* [CVE-2026-93173][LOW] bpf,lsm: Drop bpf_prog_free from sleepable_lsm_hooks [ Upstream
@ 2026-09-18 0:04 21% AL-KERNEL
0 siblings, 0 replies; 1+ results
From: AL-KERNEL @ 2026-09-18 0:04 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-93173
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: bpf,lsm: Drop bpf_prog_free from sleepable_lsm_hooks [ Upstream
Commit: 2135f661fae7160a7fc603cab43cbc7999e8bfce
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2135f661fae7160a7fc603cab43cbc7999e8bfce
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93173
Analysis date: Thu, 17 Sep 2026 20:04:07 -0400
ActionableScore: 2
ActionableScore lower bound: 1
Actionable bucket: Ordinary Moderate
Manual review required: NO
Summary:
No one-sentence report phrase was found.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-93173 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93173
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: LOW
Manual review required: NO
A detailed explanation of the methodology and priority rules is included
at the end of this message.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2026-93173 LOW https://www.kernelcve.org/list/?q=CVE-2026-93173 CHECK WITH IMPACT FROM ORIG NN MODERATE Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';CWE-667;CWE-703;CWE-755;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.5';DESCR 'A sleepable BPF LSM program could be attached to the bpf_prog_free hook even though security_bpf_prog_free can run from the __bpf_prog_put_rcu RCU callback in softirq context. When that sleepable observer runs from atomic context, __bpf_prog_enter_sleepable can hit might_fault and trigger a sleeping function BUG. For the CVSS the PR:L is used in the paranoid score because some deployments delegate BPF related capabilities to service accounts, container root, or reduced capability root even though the typical base case is administrator controlled. The issue is not network reachable and requires local ability to load and attach the relevant BPF LSM program. Impact is denial of service through a warning or kernel crash depending on kernel panic policy. No concrete UAF, OOB access, arbitrary write, or information leak primitive is indicated by the patch context.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2) YES INIT BPF UAF LINUS DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 YES NO checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=2
ActionableScoreLower=1
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES
1. ActionableScore
* Raw conservative score: 1
* Conservative score: 1
* Raw paranoid score: 2
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate**::
No floor or cap changed the score.
2. Signal breakdown
Conservative signals:
* +1: Demonstrated invalid execution context. A sleepable BPF LSM observer can run from an RCU softirq callback and trigger `BUG: sleeping function called from invalid context`.
* +0: No proven ordinary unprivileged trigger. Loading and attaching BPF LSM programs is privilege gated.
* +0: No Real UAF. The RCU callback context is involved, but the patch does not establish post-lifetime use of `struct bpf_prog` or another object.
* +0: No concrete repeated release or refcount mutation on the same dangling reference.
* +0: No controlled reclaim, arbitrary write, OOB access, information leak, callback hijack, or security-boundary bypass.
* +0: Extra availability not awarded. The same BUG/WARN symptom is the only demonstrated availability effect.
Paranoid signals:
* +1: Same invalid-context BUG signal as conservative.
* +1: In deployments with `panic_on_warn` or equivalent fatal warning policy, the BUG/WARN can become a kernel crash or host DoS.
Negative signals:
* No -2 host-admin penalty applied because the exact complete privilege boundary is not fully established from the supplied input.
* No race penalty applied. This is mainly a context mismatch between sleepable hooks and softirq execution, not a narrow timing race.
* No niche subsystem penalty applied. BPF privilege gating affects reachability, but the subsystem being BPF is not itself a reducing signal.
3. Reachability analysis
The trigger requires local ability to load and attach a sleepable BPF LSM program to `bpf_prog_free`, and then cause a non-sleepable BPF program to be freed through `__bpf_prog_put_rcu()`. The vulnerable callback path runs in softirq context via RCU.
Ordinary unprivileged reachability is not established. BPF LSM program loading and attachment are normally controlled by BPF-related capabilities and system policy. The supplied evidence does not prove whether the complete trigger requires host-admin-equivalent privilege or can be performed by a delegated service account, container root, or reduced-capability process. Therefore `HostAdminRequired=UNKNOWN`.
No complete namespace-scoped trigger is established. The patch does not show that all BPF load, attach, trigger, and cleanup stages can be performed inside attacker-created namespaces. Therefore `NamespaceScopedPrivilege=UNKNOWN`.
No network reachability is established. This is a local BPF/LSM control-plane issue, not packet-triggered behavior. No special hardware requirement is present.
4. Primitive and severity interpretation
The primitive is an invalid-context execution bug: a sleepable BPF LSM hook can be invoked from an RCU softirq callback where sleeping or faulting is not allowed. This results in a `might_fault()` / sleeping-function BUG.
This is not a real UAF. The commit explicitly discusses RCU callback context and the lifetime of `prog->aux->security`, but the actual fixed issue is that sleepable observers were allowed on a hook that may execute from non-sleepable softirq context. The patch removes `bpf_lsm_bpf_prog_free` from `sleepable_lsm_hooks`.
Primitive class is `CLASS_C`: demonstrated behavior is primarily BUG/WARN/DoS without an independently useful corruption or lifetime primitive.
Demonstrated consequence: local denial of service or warning, depending on kernel panic policy.
Speculative consequence: broader memory corruption or privilege escalation is not supported by the patch context.
ImportantCandidate is `NO` because there is no Class A primitive, no Real UAF, no repeated lifetime mutation, no controlled reclaim, and no security-boundary bypass.
AutoDowngradeAllowed is `YES` because the established issue is a privilege-gated local invalid-context BUG with no unresolved Important-grade exploitation primitive.
Likely operational severity: ordinary Moderate / Low-like kernel DoS, mainly relevant to systems permitting privileged or delegated BPF LSM program management.
5. One-sentence report phrase
A sleepable BPF LSM program could be attached to `bpf_prog_free` even though that hook may run from an RCU softirq callback, causing a sleeping-function BUG and possible local DoS when BPF LSM programs can be loaded and attached.
6. Manual review recommendation
NO MANUAL CHECK NEEDED
Reason: no UAF, no memory corruption primitive, no authorization bypass, no network reachability, and no evidence of exploitation beyond local BUG/WARN or panic-policy-dependent DoS.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: bpf,lsm: Drop bpf_prog_free from sleepable_lsm_hooks [ Upstream
Commit: 2135f661fae7160a7fc603cab43cbc7999e8bfce
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2135f661fae7160a7fc603cab43cbc7999e8bfce
Changed files:
kernel/bpf/trampoline.c
security/security.c
kernel/bpf/syscall.c
kernel/rcu/tree.c
kernel/softirq.c
kernel/bpf/bpf_lsm.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=2135f661fae7160a7fc603cab43cbc7999e8bfce
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-93173 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93173
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:L/PR:H/UI:N/S:U/C:N/I:N/A:L
The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
The Best / paranoid CVSS score: 5.5
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: 1
Paranoid ActionableScore: 2
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: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW
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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