[CVE-2026-64575][MODERATE 7.0] bpf: tcp: fix double sock release on batch realloc [ Upstream

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

CVE: CVE-2026-64575
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: bpf: tcp: fix double sock release on batch realloc [ Upstream
Commit: 9f27c4f0ae35b5390ce4f7a54d3501144e41a54d
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9f27c4f0ae35b5390ce4f7a54d3501144e41a54d
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64575
Analysis date: Wed, 05 Aug 2026 04:53:52 -0400
ActionableScore: 5
ActionableScore lower bound: 2
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A BPF TCP iterator realloc failure path can leave batch indexes pointing at cookie values instead of socket pointers, causing the stop path to treat cookies as `struct sock` objects and crash the kernel.

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ABOUT THIS REPORT
======================================================================

The original Linux kernel CVE announcement for CVE-2026-64575 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64575

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.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-64575	MODERATE	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';**CWE-476;*CWE-672;CWE-415;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.8';DESCR 'A BPF TCP iterator failure path can leave cur_sk and end_sk pointing at batch slots that no longer contain struct sock pointers. bpf_iter_tcp_put_batch first drops the socket references and rewrites the slots with socket cookies, but if bpf_iter_tcp_realloc_batch fails before resume runs, seq stop may call the put path again and treat those cookie values as socket pointers. This can reach __sock_gen_cookie with an invalid pointer and crash the kernel. For the CVSS the PR:L because triggering requires local ability to create or read a BPF TCP iterator, but it does not necessarily require full administrator control in environments where BPF access is delegated. The issue is not network reachable because it is triggered through a local BPF iterator read path rather than incoming TCP traffic. Impact is at least local denial of service via kernel panic and in worst case may allow limited confidentiality or integrity impact due to kernel pointer confusion, so it should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4)  SKIP CVE-2026-64575 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: cdec67a489d4fdae3e83e04fca0419136a83c4c2 YES  NO NO unknown 	MAYBE	REMOTE READ NULLPTR BPF LEAK UAF NETWORK 	-	-	checked

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ACTIONABLESCORE ANALYSIS
======================================================================

ActionableScore=5
ActionableScoreLower=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**

## 2. Signal breakdown

Conservative signals:

* Weak or indirect corruption candidate: +1. The bug makes a socket cookie be interpreted as a `struct sock *`, which is pointer confusion, but the demonstrated failure is an invalid dereference.
* Real lifetime or cleanup-state corruption: +1. Socket references are already dropped by the first `bpf_iter_tcp_put_batch()`, but the iterator state still makes the stop path process the batch again.
* Reliable kernel crash / strong DoS: +1. The report shows KASAN NULL pointer dereference followed by kernel panic.
* Hard or unreliable trigger condition: -1. The crash requires the `GFP_USER` realloc failure path after the batch was already converted to cookies.
* Requires privileged BPF access in typical deployments: -2. In many hardened/product configurations, BPF iterator creation is gated by CAP_BPF, CAP_SYS_ADMIN, CAP_NET_ADMIN, or root-controlled policy.

Paranoid additional signals:

* Local trigger with delegated BPF access: +1. If a local non-root or reduced-privilege service can access the BPF TCP iterator, the practical privilege level becomes PR:L rather than full host root.
* Weak LPE concern: +1. The cookie-as-`struct sock` interpretation is not a proven write primitive, but it is a kernel object confusion pattern in networking/BPF lifetime code.
* Local high-control kernel data-plane API: +1. Applies only in configurations where BPF iterator access is delegated or otherwise reachable without full host-root privileges.

Call-site confidence: high. The commit message and trace include the relevant path from `bpf_iter_tcp_batch()` to `bpf_iter_tcp_seq_stop()` and `bpf_iter_tcp_put_batch()`.

## 3. Reachability analysis

The bug is locally triggered through the BPF TCP iterator read path, not by incoming TCP packets. In typical secure deployments, unprivileged BPF is disabled, so creating or using the iterator usually requires elevated capabilities or a privileged service. Namespace and container setups matter: container root or reduced-capability service accounts with delegated BPF access should not be treated as full PR:H in practical risk terms. The path is not remotely network reachable, and reliable triggering also depends on hitting the realloc failure path.

## 4. Severity interpretation

This behaves above an ordinary local DoS because it is a BPF networking lifetime/state bug where released socket-pointer slots are later interpreted as live objects. However, the demonstrated primitive is still an invalid pointer dereference and kernel crash, not attacker-controlled reclaim, arbitrary write, callback control, or confirmed privilege escalation. Conservative handling is Low/ordinary Moderate for locked-down BPF deployments. Paranoid handling is Actionable Moderate because delegated BPF access plus object confusion in socket lifetime code deserves manual review.

## 5. One-sentence report phrase

A BPF TCP iterator realloc failure path can leave batch indexes pointing at cookie values instead of socket pointers, causing the stop path to treat cookies as `struct sock` objects and crash the kernel.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: although the proven impact is DoS, this is a BPF plus TCP socket lifetime bug with pointer confusion and double-release-like cleanup behavior, so it should not be auto-closed without checking product BPF exposure and whether delegated users can trigger the iterator path.

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

Patch: bpf: tcp: fix double sock release on batch realloc [ Upstream
Commit: 9f27c4f0ae35b5390ce4f7a54d3501144e41a54d
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9f27c4f0ae35b5390ce4f7a54d3501144e41a54d

Changed files:
  net/core/sock_diag.c
  net/ipv4/tcp_ipv4.c
  kernel/bpf/bpf_iter.c
  fs/read_write.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=9f27c4f0ae35b5390ce4f7a54d3501144e41a54d

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

The original Linux kernel CVE announcement for CVE-2026-64575 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64575

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:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 5.8

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: 2
  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: NO
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 alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).