[CVE-2026-80738][MODERATE REGULAR] bpf: Check sk_state before sk_protocol in bpf_tcp_*_syncookie [ Upstream

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

CVE: CVE-2026-80738
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: bpf: Check sk_state before sk_protocol in bpf_tcp_*_syncookie [ Upstream
Commit: 23f682083aa3fbc0c49667818efd6979a8bc5ac2
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=23f682083aa3fbc0c49667818efd6979a8bc5ac2
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80738
Analysis date: Thu, 03 Sep 2026 05:40:13 -0400
ActionableScore: 3
ActionableScore lower bound: 2
Actionable bucket: Borderline Moderate, manual review recommended
Manual review required: YES

Summary:
bpf_tcp_gen_syncookie() and bpf_tcp_check_syncookie() could read sk_protocol before confirming a full TCP LISTEN socket, allowing a privileged local BPF program to trigger an invalid kernel read and possible DoS. For the CVSS the PR:L is appropriate when delegated BPF or network administration capability is sufficient, but typical deployments still require privileged BPF access.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-80738 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80738

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-2026-80738	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-80738 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:H';CWE-843;CWE-125;*CWE-20;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:H';BEST CVSS score: '5.5';DESCR 'bpf_tcp_gen_syncookie() and bpf_tcp_check_syncookie() could read sk sk_protocol before confirming that the supplied sock_common pointer refers to a full TCP LISTEN socket. A local BPF program can pass or receive a mini-socket style object where sk_state is valid but sk_protocol is a fullsock specific field, which can cause an invalid kernel read and potentially a crash. For the CVSS the PR:L is selected because triggering requires local ability to load or run the relevant BPF program, often through CAP_BPF, CAP_NET_ADMIN, or a delegated service context rather than remote packet access alone. The issue is not directly network reachable, although traffic may be used to drive the BPF hook after the program is installed. Impact is primarily denial of service via kernel crash. A limited confidentiality impact is kept only in the paranoid interpretation because the primitive is an invalid read without evidence of an arbitrary write or confirmed privilege escalation.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline Moderate, manual review recommended (with actual score 3)	YES	REMOTE BPF SIMPLEFIX 	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=3
ActionableScoreLower=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 3
* Final recommended bucket: **Borderline Moderate, manual review recommended**::

## 2. Signal breakdown

* Weak/indirect corruption candidate: +1. The helper accepts ARG_PTR_TO_BTF_ID_SOCK_COMMON but reads sk_protocol before proving that the object is a full socket. This is an invalid struct interpretation / wrong object field access.
* Reliable kernel crash / strong DoS: +1. The patch prevents dereferencing a fullsock-specific field on mini-socket objects, which can plausibly lead to an invalid kernel read and crash.
* Weak LPE concern, paranoid only: +1. This is not a proven LPE primitive, but BPF helper type handling and socket object confusion justify manual review in the paranoid score.
* Requires privileged BPF access in typical deployments: -2 conservative. Loading or attaching the relevant BPF program normally requires CAP_BPF, CAP_NET_ADMIN, CAP_SYS_ADMIN, root, or a privileged service context.
* Reduced-capability or delegated context adjustment: -1 paranoid. In some environments, container root, delegated CAP_BPF, delegated CAP_NET_ADMIN, or service-managed BPF may be less than full host root.

## 3. Reachability analysis

The bug is locally reachable through BPF helper use, not directly through unauthenticated network traffic. Network packets may help exercise the installed BPF program, but the attacker first needs the ability to load or run the relevant BPF program. In typical hardened product configurations where unprivileged BPF is disabled, this is privileged local attack surface. Namespace and container setups matter because delegated CAP_BPF or CAP_NET_ADMIN can make the practical privilege level closer to PR:L than full host-root, but this still is not PR:N.

Call-site confidence: high, because the affected helper checks and field access order are visible in the supplied patch.

## 4. Severity interpretation

This behaves more like a Moderate BPF type handling bug with possible local DoS than an Important-class vulnerability. The concrete primitive is an invalid read / wrong object interpretation, not UAF, OOB write, refcount takeover, callback control, or arbitrary write. Theoretical privilege escalation concern is weak and based only on BPF object type confusion risk, so it should not be scored as strong memory corruption without further evidence.

## 5. One-sentence report phrase

bpf_tcp_gen_syncookie() and bpf_tcp_check_syncookie() could read sk_protocol before confirming a full TCP LISTEN socket, allowing a privileged local BPF program to trigger an invalid kernel read and possible DoS. For the CVSS the PR:L is appropriate when delegated BPF or network administration capability is sufficient, but typical deployments still require privileged BPF access.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED. YES REQUIRES MANUAL CHECK.

Reason: BPF helper type handling and mini-socket versus full-socket interpretation deserve review, but current evidence supports invalid read / DoS rather than confirmed LPE.

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

Patch: bpf: Check sk_state before sk_protocol in bpf_tcp_*_syncookie [ Upstream
Commit: 23f682083aa3fbc0c49667818efd6979a8bc5ac2
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=23f682083aa3fbc0c49667818efd6979a8bc5ac2

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=23f682083aa3fbc0c49667818efd6979a8bc5ac2

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

The original Linux kernel CVE announcement for CVE-2026-80738 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80738

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:L/UI:N/S:U/C:L/I:N/A:H
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 5.5

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: 2
  Paranoid ActionableScore: 3

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).