[CVE-2026-98643][MODERATE REGULAR] bpf: Fix out-of-bounds read of rtt_min in sock_ops [ Upstream

[AL-KERNEL <alkernel@kernelcve.org>]

CVE: CVE-2026-98643
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: bpf: Fix out-of-bounds read of rtt_min in sock_ops [ Upstream
Commit: 0c796efa919f52f788c22c79d1f1b70321696b3d
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0c796efa919f52f788c22c79d1f1b70321696b3d
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98643
Analysis date: Mon, 19 Oct 2026 03:26:57 -0400
ActionableScore: 4
ActionableScore lower bound: 3
Actionable bucket: Actionable Moderate
Manual review required: YES

Summary:
A privileged or delegated sock_ops BPF program can read four bytes beyond a request_sock as tcp_sock.rtt_min and disclose adjacent kernel memory, including observed kernel pointer bits that may assist KASLR bypass.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-98643 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98643

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: YES

A detailed explanation of the methodology and priority rules is included
at the end of this message.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-98643	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98643 CHECK WITH IMPACT FROM ORIG NN LOW | 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:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N';CWE-125;*CWE-200;CWE-843;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:L/I:N/A:N';BEST CVSS score: '3.3';DESCR 'An out of bounds kernel memory read occurs because access to bpf_sock_ops.rtt_min can treat a request_sock as the larger tcp_sock without verifying that sk references a locked full TCP socket. A local actor able to load and attach a sock_ops BPF program can reach the tcp_conn_request path and obtain 32 bits of adjacent kernel memory. An observed value contained the high half of a kernel pointer, making the issue a concrete information disclosure that may assist KASLR bypass or another exploit chain. For the CVSS the PR:L value is used for the paranoid score because BPF and cgroup capabilities may be delegated to a restricted service or container without granting full host administration. Typical systems still require CAP_BPF and CAP_NET_ADMIN or equivalent control, which supports PR:H for the base score. Network traffic can activate the affected socket path, but the vulnerability is not independently remotely exploitable because local control of the BPF program and access to its result are required. The demonstrated impact is limited confidentiality loss. No write primitive, privilege escalation, or availability impact is established by the affected access path. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 3.3 and the production ActionableScore returned 4 with recommendation Actionable Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage LOW to MODERATE_KPANIC because the manual review requirement was applied. KP and FD specialist checks stage MODERATE_KPANIC to MODERATE because KP specialist did not establish a qualifying panic. The legacy KP specialist produced a review artifact and its decision was processed by the applicable KP rules. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK and DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP and V41_INHERITED_KPANIC_PROMOTION_BLOCKED and MANUAL_REVIEW_REQUIRED. The independent weaker Aegis shadow evaluated CVSS 2.3 and ActionableScore 0 with primitive class CLASS_C and manual review RECOMMENDED. 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 Actionable Moderate (with actual score 4)	MAYBE	REMOTE OOB BPF LEAK LINUS  INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP V41_INHERITED_KPANIC_PROMOTION_BLOCKED MANUAL_REVIEW_REQUIRED	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=4
ActionableScoreLower=3
PrimitiveClass=CLASS_B
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw conservative score: 3
* Conservative score: 3
* Raw paranoid score: 4
* Paranoid score: 4
* No floor or cap changed either score.
* Final recommended bucket: **Actionable Moderate**::

2. Signal breakdown

Conservative positive signals:

* +1 weak or indirect corruption candidate. The context rewrite performs a concrete 32-bit OOB read by interpreting a live `request_sock` as the larger `tcp_sock`.
* +1 confidentiality plausible. The value is returned to the BPF program and can be stored or otherwise observed. This is a real disclosure path rather than an internal-only invalid read.
* +1 practical consequence chain. The supplied reproducer reaches `BPF_SOCK_OPS_RWND_INIT`, reads `rtt_min`, and has observed the high half of a kernel pointer.

Paranoid-only signal:

* +1 weak exploitation leverage. The observed kernel pointer bits can assist KASLR bypass or another exploit chain, although the fixed four-byte read does not establish broad kernel disclosure.

Not awarded:

* No OOB-write, active-state corruption, B5-R, B3-PENDING, or V33/V34 write-chain signal exists.
* No UAF, controlled reclaim, arbitrary read, arbitrary write, callback influence, or privilege escalation is established.
* No remote-reachability bonus. Network traffic may activate `tcp_conn_request`, but a local BPF program is required to perform and retrieve the read.
* No local-unprivileged bonus because the complete BPF load and attach path below host-admin privilege is unresolved.
* No crash or availability point is supported.
* No authorization-bypass or B4-PENDING signal exists.

3. Reachability analysis

The attacker must load a `BPF_PROG_TYPE_SOCK_OPS` program, attach it to an applicable cgroup, arrange for the `tcp_conn_request()` path to invoke the program, and extract the returned value. Typical deployments gate loading and attachment through `CAP_BPF`, `CAP_NET_ADMIN`, or equivalent BPF and cgroup management rights.

The supplied evidence does not establish whether all capability checks are satisfiable in an attacker-created user or network namespace. Delegation to a restricted service or container is credible but not confirmed for the complete sequence. Therefore both host-admin and namespace-scoped privilege requirements remain unknown.

A remote TCP peer can help generate the socket event but cannot exploit the disclosure independently without control of the locally attached BPF program. No special hardware or race timing is required.

4. Primitive and severity interpretation

The exact primitive is a fixed-width four-byte heap or slab OOB read from memory beyond a live `request_sock`. The JIT-generated access loads from the offset of `tcp_sock.rtt_min.s[0].v` without first checking `is_locked_tcp_sock`.

This is a live-object type and bounds mismatch, not a UAF or stale-storage operation. The value reaches attacker-controlled BPF execution, and an actual partial kernel pointer was observed. The demonstrated consequence is limited kernel-information disclosure.

The read address and width are fixed relative to `sk`. There is no evidence of arbitrary address selection, a write primitive, host crash, or direct privilege escalation. The patch therefore supports CLASS_B rather than CLASS_A. The partial pointer leak merits mandatory review as possible KASLR-bypass assistance, but the current evidence is insufficient for an Important candidate.

Auto-downgrade is disallowed because automatically closing the issue would discard a confirmed user-visible kernel-memory disclosure with observed pointer data. This does not imply Important severity.

5. One-sentence report phrase

A privileged or delegated sock_ops BPF program can read four bytes beyond a request_sock as tcp_sock.rtt_min and disclose adjacent kernel memory, including observed kernel pointer bits that may assist KASLR bypass.

6. Manual review recommendation

MANUAL CHECK REQUIRED

The disclosure is concrete and externally observable by the BPF program, but the complete capability boundary and practical value of repeated fixed-offset reads require product-specific review.

7. Call-site confidence

Call-site confidence: high

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UPSTREAM PATCH SUMMARY
======================================================================

Patch: bpf: Fix out-of-bounds read of rtt_min in sock_ops [ Upstream
Commit: 0c796efa919f52f788c22c79d1f1b70321696b3d
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0c796efa919f52f788c22c79d1f1b70321696b3d

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=0c796efa919f52f788c22c79d1f1b70321696b3d

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DETAILED REPORT METHODOLOGY
======================================================================

The original Linux kernel CVE announcement for CVE-2026-98643 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98643

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:L/I:N/A:N
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
  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: 3
  Paranoid ActionableScore: 4

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 alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).