[CVE-2026-64508][MODERATE 7.0] bpf: Support for hardening against JIT spraying

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

CVE: CVE-2026-64508
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: bpf: Support for hardening against JIT spraying
Commit: 6e52c240c43a601b681e3a4e58fc5685114d4726
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6e52c240c43a601b681e3a4e58fc5685114d4726
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64508
Analysis date: Sat, 25 Jul 2026 05:57:38 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: NO

Summary:
BPF JIT pack memory reuse could preserve indirect branch predictor state from a previous program, allowing a local user with access to small cBPF or BPF program loading to attempt JIT spraying style speculative execution attacks with plausible confidentiality impact.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-64508 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64508

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: NO

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-2026-64508	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:L/A:N';CWE-1420;CWE-693;CWE-203;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:N';BEST CVSS score: '5.3';DESCR 'BPF JIT pack reuse can leave indirect branch predictor state from an older program at the same executable memory location. A local attacker able to load small cBPF or BPF programs may try to shape old and new JIT code so that an indirect jump into the new program reuses stale predictions, which is a JIT spraying and transient execution hardening concern. For the CVSS the PR:L is used because reliable triggering requires local code execution or a local process that can create the relevant BPF programs, not just remote packet delivery. The issue is not directly network reachable. Impact is primarily potential confidentiality exposure or mitigation bypass through speculative execution, with no direct kernel crash or conventional memory corruption primitive shown by the patch context.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 5)	YES	INIT BPF HARDWARE TEST KPANIC MEMORY 	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 5
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

* Local unprivileged trigger: +1
  The commit explicitly mentions cBPF as the unprivileged attack surface, and small programs are the relevant JIT pack reuse case.

* Local high-control BPF/JIT shaping surface: +1
  An attacker who can load many small cBPF or BPF programs may influence old and new JIT code placement within reused executable pack memory.

* Confidentiality impact plausible: +1
  The issue is a speculative execution and JIT spraying hardening concern. The realistic impact is potential leakage or mitigation bypass, not direct memory corruption.

* Broad/default/common subsystem exposure: +1
  BPF JIT is a widely deployed kernel subsystem, although actual reachability depends on BPF JIT enablement and local BPF privilege policy.

* Paranoid manual-review uplift: +1
  BPF JIT hardening against branch predictor reuse is historically security-sensitive. The patch does not show conventional memory corruption, but the class is subtle enough to avoid auto-close.

Not counted:

* No generic memory corruption bonus. The patch does not show UAF, OOB write, double free, refcount abuse, type confusion, or arbitrary write.
* No reliable kernel crash bonus. The described risk is branch predictor state reuse, not an Oops or panic.
* No remote reachable bonus. The issue requires local ability to create relevant BPF/cBPF programs.
* No privilege escalation bonus. LPE is not demonstrated by the patch context.

## 3. Reachability analysis

The likely attacker is a local user or local process that can create small cBPF or BPF programs and cause reuse of BPF JIT pack memory. The path is not directly network reachable. Remote packets alone are insufficient unless there is a separate local component that installs attacker-shaped filters.

Namespace and product policy matter. If unprivileged BPF and relevant cBPF JIT paths are disabled or require CAP_BPF, CAP_SYS_ADMIN, CAP_NET_ADMIN, or root-controlled sysctls, reachability drops and the conservative score should be closer to 2 or 3. If cBPF remains available to unprivileged users, the score of 4 to 5 is defensible.

Realistic exploitation requires shaping JIT code placement and branch predictor state. That is substantially harder than triggering a normal memory safety bug, but it is still security-relevant because it targets speculative execution behavior in executable kernel memory.

## 4. Severity interpretation

This behaves more like an actionable Moderate than an ordinary Moderate. It is not an Important memory corruption bug by itself, because there is no concrete UAF, overwrite, type confusion, or reclaim primitive in the patch.

The theoretical risk is confidentiality exposure or mitigation bypass via branch predictor state reuse. The realistic evidence supports manual review because BPF JIT hardening patches may hide architecture-specific exploitation details, but not automatic escalation to Important without additional exploit evidence.

## 5. One-sentence report phrase

BPF JIT pack memory reuse could preserve indirect branch predictor state from a previous program, allowing a local user with access to small cBPF or BPF program loading to attempt JIT spraying style speculative execution attacks with plausible confidentiality impact.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: this is not conventional memory corruption, but it affects BPF JIT executable memory reuse and speculative execution hardening. It should not be auto-closed without checking the target product policy for cBPF/BPF availability, BPF JIT defaults, and architecture-specific predictor flush support.

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

Patch: bpf: Support for hardening against JIT spraying
Commit: 6e52c240c43a601b681e3a4e58fc5685114d4726
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6e52c240c43a601b681e3a4e58fc5685114d4726

Commit description:

The BPF JIT allocator packs many small programs into larger executable
allocations and reuses space within those allocations as programs are
loaded and freed. When fresh code is written into space that a previous
program occupied, an indirect jump into the new program can reuse a branch
prediction left behind by the old one.

Flush the indirect branch predictors before reusing JIT memory so that
indirect jumps into a newly written program don't reuse predictions from an
old program that occupied the same space.

Introduce bpf_arch_pred_flush_enabled static key and bpf_arch_pred_flush
static call for flushing the branch predictors on JIT memory reuse.
Architectures that need a flush, can update it to a predictor flush
function. By default, its a NOP and does not emit any CALL.

Allocations larger than a pack are not covered by this flush. That is safe
because cBPF programs (the unprivileged attack surface) are bounded well
below a pack size. Issue a warning if this assumption is ever violated
while the flush is active.

Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>

Changed files:
  include/linux/filter.h
  crypto/sha1.h
  net/sch_generic.h
  kernel/bpf/core.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=6e52c240c43a601b681e3a4e58fc5685114d4726

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

The original Linux kernel CVE announcement for CVE-2026-64508 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64508

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:N
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:L/A:N
  The Best / paranoid CVSS score: 5.3

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: 4
  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 alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).