[CVE-2026-98060][MODERATE 7.0] bpf: Reject resilient lock operations in rbtree callbacks [ Upstream

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

CVE: CVE-2026-98060
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: bpf: Reject resilient lock operations in rbtree callbacks [ Upstream
Commit: cc2e065ed206aecd9b94564779244f3ffb26e356
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=cc2e065ed206aecd9b94564779244f3ffb26e356
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98060
Analysis date: Fri, 25 Sep 2026 16:38:30 -0400
ActionableScore: 5
ActionableScore lower bound: unknown
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-98060 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98060

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.

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-98060	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98060 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:H/I:H/A:H';*CWE-416;CWE-362;CWE-667;CWE-703;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A race in the BPF rbtree path can occur because resilient lock operations were accepted inside a program supplied comparison callback even though __bpf_rbtree_add keeps parent and link pointers live across that callback. The callback can release the root lock and allow another CPU to remove and free the node referenced by the active tree walk. The walk can then resume with stale pointers and cause a use after free in kernel memory. For the CVSS the PR:L reflects a local user or delegated service that can load and execute an accepted BPF program. Some systems restrict this operation through CAP_BPF, CAP_SYS_ADMIN, or equivalent policy, but reduced capability or container based access should not automatically be treated as PR:H. AC:H is appropriate because successful triggering depends on concurrent activity and a race window. The issue is not directly network reachable. Impact is at least a local denial of service through kernel corruption or crash and may permit confidentiality and integrity impact or privilege escalation if the freed rbtree storage can be reused in a controlled way.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5)  SKIP CVE-2026-98060 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES  NO NO unknown 	MAYBE	BPF UAF HARDWARE LINUS  KPANIC INCREASED_TO_MODERATE7_FROM_MODERATE_BASED_ON_GUESSCVSS	-	-	checked

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

ActionableScore=5
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO

1. ActionableScore

* Raw conservative score: 5
* Conservative score: 5
* Raw paranoid score: 5
* Paranoid score: 5
* No floor or cap changed either score.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

2. Signal breakdown

Positive signals:

* +2 Real UAF and active lifetime violation. The comparison callback can release the rbtree root lock, another CPU can remove and free a node, and the interrupted tree walk subsequently resumes with parent and link pointers into the freed node.
* +1 Reliable kernel crash or strong DoS. Continuing an in-kernel rbtree traversal through freed pointers can realistically cause an invalid access, kernel fault, or structural tree corruption.
* +1 Attacker-influenced active-object lifetime. The accepted BPF program controls the callback that releases the required lock and can arrange concurrent operations that remove the node while the tree walk remains active.
* +1 Structured stale-object exploitation leverage. The stale values are active rbtree parent and link pointers consumed by an ongoing insertion or traversal, rather than a shallow cleanup-only dereference. Their use influences pointer traversal and tree mutation after the node lifetime has ended.

Negative signals:

* No privilege penalty. The complete BPF loading and execution privilege boundary is unresolved. Host-admin-equivalent privilege cannot be assumed.
* No race penalty. The commit establishes a concurrency window but does not show that it is narrow, one-shot, or externally uncontrollable. BPF operations can potentially coordinate and repeat both sides.
* No niche-subsystem penalty. BPF privilege gating affects reachability, but specialization alone is not evidence for a negative point.

Important non-awarded signals:

* Controlled reclaim or attacker-shaped replacement of the freed node is not demonstrated.
* Arbitrary or directed kernel read/write is not demonstrated.
* Strong LPE leverage +2 is not awarded merely because this is a BPF UAF.
* Confidentiality and integrity points are not awarded because no disclosure, controlled replacement, or directed corruption consequence is established.
* No extra Availability point is awarded for the same possible crash.
* Remote reachability is not established.
* No concrete repeated release or refcount operation on the same dangling reference exists. The issue instead involves stale rbtree traversal pointers.
* No additional paranoid point is awarded because stronger exploitation would require an unproven reclaim or replacement primitive.
* The BPF privileged-control-plane cap was checked. It does not alter the score of 5, and the cleanup-only exception does not apply because the stale pointers are used during an active tree operation.

3. Reachability analysis

The trigger requires loading and executing a BPF program that uses resilient locks to protect a BPF rbtree and invokes resilient lock or unlock kfuncs from its comparison callback. The program must also cause a concurrent operation to remove and free the node referenced by the interrupted tree walk.

The supplied evidence does not establish whether the complete sequence is available to an ordinary user, a delegated CAP_BPF service, container root, or only a host administrator. Current products commonly restrict BPF loading through CAP_BPF, CAP_SYS_ADMIN, related capabilities, and the unprivileged BPF sysctl, but those deployment assumptions are insufficient to prove HostAdminRequired=YES.

No attachment or netdevice operation is shown, and the evidence does not establish that all required BPF operations are available in an attacker-created namespace. NamespaceScopedPrivilege therefore remains UNKNOWN. Prior host configuration may be required on products with unprivileged BPF disabled, but the exact prerequisite is unresolved.

No special hardware or network exposure is required. The race appears repeatable because the program can release the lock from the callback while concurrent BPF activity removes nodes. The evidence does not prove a materially narrow or uncontrollable timing window.

4. Primitive and severity interpretation

The exact primitive is an active structured-object UAF. `__bpf_rbtree_add()` retains parent and link pointers while invoking a program-supplied comparator. The comparator can improperly release the resilient lock, allowing another CPU to remove and free the referenced node. The original walk then resumes and consumes pointers associated with the freed node.

This is broader than an ordinary stale cleanup dereference. It occurs during an active rbtree traversal or insertion, and the stale state affects pointer traversal and potentially tree linkage. It is therefore CLASS_B rather than crash-only CLASS_C.

There is no concrete repeated release or refcount mutation. The first lifetime-ending operation is the concurrent removal and free, while the later operation is traversal through stale parent and link pointers rather than another put or free.

The demonstrated consequence is kernel use-after-free with plausible crash or rbtree corruption. A controlled replacement object, arbitrary read/write, information disclosure, or privilege escalation is not demonstrated. Exploitation beyond crash remains plausible enough to require analysis because active pointer traversal continues after free, but it is not sufficiently controlled to qualify as CLASS_A.

ImportantCandidate=YES because this is a strong unresolved active-object UAF with attacker-influenced lock and lifetime behavior. AutoDowngradeAllowed=NO because automatically treating it as an ordinary DoS could discard meaningful unresolved exploitation leverage in the stale tree traversal. The practical classification is Actionable Moderate at minimum, with Important classification dependent on BPF privilege reachability and whether controlled reclaim or a useful post-free write can be established.

5. One-sentence report phrase

A BPF rbtree comparison callback can release a resilient root lock and permit concurrent node removal, after which the active tree walk resumes with freed parent and link pointers and creates a kernel use-after-free requiring manual exploitation review.

6. Manual review recommendation

MANUAL CHECK REQUIRED

The patch establishes an active rbtree UAF with attacker-influenced lifetime behavior, while the BPF privilege boundary and exploitation value of the stale parent and link pointers remain unresolved.

7. Call-site confidence

Call-site confidence: medium

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

Patch: bpf: Reject resilient lock operations in rbtree callbacks [ Upstream
Commit: cc2e065ed206aecd9b94564779244f3ffb26e356
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=cc2e065ed206aecd9b94564779244f3ffb26e356

Changed files:
  kernel/bpf/verifier.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=cc2e065ed206aecd9b94564779244f3ffb26e356

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

The original Linux kernel CVE announcement for CVE-2026-98060 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98060

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: 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).