* [CVE-2026-89783][MODERATE 7.0] xfrm6: fix out-of-bounds write in xfrm6_input_addr() when secpath is full [ Upstream
@ 2026-09-16 9:30 21% AL-KERNEL
0 siblings, 0 replies; 1+ results
From: AL-KERNEL @ 2026-09-16 9:30 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-89783
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: xfrm6: fix out-of-bounds write in xfrm6_input_addr() when secpath is full [ Upstream
Commit: 91fc387f63c00ddfb5221127a17bac97549a8343
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=91fc387f63c00ddfb5221127a17bac97549a8343
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89783
Analysis date: Wed, 16 Sep 2026 05:30:58 -0400
ActionableScore: 6
ActionableScore lower bound: 5
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES
Summary:
No one-sentence report phrase was found.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-89783 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89783
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.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2026-89783 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-89783 CHECK WITH IMPACT FROM ORIG NN IMPORTANT Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H';*CWE-787;CWE-193;*CWE-20;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '8.1';DESCR 'An out-of-bounds write in the IPv6/XFRM input path can occur because xfrm6_input_addr used an off by one depth check before appending a state pointer to the secpath xvec array. When the preserved secpath is already full, the receive path can re enter IPv6 input and the next address based XFRM lookup can write one pointer past the fixed xvec array. For the CVSS the PR:N is used because no local account on the target is required if the affected XFRM/IPsec receive path is reachable by crafted network traffic. The issue is network reachable only on systems with relevant IPv6 XFRM or IPsec configuration and requires a specific nested or reinjected packet processing state, so AC:H is appropriate. Impact is at least remote denial of service via UBSAN warning or kernel panic. Because the primitive is a kernel out-of-bounds write of a pointer inside a security path object, the paranoid score treats confidentiality and integrity impact as possible and this should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 6) YES REMOTE WRITE KASAN OOB NETWORK LINUS IPV6 KPANIC PACKET DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH NO NO checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=6
ActionableScoreLower=5
PrimitiveClass=CLASS_B
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
1. ActionableScore
* Raw conservative score: 5
* Conservative score: 5. No floor or cap applied.
* Raw paranoid score: 6
* Paranoid score: 6. No floor or cap applied.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::
2. Signal breakdown
Conservative signals:
* +1: Constrained kernel out-of-bounds write. The patch establishes a real one-slot write past `sp->xvec[]`, but the written value is a kernel-derived `xfrm_state *` pointer and the target is a fixed adjacent location inside the `sec_path` allocation rather than an attacker-selected arbitrary address.
* +2: Network-triggerable packet-processing path. The vulnerable operation is in IPv6/XFRM receive processing and can be reached by crafted network traffic when the target has the relevant XFRM/IPsec configuration.
* +1: Reliable kernel crash / strong DoS. UBSAN_BOUNDS reports the out-of-bounds access and `panic_on_warn` can turn this into a kernel panic.
* +1: Meaningful active-state corruption concern. The corrupted object is not passive metadata only. It is an active security path object used by XFRM packet processing, so the effect should not be auto-closed as warning-only.
Paranoid signals:
* +2: Stronger interpretation of the OOB write. For the paranoid score, the established primitive is treated as an attacker-reachable kernel pointer write into active packet/security-path state, although arbitrary write or controlled target selection is not demonstrated.
* +2: Network-triggerable packet-processing path.
* +1: Reliable kernel crash / strong DoS.
* +1: Meaningful unresolved exploitation concern due to active XFRM/secpath state corruption.
Important non-awarded signals:
* RealUAF not awarded. No use-after-free or stale post-lifetime object use is established by this patch.
* Controlled reclaim not demonstrated.
* Arbitrary or directed kernel write not demonstrated.
* Confidentiality and integrity concrete impact not awarded as separate ActionableScore signals because no read-back, credential overwrite, authorization bypass, or controlled security-object modification is demonstrated.
* Extra Availability not awarded because the UBSAN warning / panic and kernel crash are the same DoS consequence.
* Race/timing penalty not awarded. This is an ordered state/bounds bug, not a narrow race.
* Host-admin penalty not awarded. The attacker does not need host-admin privileges if the affected XFRM/IPsec receive path is already exposed to crafted traffic.
* Rare-subsystem penalty not awarded. XFRM/IPsec configuration limits exposure, but the supplied evidence does not prove a rare or attacker-unreachable deployment prerequisite sufficient for a negative score.
3. Reachability analysis
The evaluated attacker is a remote network attacker that can send crafted IPv6 traffic to a system where the relevant XFRM/IPsec receive path is configured and reachable.
No local user account is required for the packet-triggered path described in the supplied context. Therefore `HostAdminRequired=NO`.
The issue is not primarily namespace-scoped. It is a network receive-path issue on the target host, so `NamespaceScopedPrivilege=NO`.
There is a prior configuration dependency: the target must use an affected IPv6 XFRM/IPsec scenario, including transport-mode receive reinjection with a preserved full secpath and an inner packet carrying a destination-options HAO option or type-2 routing header. This meaningfully increases practical specificity, but it is not the same as attacker-required host-admin privilege.
No special physical hardware is required. No hard race is established. The complexity comes from needing a specific protocol/state configuration rather than from a narrow timing window.
4. Primitive and severity interpretation
The exact primitive is an off-by-one kernel out-of-bounds write in `xfrm6_input_addr()`. When `sp->len == XFRM_MAX_DEPTH`, the old check fails to reject the full secpath and `sp->xvec[sp->len++] = x` writes one element past the six-entry `xvec[]` array.
This is not a UAF. It is a real kernel memory corruption primitive, but constrained: the index is fixed at one past the array and the payload is a kernel `xfrm_state *` pointer rather than arbitrary attacker bytes.
The object is active structured kernel state. `sec_path` and its `xvec[]` entries participate in XFRM/IPsec receive processing, so the corruption is more security-relevant than passive accounting damage. However, no controlled reclaim, arbitrary read/write, callback control, credential corruption, or demonstrated privilege escalation is established.
PrimitiveClass is `CLASS_B`: a real potentially exploitable kernel corruption primitive exists and exploitation-leverage analysis is required.
Demonstrated consequence is remote or network-adjacent denial of service through UBSAN warning and possible kernel panic. Speculative consequence is stronger memory-corruption impact if the adjacent corrupted state can be made security-relevant in a controlled way, but that is not proven by the supplied patch.
ImportantCandidate is `YES` because this is a network-reachable kernel OOB write into active XFRM state and should not be automatically downgraded to ordinary Moderate without manual review.
AutoDowngradeAllowed is `NO` because auto-closing would lose a concrete remote kernel corruption primitive with unresolved exploitation leverage, even though demonstrated impact is currently DoS.
Likely operational severity: actionable Moderate at minimum, with Strong Important review warranted for affected XFRM/IPsec deployments.
5. One-sentence report phrase
A network-reachable off-by-one bounds error in IPv6/XFRM secpath handling can write one `xfrm_state` pointer past the fixed `xvec` array when the secpath is already full, causing at least kernel crash DoS and requiring manual review because it is a real kernel out-of-bounds write in active packet security-path state.
6. Manual review recommendation
MANUAL CHECK REQUIRED
Reason: the patch establishes a concrete kernel OOB write reachable from network packet processing under affected XFRM/IPsec configuration, and the unresolved leverage of corrupting active `sec_path` state should not be auto-downgraded based only on the currently demonstrated crash.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: xfrm6: fix out-of-bounds write in xfrm6_input_addr() when secpath is full [ Upstream
Commit: 91fc387f63c00ddfb5221127a17bac97549a8343
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=91fc387f63c00ddfb5221127a17bac97549a8343
Changed files:
net/ipv6/xfrm6_input.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=91fc387f63c00ddfb5221127a17bac97549a8343
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-89783 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89783
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:L/I:L/A:H
The Best / paranoid CVSS vector: AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
The Best / paranoid CVSS score: 8.1
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: 5
Paranoid ActionableScore: 6
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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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