* [CVE-2026-98485][MODERATE REGULAR] netfilter: ip6t_rt: fix zero-address non-strict match out-of-bounds read
@ 2026-10-24 12:07 21% AL-KERNEL
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From: AL-KERNEL @ 2026-10-24 12:07 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-98485
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: netfilter: ip6t_rt: fix zero-address non-strict match out-of-bounds read
Commit: 959d1829d1ce8b91b435b24a923b51bcc8897090
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=959d1829d1ce8b91b435b24a923b51bcc8897090
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98485
Analysis date: Sat, 24 Oct 2026 08:07:52 -0400
ActionableScore: 2
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO
Summary:
A malformed IPv6 routing-header match rule can cause packet processing to read beyond `ip6t_rt` and potentially panic the kernel, without a shown write or disclosure primitive.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98485 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98485
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: NO
A detailed explanation of the methodology and priority rules is included
at the end of this message.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2026-98485 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-98485 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=0 LEGACY=MODERATE RESULT=DIFF (final Legacy and Aegis differ; FINAL: MODERATE, Aegis: MODERATE_KPANIC) 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-125;*CWE-20;CWE-129;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.9';DESCR 'A zero address IP6T_RT_FST_NSTRICT rule can let rt_mt6 increment i beyond addrnr and eventually read beyond the fixed rtinfo addrs array while processing matching addresses from an IPv6 Routing Header. The demonstrated primitive is an out of bounds read used only for address comparison, with no supported write primitive or direct disclosure path. For the CVSS the PR:N value reflects packet based triggering after a vulnerable rule is installed, although creating that rule normally requires CAP_NET_ADMIN. AC:H reflects the uncommon rule state and the need for crafted matching routing addresses. Impact is normally limited to a warning or failed match, but KASAN, UBSAN, or an inaccessible adjacent address can produce a kernel panic and host denial of service. Automated impact decision path. The original SimpleNet classifier selected MODERATE_KPANIC. The primary LLM estimated paranoid CVSS 5.9 and the production ActionableScore returned 2 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were ActionableScore thresholds stage MODERATE_KPANIC to MODERATE because the ActionableScore threshold rule was applied. The legacy KP specialist has no review artifact for this run. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 and V41_INHERITED_KPANIC_PROMOTION_BLOCKED and MANUAL_REVIEW_REQUIRED. The independent weaker Aegis shadow evaluated CVSS 4.1 and ActionableScore 0 with primitive class CLASS_C and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. The models disagreed but the aggregation rules retained the production result. The final reported impact is MODERATE.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2) MAYBE REMOTE WRITE KASAN OOB NETFILTER NETWORK LINUS IPV6 PACKET DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 V41_INHERITED_KPANIC_PROMOTION_BLOCKED MANUAL_REVIEW_REQUIRED - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=2
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO
1. ActionableScore
* Raw base score: 2.
* Conservative score: 2; no floor or cap applied.
* Raw paranoid score: 2.
* Paranoid score: 2; no separate technically supported escalation.
* Final recommended bucket: **Ordinary Moderate**::
2. Signal breakdown
* +1 limited OOB read: `i` can exceed the 16-entry `rtinfo->addrs` array, and `ipv6_addr_equal()` reads beyond the structure.
* +1 plausible kernel crash/DoS: the commit reports KASAN/UBSAN warnings or panic from an inaccessible out-of-bounds address.
* No write, disclosure path, attacker-selected read result, UAF, authorization bypass, or corrupted active state is shown.
* No remote-reachability bonus: packet triggering requires a previously installed malformed netfilter rule, which is a material control-plane prerequisite.
* No extra availability point: panic and host DoS are the same consequence.
* NEW52/B5-R does not apply: this is an accumulating read index, not a confirmed heap OOB write followed by corrupted-state consumption.
* NEW53 and B4-PENDING do not apply: there is neither shared-backing modification nor a DENY-to-ALLOW authorization change.
3. Reachability analysis
A crafted IPv6 Routing Header can exercise the bad loop only after installation of a zero-address `IP6T_RT_FST_NSTRICT` rule. Rule creation normally requires CAP_NET_ADMIN, while a later packet sender may need no local privilege. The evidence does not establish which capability namespace governs the complete setup or whether all stages are available below host administration. Prior privileged configuration is therefore required, but the effective complete-trigger privilege remains unknown. No race or special hardware is involved.
4. Primitive and severity reading
The exact primitive is a read beyond a fixed address array, used only in address comparison. It can encounter poisoned or inaccessible memory and crash, but no bytes are returned to the attacker and no kernel state is modified. This is CLASS_C crash/invalid-read behavior, not CLASS_A/B corruption. Important-grade leverage is unsupported, so automatic Moderate handling remains permissible.
5. One-sentence report phrase
A malformed IPv6 routing-header match rule can cause packet processing to read beyond `ip6t_rt` and potentially panic the kernel, without a shown write or disclosure primitive.
6. Manual review advice
MANUAL CHECK RECOMMENDED
Confirm product-specific CAP_NET_ADMIN namespace scope and whether vulnerable rules can be provisioned for remotely reachable traffic.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: netfilter: ip6t_rt: fix zero-address non-strict match out-of-bounds read
Commit: 959d1829d1ce8b91b435b24a923b51bcc8897090
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=959d1829d1ce8b91b435b24a923b51bcc8897090
Commit description:
rt_mt6_check() permits rules to be configured with rtinfo->addrnr == 0
even when address matching (IP6T_RT_FST_MASK) is requested.
In the IP6T_RT_FST_NSTRICT path, rt_mt6() evaluates packet routing
addresses against rtinfo->addrs[i] and terminates backwards at the bottom
of the loop:
if (ipv6_addr_equal(ap, &rtinfo->addrs[i])) {
i++;
}
if (i == rtinfo->addrnr)
break;
When addrnr is 0, if the first packet address matches rtinfo->addrs[0],
i is incremented to 1. Because i is now strictly greater than addrnr (0),
the loop termination condition (i == rtinfo->addrnr) is bypassed and will
never be satisfied.
If a crafted IPv6 packet contains matching routing addresses, i will
advance past IP6T_RT_HOPS (16). The subsequent call to ipv6_addr_equal()
reads beyond struct ip6t_rt, triggering UBSAN/KASAN out-of-bounds warnings
or kernel panics.
Fix this by:
1. Rejecting rules in rt_mt6_check() where IP6T_RT_FST_MASK is set but
rtinfo->addrnr is zero.
2. In rt_mt6(), moving the termination condition (i < rtinfo->addrnr)
into the for-loop header condition and removing the backwards break
at the end of the loop body.
Fixes: 1da177e ("Linux-2.6.12-rc2")
Cc: [email protected]
Reported-by: Vega <[email protected]>
Suggested-by: Florian Westphal <[email protected]>
Assisted-by: LLM
Signed-off-by: Luxiao Xu <[email protected]>
Signed-off-by: Ren Wei <[email protected]>
Signed-off-by: Pablo Neira Ayuso <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
net/ipv6/netfilter/ip6t_rt.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=959d1829d1ce8b91b435b24a923b51bcc8897090
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98485 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98485
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:N/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: unknown
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: 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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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