* [CVE-2026-93125][IMPORTANT] bpf: Reject rdonly/rdwr_buf_size kfunc arguments that exceed u32 max [ Upstream
@ 2026-09-17 22:23 21% AL-KERNEL
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From: AL-KERNEL @ 2026-09-17 22:23 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-93125
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: bpf: Reject rdonly/rdwr_buf_size kfunc arguments that exceed u32 max [ Upstream
Commit: 56a3846830ac95a472297d0cbba75cbff29540bb
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=56a3846830ac95a472297d0cbba75cbff29540bb
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93125
Analysis date: Thu, 17 Sep 2026 18:23:50 -0400
ActionableScore: 7
ActionableScore lower bound: 5
Actionable bucket: Strong Important candidate
Manual review required: YES
Summary:
A BPF verifier integer truncation bug can let oversized rdonly_buf_size or rdwr_buf_size kfunc arguments produce an incorrect PTR_TO_MEM bound, potentially allowing local BPF code with load capability to perform out-of-bounds kernel memory access and requiring manual review for DoS or privilege escalation impact.
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ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-93125 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93125
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.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2026-93125 IMPORTANT https://www.kernelcve.org/list/?q=CVE-2026-93125 CHECK WITH IMPACT FROM ORIG NN LOW Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H';CWE-681;CWE-190;*CWE-787;BEST CVSS score: '7.8';DESCR 'A BPF verifier bounds bug can occur when a kfunc argument named rdonly_buf_size or rdwr_buf_size is larger than U32_MAX. The verifier stores the value in a u64 field and later copies it into a u32 mem_size field for the returned PTR_TO_MEM register, which can truncate the value and leave the verifier with an incorrect memory bound. A local attacker able to load a BPF program that reaches this kfunc path may use the wrong bound for out of bounds access to kfunc returned memory. For the CVSS the PR:L is used because exploitation requires a local process with BPF program load capability, but this can be delegated by CAP_BPF or similar policy and is not equivalent to full root in all deployments. The issue is not network reachable. Impact may include kernel memory corruption, denial of service, and potential privilege escalation.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate (with actual score 6) YES BPF SIMPLEFIX IMPROVEONLY LINUS KPANIC INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHERTHAN5 YES NO checked
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ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=7
ActionableScoreLower=5
PrimitiveClass=CLASS_A
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
## 1. ActionableScore
* Raw conservative score: 5
* Conservative score: 5. No floor or cap changed the score.
* Raw paranoid score: 7
* Paranoid score: 7. No floor or cap changed the score.
* Final recommended bucket: **Strong Important candidate**::
## 2. Signal breakdown
Conservative signals:
* +2: Strong corruption primitive. The BPF verifier can accept a kfunc buffer size above U32_MAX, store it as u64, then truncate it into a u32 `mem_size`, causing later verifier bounds checks to use an incorrect bound for a returned `PTR_TO_MEM`.
* +1: Confidentiality plausible. The `rdonly_buf_size` path can plausibly allow out-of-bounds reads from kfunc-returned kernel memory, and BPF programs commonly have ways to copy observed values to maps or user-visible outputs.
* +1: Integrity plausible. The `rdwr_buf_size` path plausibly allows out-of-bounds writes relative to the returned memory object.
* +1: Reliable kernel crash / DoS plausible. Invalid verifier-approved memory access can realistically fault or corrupt kernel memory.
Paranoid additional signal:
* +2: Strong LPE plausibility / strong exploitation leverage. The issue is not merely a validation warning. It is a verifier bounds bypass that may permit attacker-selected BPF memory operations outside the real allocation, especially through the `rdwr` path.
Non-awarded / not double-counted signals:
* RealUAF not awarded. This is not a lifetime or stale-object bug.
* Concrete repeated release/refcount not awarded. No first release, surviving dangling reference, or second lifetime mutation is present.
* Remote reachability not awarded. The path is local BPF program loading, not network packet handling.
* Local unprivileged trigger not awarded. Ordinary unprivileged reachability is not established.
* NamespaceScopedPrivilege=UNKNOWN. The full load/kfunc/attach/execute chain is not proven namespace-scoped.
* Extra availability not awarded. The crash/corruption availability effect is already counted once.
* No arbitrary read/write is claimed as demonstrated. The established primitive is verifier-approved OOB access, not a proven fully arbitrary kernel R/W primitive.
## 3. Reachability analysis
The vulnerable path is reached through BPF verifier handling of kfunc arguments named `rdonly_buf_size` or `rdwr_buf_size`. An attacker must be able to load a BPF program that reaches the affected kfunc path and supplies a constant size value above U32_MAX.
The complete privilege boundary is not fully resolved from the supplied patch alone. In modern deployments, BPF loading is often gated by CAP_BPF, CAP_SYS_ADMIN, CAP_NET_ADMIN, LSM policy, sysctls, or product-specific delegation. This does not prove host-admin-equivalent privilege is required, but it also does not prove ordinary unprivileged reachability. Therefore HostAdminRequired=UNKNOWN and NamespaceScopedPrivilege=UNKNOWN.
No direct network trigger is established. No special hardware dependency is apparent. This is not a race and no timing penalty applies.
## 4. Primitive and severity interpretation
The exact primitive is an integer truncation / bounds validation flaw in the BPF verifier. A u64 kfunc buffer size can exceed U32_MAX, then be copied into a u32 `mem_size`, causing the verifier to track an incorrect memory size for the returned `PTR_TO_MEM`.
This is an active verifier memory-safety bug, not a cleanup-only issue and not a resource leak. The strongest patch-supported consequence is out-of-bounds access to kfunc-returned memory from a loaded BPF program. The `rdwr` case makes integrity impact and potential kernel memory corruption plausible.
PrimitiveClass=CLASS_A because an attacker-influenced verifier bounds bypass with plausible OOB write is a strong kernel corruption primitive. RealUAF=NO because no post-lifetime object use is established.
ImportantCandidate=YES because BPF verifier memory-safety bugs with plausible OOB write require Important-vs-Moderate manual review even without a complete exploit chain. AutoDowngradeAllowed=NO because automatic closure would discard a concrete kernel corruption primitive.
## 5. One-sentence report phrase
A BPF verifier integer truncation bug can let oversized rdonly_buf_size or rdwr_buf_size kfunc arguments produce an incorrect PTR_TO_MEM bound, potentially allowing local BPF code with load capability to perform out-of-bounds kernel memory access and requiring manual review for DoS or privilege escalation impact.
## 6. Manual review recommendation
MANUAL CHECK REQUIRED
The patch establishes a concrete BPF verifier bounds bypass with plausible out-of-bounds read/write impact, and the exact product privilege model and reachable kfunc surface must be reviewed.
## 7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: bpf: Reject rdonly/rdwr_buf_size kfunc arguments that exceed u32 max [ Upstream
Commit: 56a3846830ac95a472297d0cbba75cbff29540bb
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=56a3846830ac95a472297d0cbba75cbff29540bb
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=56a3846830ac95a472297d0cbba75cbff29540bb
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-93125 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93125
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: Not available
The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
The Best / paranoid CVSS score: 7.8
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: 5
Paranoid ActionableScore: 7
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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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