[CVE-2026-72110][MODERATE 7.0] bpf,fork: wipe ->bpf_storage before bailouts that access it

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

CVE: CVE-2026-72110
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: bpf,fork: wipe ->bpf_storage before bailouts that access it
Commit: c3fd6f28c7ce1142a3b23dbb840eaa4777de1d74
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c3fd6f28c7ce1142a3b23dbb840eaa4777de1d74
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72110
Analysis date: Sun, 16 Aug 2026 04:37:28 -0400
ActionableScore: 6
ActionableScore lower bound: 4
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A BPF task local storage lifetime bug in fork can leave a copied parent bpf_storage pointer in a partially created child task, allowing an early copy_process bailout to free or corrupt storage it does not own and causing at least local DoS with possible UAF based privilege escalation concern.

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

The original Linux kernel CVE announcement for CVE-2026-72110 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72110

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-2026-72110	MODERATE	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-665;CWE-824;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A use-after-free risk exists in the BPF task local storage fork path because dup_task_struct copies the parent task bpf_storage pointer into the new task before copy_process can fail and free the new task. If an early bailout such as RLIMIT_NPROC failure happens before bpf_storage is reset, free_task can treat the copied pointer as owned by the child and pass it to bpf_task_storage_free and bpf_local_storage_destroy, which can corrupt or free storage that belongs to another task. For the CVSS the PR:L is used because a local process can trigger fork failure paths once it is associated with BPF task storage, although creating or attaching that storage may depend on system BPF policy or privileged tracing infrastructure. The issue is not network reachable. Impact is at least local denial of service via kernel hang or crash, and because the patch context explicitly mentions UAF, worst case impact may include privilege escalation and should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 5)	YES	INIT BPF UAF HARDWARE LINUS  INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=6
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 6
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Generic memory corruption, strong primitive: +2. The commit explicitly states UAF and the copied child task can carry a stale parent `bpf_storage` pointer into `free_task()`.
* Real lifetime corruption: +1. This is a task lifetime initialization bug where cleanup can operate on storage not owned by the nascent task.
* Reliable kernel crash / strong DoS: +1. The commit explicitly mentions kernel hangs and UAF.
* Broad/default/common subsystem interaction: +1. The affected path is `fork()` / `copy_process()`, but the vulnerable state requires BPF task local storage.
* Requires admin/root/CAP_* in typical deployments: -2. Creating or attaching BPF task storage is commonly gated by CAP_BPF, CAP_SYS_ADMIN, tracing privileges, or root controlled BPF policy.

Paranoid additional signals:

* Local unprivileged trigger: +1. Once a process has been inserted into a task storage map, the actual failure path can be driven by local fork activity and RLIMIT_NPROC exhaustion.
* Weak LPE concern: +1. The bug is a real UAF/lifetime corruption issue, but no attacker controlled reclaim, overwrite, callback control, or type confusion primitive is demonstrated.
* Confidentiality impact plausible: +1. Only for paranoid handling, because UAF in task local storage may expose stale object lifetime effects.
* Integrity impact plausible: +1. Only for paranoid handling, because freeing or corrupting another task storage object may affect kernel state.
* BPF gating cap applies. Because BPF task storage setup is typically privileged and no working LPE or controlled reclaim is shown, paranoid ActionableScore is capped at 6.

## 3. Reachability analysis

The vulnerable cleanup path is local, not network reachable. A process must have BPF task local storage associated with it, and then `copy_process()` must fail before `bpf_storage` is reinitialized, such as through an RLIMIT_NPROC failure path. In typical hardened distributions, unprivileged BPF is disabled and creating or attaching the relevant BPF storage requires elevated privileges. However, if a privileged tracing or observability component attaches task storage to ordinary user processes, an unprivileged local process may be able to trigger the fork bailout path afterward.

Namespaces and containers matter mostly through BPF policy. Container root without host BPF privileges is usually not enough to create the condition, but a host tracing setup or delegated BPF capability could make the trigger reachable from reduced privilege contexts.

Call-site confidence: high. The commit message gives the exact call chain from `copy_process()` to `free_task()` and `bpf_task_storage_free()`.

## 4. Severity interpretation

This is not an ordinary low-risk cleanup bug. It is a real lifetime bug with explicit UAF and kernel hang impact in a core process creation path. Realistic exploitation evidence supports local DoS more strongly than privilege escalation. LPE remains a paranoid concern because the stale pointer is a kernel object lifetime violation, but the patch does not show controlled reclaim, arbitrary write, callback hijack, or object replacement.

Overall this should be treated as Actionable Moderate at minimum, with Important-candidate manual review because the bug class is UAF in task/BPF storage lifetime handling.

## 5. One-sentence report phrase

A BPF task local storage lifetime bug in fork can leave a copied parent bpf_storage pointer in a partially created child task, allowing an early copy_process bailout to free or corrupt storage it does not own and causing at least local DoS with possible UAF based privilege escalation concern.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: the patch explicitly fixes a UAF-capable lifetime bug in `fork()` cleanup involving BPF task local storage. Even though BPF privilege gating limits default exposure, the UAF and reduced privilege trigger scenarios are important enough to avoid auto-closing.

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

Patch: bpf,fork: wipe ->bpf_storage before bailouts that access it
Commit: c3fd6f28c7ce1142a3b23dbb840eaa4777de1d74
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c3fd6f28c7ce1142a3b23dbb840eaa4777de1d74

Commit description:

Currently, copy_process() can bail out to free_task() before p->bpf_storage
has been initialized, with this call graph (shown here for the
!CONFIG_MEMCG case):

copy_process
  dup_task_struct
    arch_dup_task_struct
      [copies the entire task_struct, including ->bpf_storage member]
  [RLIMIT_NPROC check fails]
  delayed_free_task
    free_task
      bpf_task_storage_free
        rcu_dereference(task->bpf_storage)
        bpf_local_storage_destroy

In this case, the nascent task's ->bpf_storage member that
bpf_local_storage_destroy() operates on is a plain copy of the parent's
->bpf_storage pointer, not a real initialized pointer.
This leads to badness (kernel hangs, UAF).

This is reachable as long as the process calling fork() has been inserted
into a task storage map.

Cc: stable@kernel.org
Fixes: a10787e ("bpf: Enable task local storage for tracing programs")
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  kernel/fork.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=c3fd6f28c7ce1142a3b23dbb840eaa4777de1d74

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

The original Linux kernel CVE announcement for CVE-2026-72110 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72110

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:L/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7

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: 4
  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: 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).