[CVE-2026-98799][IMPORTANT] bpf: Skip detached progs in trampoline images that are still in use [ Upstream

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

CVE: CVE-2026-98799
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: bpf: Skip detached progs in trampoline images that are still in use [ Upstream
Commit: 967566ad325b42150483e81acb09ea9d800c00b8
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=967566ad325b42150483e81acb09ea9d800c00b8
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98799
Analysis date: Sat, 24 Oct 2026 11:04:43 -0400
ActionableScore: 5
ActionableScore lower bound: unknown
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
A BPF trampoline detach race can free a program while an old live trampoline still calls its JIT image, causing control flow into freed executable memory and a demonstrated kernel Oops.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-98799 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98799

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: IMPORTANT
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-2026-98799	IMPORTANT	https://www.kernelcve.org/list/?q=CVE-2026-98799 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT IMPORTANT AEGIS_AS=6 LEGACY=IMPORTANT RESULT=SAME INDEPENDENT_LEGACY=MODERATE_KPANIC INDEPENDENT_RESULT=DIFF TEMP_KPANIC_MERGE=IMPORTANT_HARD_VETO PRE_MERGE_LEGACY=MODERATE_KPANIC (final reconciliation agrees; DECISION: both IMPORTANT)	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-362;*CWE-672;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A lifetime race in BPF trampolines allows a detached program to be freed while a task sleeping in an earlier sleepable program can still resume in an old trampoline image and call the detached program through its stale bpf_func state. This is a concrete use after free with control flow entering freed JIT program memory, and the observed x86 result is an int3 kernel Oops from poisoned bpf_prog_pack memory. For the CVSS the PR:L value reflects that reliable triggering requires permission to attach and detach tracing BPF programs, but this can be delegated through capabilities or a privileged service and does not necessarily require unrestricted root control. AC:H reflects the required timing between a sleeping trampoline invocation, program detach, grace periods, and resumed execution. The demonstrated impact is a local kernel crash, while reuse of freed executable memory makes confidentiality and integrity impact plausible enough for a paranoid HHH manual review. The issue is not directly network reachable. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 7 and the production ActionableScore returned 5 with recommendation Actionable Moderate / Strong Important candidate requiring manual review. 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. final reconciliation stage MODERATE_KPANIC to IMPORTANT because a specific evidence based protection or manual review veto was applied. 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 TEMP_KPANIC_MERGE_IMPORTANT_VETO. The independent weaker Aegis shadow evaluated CVSS unavailable and ActionableScore 6 with primitive class CLASS_B and manual review REQUIRED. Its independently reconciled impact was IMPORTANT. Cross model aggregation changed the production result under an enabled evidence gated merge rule. The final reported impact is IMPORTANT.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5)	MAYBE	OOB LOCK INIT BPF UAF LOG HARDWARE LINUS  KPANIC INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK TEMP_KPANIC_MERGE_IMPORTANT_VETO	-	-	checked

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

ActionableScore=5
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw base score: 4.
* Conservative score: 5. REAL UAF FLOOR 5 applies because the attacker-controlled detach transition leaves an old trampoline actively executing and later transfers control into the freed program’s JIT image.
* Raw paranoid score: 4.
* Paranoid score: 5. No additional speculative reclaim or LPE point is awarded.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

2. Signal breakdown

* +2 Real UAF: detaching `P` drops its last reference; after grace periods it is freed, while a task sleeping in preceding program `S` can resume and invoke `P`.
* +1 Reliable kernel crash: x86 execution entered poisoned `bpf_prog_pack` memory and produced an `int3` Oops.
* +1 Attacker-influenced lifetime transition: an actor able to install sleepable trampoline programs and detach `P` can drive the invocation/detachment sequence that creates the stale call.
* Floor 5: this is not cleanup-only use. The stale trampoline performs active control transfer to freed executable JIT storage.

Not awarded:

* No controlled reclaim, attacker-shaped post-free replacement, arbitrary write, disclosure, or LPE is shown.
* No separate structured-leverage point: execution of the stale fixed call target is already central to the UAF; useful replacement of that target is unproven.
* No race penalty: timing is required, but production and fuzzer reproduction contradict a proven narrow or one-shot race.
* No extra availability point beyond the same Oops.
* B4-PENDING is inapplicable because no authorization decision changes from DENY to ALLOW.

3. Reachability analysis

The complete trigger requires BPF trampoline program loading/attachment, a sleepable program invocation, detachment of a later program, completion of grace periods, and resumption of the sleeping task. The actor controlling attach/detach can materially drive the lifetime transition, but the supplied evidence does not establish whether all operations are available to an ordinary user, delegated capability holder, privileged service, or only a host administrator. It also does not establish a fully namespace-scoped path. No remote reachability or special hardware requirement exists. Prior BPF policy/sysctl and capability requirements remain unresolved.

4. Primitive and severity reading

This is an active-program lifetime violation, not fixed stale I/O storage: a trampoline image remains executable after its referenced `bpf_prog` and JIT code can be freed, then directly calls the stale address. The proven consequence is host-kernel control flow into poisoned freed executable memory and an Oops. Useful reclaim or attacker-directed replacement is unproven, so this remains CLASS_B rather than CLASS_A.

ImportantCandidate is YES because active kernel execution reaches post-lifetime executable state and exploit leverage beyond the demonstrated crash remains materially unresolved. AutoDowngradeAllowed is NO because reducing it to an ordinary privileged crash would discard that concrete active-state UAF primitive.

5. One-sentence report phrase

A BPF trampoline detach race can free a program while an old live trampoline still calls its JIT image, causing control flow into freed executable memory and a demonstrated kernel Oops.

6. Manual review advice

MANUAL CHECK REQUIRED

Review BPF privilege boundaries and whether JIT-pack reuse can turn the stale executable call into controlled post-free execution.

7. Call-site confidence

Call-site confidence: high

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

Patch: bpf: Skip detached progs in trampoline images that are still in use [ Upstream
Commit: 967566ad325b42150483e81acb09ea9d800c00b8
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=967566ad325b42150483e81acb09ea9d800c00b8

Changed files:
  arch/arm64/net/bpf_jit_comp.c
  arch/loongarch/net/bpf_jit.c
  arch/powerpc/net/bpf_jit_comp.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=967566ad325b42150483e81acb09ea9d800c00b8

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

The original Linux kernel CVE announcement for CVE-2026-98799 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98799

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: unknown
  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: IMPORTANT
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): IMPORTANT

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).