* [CVE-2026-89562][LOW] ip6_gre: fix hardware header length for NBMA tunnels
@ 2026-09-12 2:25 21% AL-KERNEL
0 siblings, 0 replies; 1+ results
From: AL-KERNEL @ 2026-09-12 2:25 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-89562
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: ip6_gre: fix hardware header length for NBMA tunnels
Commit: 8bfe746afee38dd6e4348ddcd22d554789dbb9ff
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8bfe746afee38dd6e4348ddcd22d554789dbb9ff
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89562
Analysis date: Fri, 11 Sep 2026 22:25:35 -0400
ActionableScore: 1
ActionableScore lower bound: unknown
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-2026-89562 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89562
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-2026-89562 LOW https://www.kernelcve.org/list/?q=CVE-2026-89562 CHECK WITH IMPACT FROM ORIG NN MODERATE 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:L';CWE-682;CWE-665;CWE-754;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '3.3';DESCR 'ip6_gre NBMA tunnels used an incorrect hardware header length calculation when header_ops was set, because the lower device hardware header length was accumulated into dev hard_header_len instead of being kept as extra headroom. This can make the tunnel device expose an incorrect header length and may cause MTU or packet handling problems for affected IPv6 GRE NBMA tunnel configurations. For the CVSS the PR:L paranoid value is used only for environments where an untrusted local user has delegated network administration rights or can create IPv6 GRE devices in a network namespace. The issue is not directly network reachable because it depends on local tunnel configuration rather than remote packet contents. Impact is limited denial of service or connectivity degradation for the affected tunnel, with no evidence of memory corruption, information disclosure, or privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1) YES REMOTE SIMPLEFIX NETWORK HARDWARE IPV6 DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 NO NO checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=1
PrimitiveClass=NONE
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES
1. ActionableScore
* Raw conservative score: 1
* Conservative score: 1
* Raw paranoid score: 1
* Paranoid score: 1
* Final recommended bucket: **Ordinary Moderate**::
No floor or cap changed the score.
2. Signal breakdown
Positive signals:
* +1 limited availability or functionality impact: incorrect `hard_header_len` and `needed_headroom` accounting can plausibly cause MTU, packet handling, or tunnel connectivity problems for affected IPv6 GRE NBMA tunnel configurations.
Negative or non-awarded signals:
* No memory corruption awarded: the patch changes header length accounting only.
* No UAF awarded: no stale object, freed object, RCU lifetime issue, double release, or refcount mutation is established.
* No reliable kernel crash awarded: the evidence supports tunnel misconfiguration or packet handling degradation, not panic or host-wide fatal fault.
* No confidentiality or integrity signal awarded: no information leak, unauthorized write, ownership violation, or security-boundary bypass is shown.
* No remote reachability awarded: remote packets are not shown to trigger the vulnerable operation independently of local tunnel configuration.
* No namespace-scoped privilege bonus awarded: IPv6 GRE tunnel management is capability-gated, but the supplied evidence does not prove that the complete trigger is available to an ordinary user through attacker-created namespaces.
* No host-admin penalty applied as a hard fact: CAP_NET_ADMIN is expected for tunnel configuration, but the evidence does not fully resolve whether the relevant operation must be host/init namespace admin in all evaluated deployments.
3. Reachability analysis
The vulnerable behavior is reached through local IPv6 GRE tunnel configuration and route-derived device setup, not directly through incoming packet contents. Creating or modifying such tunnel devices normally requires CAP_NET_ADMIN through rtnetlink or equivalent network administration interfaces.
The complete privilege boundary is not fully established from the supplied patch alone. It may be host network administration in a normal host deployment, or a delegated or namespace-scoped network administration context in containerized environments. Therefore HostAdminRequired is UNKNOWN and NamespaceScopedPrivilege is UNKNOWN.
No prior special hardware, unusual boot mode, or rare physical device requirement is established. No race is involved. The issue is deterministic once the affected tunnel type and configuration path are used.
4. Primitive and severity interpretation
The exact primitive is incorrect length and headroom accounting for IPv6 GRE NBMA tunnel devices. The lower device hardware header length was incorrectly accumulated into the tunnel device hard header length when `header_ops` was present, while the lower device header should instead be retained as needed headroom. For `ip6gretap` and `ip6erspan`, the fixed Ethernet hardware header length should remain unchanged.
This is a logic or initialization/accounting bug, not an active structured UAF, fixed stale storage UAF, double release, refcount corruption, OOB access, arbitrary write, or authorization bypass. The demonstrated consequence is limited availability or connectivity degradation for affected tunnel configurations. Stronger consequences such as host crash, privilege escalation, information disclosure, or remote compromise are not supported by the patch.
PrimitiveClass is NONE because no meaningful corruption, ownership, lifetime, authorization, or security-boundary primitive is established. ImportantCandidate is NO because the issue lacks memory corruption, cross-boundary impact, or unresolved exploitation leverage. AutoDowngradeAllowed is YES because this is an ordinary low-actionability networking correctness issue with limited impact.
Likely operational severity: Low-like to ordinary Moderate, mainly relevant for systems that use affected IPv6 GRE NBMA tunnel configurations.
5. One-sentence report phrase
An IPv6 GRE NBMA tunnel could expose an incorrect hardware header length due to wrong lower-device header accounting, causing possible MTU or packet handling issues for locally configured tunnels but no demonstrated memory corruption, privilege escalation, information disclosure, or direct remote trigger.
6. Manual review recommendation
NO MANUAL CHECK NEEDED
Reason: the patch supports only a local configuration-dependent tunnel accounting bug with limited availability impact and no concrete corruption, lifetime, authorization, or boundary-bypass primitive.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: ip6_gre: fix hardware header length for NBMA tunnels
Commit: 8bfe746afee38dd6e4348ddcd22d554789dbb9ff
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8bfe746afee38dd6e4348ddcd22d554789dbb9ff
Commit description:
ip6gre_tnl_link_config_route() accumulates the lower device's hardware
header length into dev->hard_header_len whenever header_ops is set. This
is incorrect for both users of header_ops.
ip6gretap and ip6erspan have a fixed Ethernet hardware header length.
For an NBMA ip6gre tunnel, ip6gre_header() creates only the GRE header,
the optional FOU or GUE header, and the outer IPv6 header. The lower
device header is headroom needed later, not part of the tunnel device's
hardware header.
Keep the lower device header in needed_headroom. Set hard_header_len to
the tunnel header length only for ARPHRD_IP6GRE devices with header_ops,
and leave the fixed Ethernet header length unchanged for tap and erspan
devices.
Fixes: 832ba59 ("net: ip6_gre: set dev->hard_header_len when using header_ops")
Cc: [email protected]
Suggested-by: Ido Schimmel <[email protected]>
Signed-off-by: Zhiling Zou <[email protected]>
Reviewed-by: Ido Schimmel <[email protected]>
Link: https://patch.msgid.link/64b46542bbe1701f07702aaa50273e2a87903db5.1786542637.git.zhilinz@nebusec.ai
Signed-off-by: Paolo Abeni <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
net/ipv6/ip6_gre.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=8bfe746afee38dd6e4348ddcd22d554789dbb9ff
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-89562 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89562
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:N/A:L
The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
The Best / paranoid CVSS score: 3.3
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: 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).
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