[CVE-2026-72247][MODERATE 7.0] netfilter: nf_conncount: fix zone comparison in tuple dedup

[CVE-2026-72247][MODERATE 7.0] netfilter: nf_conncount: fix zone comparison in tuple dedup

[AL-KERNEL]

CVE: CVE-2026-72247
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: netfilter: nf_conncount: fix zone comparison in tuple dedup
Commit: 82fc35e0da9a91db9a034f8311f18f77a599ae3f
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=82fc35e0da9a91db9a034f8311f18f77a599ae3f
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72247
Analysis date: Sat, 15 Aug 2026 21:15:43 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A zone direction mismatch in `nf_conncount` can cause connections from different conntrack zones to be deduplicated as the same tuple, allowing a remote peer to bypass connlimit accounting in affected netfilter configurations.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-72247 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72247

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-2026-72247	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:N/A:H';CWE-697;CWE-682;CWE-693;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:L';BEST CVSS score: '5.9';DESCR 'nf_conncount could incorrectly deduplicate entries from different conntrack zones because the zone direction bitmask was passed where an IP_CT_DIR_ORIGINAL style direction value was expected. In affected connlimit setups this can make different zones look equal when the original tuple matches, so a new connection may be treated as already counted and the connection limit can be undercounted. A remote peer may trigger the behavior by creating traffic that reaches a connlimit rule in a deployment using conntrack zones, but the scenario depends on zone configuration and matching tuples. For the CVSS the PR:N is used for the paranoid score because no local account is needed when the vulnerable firewall path is reachable by network traffic. The issue is network reachable only through packet filtering paths already configured by an administrator. Impact is mainly firewall limit policy bypass and possible availability impact from connlimit bypass, not memory corruption or privilege escalation.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	REMOTE NETFILTER RACE SKB LINUS TEST PACKET  KPANIC INCREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN5	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: **4**
* Paranoid score: **5**
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* **Remote reachable / network-triggerable: +2**
  A remote peer can potentially trigger the wrong conncount behavior by sending traffic through an already configured netfilter connlimit path using conntrack zones.

* **Common networking core path or packet-processing path: +1**
  The bug is in netfilter / conntrack packet-processing logic, specifically `nf_conncount`.

* **Integrity impact plausible: +1**
  The issue can cause connlimit policy bypass or undercounting across zones, which is a firewall policy integrity problem.

* **Availability impact realistic: +1**
  Bypassing connection limits can increase resource consumption or defeat DoS-limiting rules.

* **Hard / configuration-dependent trigger: -1**
  Exploitation depends on a specific ruleset using `nf_conncount` / connlimit with conntrack zones and suitable tuple overlap.

Conservative total: **4**

Paranoid additional interpretation:

* **Cross-boundary isolation / policy bypass: +1**
  In zone-based netfilter deployments, treating different conntrack zones as equal can bypass intended isolation between traffic domains or policy contexts.

Paranoid total: **5**

No memory corruption, UAF, OOB write, refcount misuse, or privilege escalation primitive is shown by the patch.

## 3. Reachability analysis

The bug is reachable through network traffic only when the host has netfilter connlimit rules backed by `nf_conncount` and conntrack zones. The attacker does not need a local account if they can send packets through the affected firewall path, so PR:N is reasonable for the network-triggered scenario. However, the configuration is not universal, and reliable triggering depends on zone setup and tuple matching behavior. Namespaces or containers mainly matter on the administrator side for configuring the rules, not for a remote packet sender.

Call-site confidence: **high**, because the changed code is directly in `__nf_conncount_add()` and the commit explains the deduplication decision path.

## 4. Severity interpretation

This behaves like an **actionable Moderate** rather than an Important-class kernel memory-corruption bug. The realistic impact is firewall connlimit undercounting, policy bypass, and possible availability degradation. There is no supported evidence of kernel memory corruption, information disclosure, arbitrary write, or local privilege escalation. The reason it should not be auto-closed is that it is network reachable in affected netfilter deployments and can defeat a security-relevant rate or connection limiting policy.

## 5. One-sentence report phrase

A zone direction mismatch in `nf_conncount` can cause connections from different conntrack zones to be deduplicated as the same tuple, allowing a remote peer to bypass connlimit accounting in affected netfilter configurations.

## 6. Manual review recommendation

**MANUAL CHECK REQUIRED**

Manual review is required because the issue is network reachable in configured firewall paths and can bypass a netfilter connection limiting policy, even though it is not a memory corruption or privilege escalation vulnerability.

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

Patch: netfilter: nf_conncount: fix zone comparison in tuple dedup
Commit: 82fc35e0da9a91db9a034f8311f18f77a599ae3f
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=82fc35e0da9a91db9a034f8311f18f77a599ae3f

Commit description:

The "already exists" dedup logic in __nf_conncount_add() decides
whether a connection has already been counted and can be skipped instead
of incrementing the connlimit count.  It compares the conntrack zone of a
list entry with the zone of the connection being added using
nf_ct_zone_id() and nf_ct_zone_equal(), passing conn->zone.dir or
zone->dir as the direction argument.

Those helpers take enum ip_conntrack_dir values: IP_CT_DIR_ORIGINAL is 0
and IP_CT_DIR_REPLY is 1.  However, zone->dir is a u8 bitmask:
NF_CT_ZONE_DIR_ORIG is 1, NF_CT_ZONE_DIR_REPL is 2 and
NF_CT_DEFAULT_ZONE_DIR is 3.  Passing that bitmask as the enum direction
shifts the meaning of every non-zero value.  An ORIG-only zone passes 1
and is tested as REPLY, while REPL-only and default zones pass 2 or 3 and
test bits beyond the valid direction range.  In those cases
nf_ct_zone_id() can fall back to NF_CT_DEFAULT_ZONE_ID instead of using
the real zone id, so different zones can be treated as equal and dedup
collapses to tuple equality alone.

nf_conncount stores and compares the original-direction tuple for a
connection.  If an skb already has an attached conntrack entry,
get_ct_or_tuple_from_skb() explicitly copies
ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple, regardless of the packet's
ctinfo.  Therefore the zone comparison in the tuple dedup path must use
IP_CT_DIR_ORIGINAL as well; the zone direction bitmask describes where a
zone id applies, not which direction this conncount tuple represents.

Fix the two dedup comparisons by passing IP_CT_DIR_ORIGINAL directly.
Do not special-case NF_CT_DEFAULT_ZONE_DIR and do not compare raw zone
ids: using the existing helpers with IP_CT_DIR_ORIGINAL preserves the
direction-aware NF_CT_DEFAULT_ZONE_ID fallback.  A default bidirectional
zone contains the ORIG bit, so it naturally returns the real zone id;
reply-only zones continue to fall back for original-direction tuple
comparisons.

Fixes: 21ba884 ("netfilter: nf_conncount: Fix garbage collection with zones")
Fixes: b36e452 ("netfilter: nf_conncount: fix garbage collection confirm race")
Cc: stable@vger.kernel.org
Reported-by: Yizhou Zhao <zhaoyz24@mails.tsinghua.edu.cn>
Reported-by: Yuxiang Yang <yangyx22@mails.tsinghua.edu.cn>
Reported-by: Ao Wang <wangao@seu.edu.cn>
Reported-by: Xuewei Feng <fengxw06@126.com>
Reported-by: Qi Li <qli01@tsinghua.edu.cn>
Reported-by: Ke Xu <xuke@tsinghua.edu.cn>
Assisted-by: Claude-Code:GLM-5.2
Signed-off-by: Yizhou Zhao <zhaoyz24@mails.tsinghua.edu.cn>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  net/netfilter/nf_conncount.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=82fc35e0da9a91db9a034f8311f18f77a599ae3f

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

The original Linux kernel CVE announcement for CVE-2026-72247 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72247

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:L/A:L
  The Best / paranoid CVSS vector: AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 5.9

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: 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).