* [CVE-2026-98383][MODERATE 7.0] bpf: Disallow bpf_skb_pull_data() for LWT_SEG6LOCAL [ Upstream
@ 2026-10-10 2:33 21% AL-KERNEL
0 siblings, 0 replies; 1+ results
From: AL-KERNEL @ 2026-10-10 2:33 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-98383
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: bpf: Disallow bpf_skb_pull_data() for LWT_SEG6LOCAL [ Upstream
Commit: 0f38472a2aa8704a6b514c0dfa9c32f3672b8f32
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0f38472a2aa8704a6b514c0dfa9c32f3672b8f32
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98383
Analysis date: Fri, 09 Oct 2026 22:33:42 -0400
ActionableScore: 5
ActionableScore lower bound: unknown
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-2026-98383 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98383
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-2026-98383 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-98383 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=2 LEGACY=MODERATE_KPANIC RESULT=SAME (legacy and Aegis reconciliation agree; DECISION: both 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:H/I:H/A:H';*CWE-416;*CWE-787;CWE-825;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7.8';DESCR 'An LWT_SEG6LOCAL BPF program can invalidate its cached SRH with bpf_lwt_seg6_adjust_srh() and then call bpf_skb_pull_data(), which may reallocate skb head and leave the per CPU SRH pointer dangling. Post program SRH validation can then write through the stale pointer, creating a write after free style memory corruption primitive in the host kernel. For the CVSS the PR:L value is used for the paranoid score because a reduced capability container root or service with delegated BPF and network administration capabilities may be able to load and attach the required program without full host root privileges. This is not directly network reachable because remote packets cannot install the unsafe BPF program, although packets can execute it after local configuration. Impact is at least a local denial of service and may include privilege escalation or host kernel compromise if the stale write can be shaped reliably.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5) MAYBE REMOTE BPF SIMPLEFIX SKB HARDWARE IPV6 KPANIC INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=5
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO
1. ActionableScore
* Raw conservative score: 5
* Conservative score: 5
* Raw paranoid score: 5
* Paranoid score: 5
* No floor or cap changed either score. The BPF control-plane exception was evaluated but does not reduce this to a cleanup-only UAF because the stale pointer is written through during active packet processing.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::
2. Signal breakdown
* +2 Real UAF / lifetime violation. `bpf_skb_pull_data()` may reallocate and release the old `skb->head`, while the cached per-CPU SRH pointer continues to reference that old allocation.
* +1 Reliable kernel crash / strong DoS. Post-program validation writes through the dangling SRH pointer, making a kernel fault or memory corruption realistic.
* +1 Attacker-influenced active-object state and repeatable lifetime manipulation. An accepted LWT_SEG6LOCAL program controls the unsafe helper sequence and can execute it repeatedly on packets.
* +1 Structured stale-object leverage. The stale reference points into an actively interpreted SRH, and the later operation writes through it rather than merely reading it or immediately rejecting it.
* No separate strong-leverage bonus. Controlled reclaim, arbitrary target selection, directed write, callback control, and attacker-selected replacement contents are not demonstrated.
* No extra Availability point. The possible crash and the post-free write describe the same failure mechanism.
* No Confidentiality or Integrity bonus. The stale write is concrete, but no protected victim, disclosure path, arbitrary write, or completed privilege-escalation chain is established.
* No remote-reachability bonus. Network packets can execute an already attached program, but cannot independently load and attach the unsafe BPF program.
* No privilege penalty. BPF loading and LWT_SEG6LOCAL attachment are privilege-gated, but the supplied evidence does not resolve whether the complete operation requires host-admin-equivalent authority or can be completed with delegated or namespace-scoped capabilities.
* B5-R does not apply. There is no retry-accumulated index or offset.
* B3-PENDING does not apply. No shared file-backed or COW backing violation is established.
* B4-PENDING does not apply. No authorization decision changes from DENY to ALLOW.
3. Reachability analysis
The initiating actor must load an LWT_SEG6LOCAL BPF program, attach it to the relevant IPv6 Segment Routing local action, and execute the unsafe sequence consisting of `bpf_lwt_seg6_adjust_srh()` followed by `bpf_skb_pull_data()`. Loading and attachment normally involve BPF and network-administration capability checks, but the supplied patch does not establish which user namespace governs every required stage.
Ordinary unprivileged reachability is therefore not established. Host-admin-equivalent privilege is also not positively established, because delegated BPF and network-management services may exist and the complete capability chain is not shown. `HostAdminRequired` and `NamespaceScopedPrivilege` remain UNKNOWN.
No special hardware, firmware, race, or narrow timing window is required. Once the program has been accepted and attached, the helper sequence is deterministic and can be exercised repeatedly. Remote traffic alone is insufficient because privileged local control-plane setup is required first.
4. Primitive and severity interpretation
The exact primitive is a post-reallocation write through a dangling pointer into the old `skb->head` allocation. This is a real write-after-free-style lifetime violation, not a NULL dereference, passive metadata mismatch, or validation-only issue.
The stale target is part of actively processed structured packet state. The vulnerable use occurs in the data path during post-program SRH validation, not primarily during cleanup, destruction, or namespace teardown. There is no repeated release or refcount mutation on the same reference.
This is CLASS_B rather than CLASS_A. A concrete post-free write exists, but the evidence does not establish controlled reclaim, arbitrary or directed kernel write, callback influence, protected-object corruption, or privilege escalation.
The demonstrated practical consequences are kernel memory corruption and plausible host DoS. Privilege escalation or host compromise remains possible only if an analyst can show useful allocator reuse or sufficient control over the stale write and adjacent victim. That unresolved leverage makes this an Important candidate and prevents automatic downgrade, but does not justify scoring it as a proven high-impact exploit.
5. One-sentence report phrase
An LWT_SEG6LOCAL BPF program can force skb head reallocation while retaining a cached SRH pointer, causing post-program validation to write through freed kernel memory and requiring manual exploitation-leverage review.
6. Manual review recommendation
MANUAL CHECK REQUIRED
The patch establishes an active data-path post-free write, while control over reclaimed memory, write contents, privilege scope, and escalation potential remains unresolved.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: bpf: Disallow bpf_skb_pull_data() for LWT_SEG6LOCAL [ Upstream
Commit: 0f38472a2aa8704a6b514c0dfa9c32f3672b8f32
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0f38472a2aa8704a6b514c0dfa9c32f3672b8f32
Changed files:
net/core/filter.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=0f38472a2aa8704a6b514c0dfa9c32f3672b8f32
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98383 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98383
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:H/PR:H/UI:N/S:U/C:L/I:L/A:H
The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
The Best / paranoid CVSS score: 7.8
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: 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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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