like issue, not an Important-class kernel vulnerability. The realistic impact is incorrect firewall policy behavior due to uninitialized union field interpretation. The theoretical concern is limited integrity impact for packet matching correctness, but the patch does not support memory corruption, privilege escalation, sensitive data disclosure, or reliable host crash.

## 5. One-sentence report phrase

`xt_hashlimit allowed incompatible reuse of a named hashlimit table across rate match and non rate match rules, which could read an uninitialized burst field and cause incorrect firewall matching decisions, but exploitation requires local netfilter rule control and no memory corruption or privilege escalation primitive is shown.`

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

This can be auto-closed for most environments because it is a privileged netfilter control-plane validation issue with limited policy-integrity impact and no demonstrated memory corruption, LPE, info leak, or reliable kernel crash. Manual review is only useful if the product treats delegated `CAP_NET_ADMIN` or container firewall management as an important untrusted boundary.

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

Patch: netfilter: xt_hashlimit: validate hashtable supports XT_HASHLIMIT_RATE_MATCH [ Upstream
Commit: 24683fea1f06bd3bd2707b99460e859bc6464c22
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=24683fea1f06bd3bd2707b99460e859bc6464c22

Changed files:
  net/netfilter/xt_hashlimit.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=24683fea1f06bd3bd2707b99460e859bc6464c22

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

The original Linux kernel CVE announcement for CVE-2026-74564 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74564

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:L/A:N
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:L
  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: 0
  Paranoid ActionableScore: 2

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).