* [CVE-2026-98234][LOW] net/sched: hhf: cap hh_flows_limit at change time
@ 2026-10-09 6:34 21% AL-KERNEL
0 siblings, 0 replies; 1+ results
From: AL-KERNEL @ 2026-10-09 6:34 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-98234
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: net/sched: hhf: cap hh_flows_limit at change time
Commit: 7adfd0a42174b85c6bd678858ecd6674f403f336
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=7adfd0a42174b85c6bd678858ecd6674f403f336
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98234
Analysis date: Fri, 09 Oct 2026 02:34:32 -0400
ActionableScore: 1
ActionableScore lower bound: 0
Actionable bucket: Ordinary Moderate
Manual review required: NO
Summary:
No one-sentence report phrase was found.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98234 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98234
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-2026-98234 LOW https://www.kernelcve.org/list/?q=CVE-2026-98234 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=0 LEGACY=LOW RESULT=DIFF TEMP_DISTANCE_MERGE_SKIP=AEGIS_NO_POSITIVE_SEVERITY_EVIDENCE (independent Legacy and Aegis differ; FINAL: LOW, Aegis: MODERATE_KPANIC) 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:N/A:H';CWE-770;**CWE-400;CWE-789;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.5';DESCR 'The HHF qdisc accepted an unrestricted hh_flows_limit value, allowing the configured flow limit to approach the full U32 range. Each newly classified heavy hitter flow can then cause a fixed size GFP_ATOMIC kernel allocation, so sustained spoofed traffic can make allocation growth outpace flow expiration and cleanup. For the CVSS the PR:L value is used because reliable triggering requires CAP_NET_ADMIN, but that capability may be available inside a user created network namespace and does not necessarily imply full host administrator privileges. The required configuration is performed through the local tc and netlink control path, so AV:L is more appropriate than a network vector even though generated or received traffic is used to drive repeated allocations. The demonstrated primitive is resource exhaustion rather than memory corruption. Base impact is A:L because substantial repeated traffic is required, while the paranoid assessment uses A:H because sustained abuse can potentially create host wide kernel memory pressure or OOM conditions. No UAF, OOB access, information disclosure, arbitrary write, or credible privilege escalation primitive is present in the affected path.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1) MAYBE REMOTE DANGER NETWORK QDISC DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=1
ActionableScoreLower=0
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=YES
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES
1. ActionableScore
* Raw conservative score: 0.
* Conservative score: 0.
* Raw paranoid score: 1.
* Paranoid score: 1.
* No floor or cap was applied.
* Final recommended bucket: **Ordinary Moderate**::
2. Signal breakdown
Conservative signals:
* +1 Concrete resource-amplification defect. An unrestricted `hh_flows_limit` permits repeated fixed-size `GFP_ATOMIC` allocations for newly classified heavy-hitter flows.
* -1 Reduced namespace-scoped privilege. The demonstrated setup requires `CAP_NET_ADMIN` in a user namespace, which is below host-admin-equivalent privilege but remains a privileged control-plane capability.
* Total: 0.
Paranoid additional signal:
* +1 Reliable strong DoS concern. Sustained spoofed traffic after installing the unsafe limit can make allocation growth exceed flow expiration and plausibly cause host-wide memory pressure, allocation failures, or OOM.
* Total: 1.
Important signals not awarded:
* No concrete persistent leak point. The allocations belong to active flows and are not shown to survive flow expiration or qdisc destruction permanently.
* No OOB read or write is established.
* No UAF, stale reference, refcount corruption, or ownership violation is established.
* No arbitrary or directed write is demonstrated.
* No confidentiality or integrity consequence is demonstrated.
* No direct remote-reachability bonus is awarded because local `tc` and netlink configuration is a prerequisite.
* No extra Availability point is awarded because memory exhaustion and resulting DoS are the same consequence.
* B5-R does not apply. There is no retry-accumulated index, confirmed heap OOB write, or later consumption of OOB-corrupted structured state.
3. Reachability analysis
The demonstrated trigger requires a caller with `CAP_NET_ADMIN` in a user namespace to configure an HHF qdisc with an extremely large `hh_limit`. The commit explicitly identifies this namespace-scoped capability as sufficient for the relevant qdisc operation, so host-administrator privilege is not required for the supplied reproduction.
After configuration, sustained traffic containing many distinct or spoofed flows drives allocations. Traffic alone cannot create the vulnerable state because it cannot set `hh_flows_limit`. The complete security-relevant setup is therefore local control-plane configuration followed by data-plane traffic, not a directly remote attack.
No special hardware, boot parameter, race, or narrow timing window is required. The evidence does not establish that every ordinary user can create the required user and network namespaces on every affected deployment, so ordinary unprivileged reachability is not separately scored.
4. Primitive and severity interpretation
The exact primitive is attacker-configured removal of an effective resource ceiling, followed by repeated fixed-size kernel allocations as new heavy-hitter flows are observed. This is a resource-exhaustion logic bug rather than memory corruption.
There is no active or fixed stale object, no lifetime violation, and no repeated release or refcount mutation. The demonstrated consequence is potentially unbounded kernel-memory growth under sustained traffic. Host-wide OOM or severe network degradation is plausible, but privilege escalation and confidentiality or integrity effects are unsupported.
The issue is CLASS_C because its security-relevant behavior is availability loss without an independently useful corruption primitive. `ImportantCandidate=NO` because neither B5-R nor another Important-preserving primitive is established. `AutoDowngradeAllowed=YES` because the remaining risk is bounded to resource exhaustion requiring namespace-scoped control-plane privilege and sustained traffic.
Likely operational severity is Low to Moderate depending on whether untrusted users receive usable user and network namespaces with `CAP_NET_ADMIN`.
5. One-sentence report phrase
An attacker with namespace-scoped CAP_NET_ADMIN can configure an excessive HHF flow limit and use sustained spoofed traffic to drive unbounded kernel allocations, potentially causing memory-exhaustion denial of service without evidence of memory corruption or privilege escalation.
6. Manual review recommendation
NO MANUAL CHECK NEEDED
The patch establishes a resource-exhaustion issue only, while the supplied B5-R profile is inapplicable because no heap OOB write, retry-accumulated offset, or corrupted-state consumption exists.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: net/sched: hhf: cap hh_flows_limit at change time
Commit: 7adfd0a42174b85c6bd678858ecd6674f403f336
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=7adfd0a42174b85c6bd678858ecd6674f403f336
Commit description:
hhf_change() stores TCA_HHF_HH_FLOWS_LIMIT with no upper bound. A huge
hh_flows_limit lets each new heavy-hitter flow pass the
hh_flows_current_cnt check in alloc_new_hh() and forces a fixed-size
kzalloc(GFP_ATOMIC) per flow under spoofed traffic, for unbounded memory
growth.
Bound the attribute with NLA_POLICY_MAX() at 2*HH_FLOWS_CNT (the
hhf_init() default) and report the rejected value via extack. The
deprecated nested parse is kept: legacy tc does not set NLA_F_NESTED on
TCA_OPTIONS. Configs relying on hh_limit above the default were relying
on unbounded, unsafe behaviour and are not supported going forward.
hhf_init() also ran hhf_change() before setting the default
hh_flows_limit, so a user-supplied hh_limit at add time was clobbered
back to 2048. Set the default before hhf_change() so the configured
value sticks.
This is a follow-up to commit eb56a49 ("net/sched: hhf: clamp
quantum in change and init paths"), which bounded the quantum of the
same qdisc; the hh_flows_limit bound is the remaining unbounded knob of
that series' scope.
Conditions to recreate the bug: CAP_NET_ADMIN in a user namespace;
tc qdisc change dev X root hhf hh_limit 4294967295 succeeds and the
value is echoed by tc qdisc show, unbounding heavy-hitter flow
allocations; also tc qdisc add dev X root hhf hh_limit 500 stores 2048
instead of 500.
Fixes: 10239ed ("net-qdisc-hhf: Heavy-Hitter Filter (HHF) qdisc")
Cc: [email protected]
Reported-by: Sashiko (gemini) <[email protected]>
Closes: https://sashiko.dev/#/patchset/[email protected]
Reviewed-by: Victor Nogueira <[email protected]>
Tested-by: hybris <[email protected]>
Signed-off-by: Jamal Hadi Salim <[email protected]>
Reviewed-by: Simon Horman <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Paolo Abeni <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
net/sched/sch_hhf.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=7adfd0a42174b85c6bd678858ecd6674f403f336
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98234 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98234
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:L/UI:N/S:U/C:N/I:N/A:L
The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
The Best / paranoid CVSS score: 5.5
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: 1
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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
^ permalink raw reply [relevance 21%]
Results 1-1 of 1 | reverse | sort options + mbox downloads above
-- links below jump to the message on this page --
2026-10-09 6:34 21% [CVE-2026-98234][LOW] net/sched: hhf: cap hh_flows_limit at change time AL-KERNEL
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox