[CVE-2026-99129][MODERATE 7.0] selinux: fix BPF token permission checks

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

CVE: CVE-2026-99129
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: selinux: fix BPF token permission checks
Commit: e1ef306ba20eb13099ca4463527890df67619405
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e1ef306ba20eb13099ca4463527890df67619405
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99129
Analysis date: Wed, 28 Oct 2026 22:08:50 -0400
ActionableScore: 5
ActionableScore lower bound: unknown
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
A shared-fd-table race can make SELinux authorize BPF map creation or program loading against an unrelated bpffs creator SID while BPF core uses the original token.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-99129 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99129

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.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-99129	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-99129 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=1 LEGACY=MODERATE_KPANIC RESULT=SAME (final reconciliation agrees; DECISION: both MODERATE_KPANIC)	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:H/A:L';CWE-367;CWE-362;CWE-863;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:L';BEST CVSS score: '5.8';DESCR 'SELinux BPF token permission checks could use a creator SID obtained by looking up the numeric token file descriptor again after BPF core had already resolved the real token or path. A second local thread sharing the file table could replace that descriptor during the race window, causing SELinux to authorize MAP_CREATE or PROG_LOAD against an unrelated bpffs creator SID while the operation still uses the original token. For the CVSS the PR:L value is selected because exploitation requires local code execution and access to a usable BPF token path, but does not necessarily require full administrative privileges. AC:H reflects the need to win a file descriptor replacement race. This is a potential SELinux authorization bypass with no evidence of UAF, OOB access, arbitrary kernel writes, or direct network reachability. The paranoid score allows higher integrity impact if an unauthorized program load can be combined with otherwise permitted BPF use, while token restrictions, the BPF verifier, and later permission checks limit the supported impact. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 5.8 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. 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. The independent weaker Aegis shadow evaluated CVSS 0.0 and ActionableScore 1 with primitive class CLASS_C and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. The shadow agreed with the final production impact and aggregation did not change that impact. The final reported impact is MODERATE_KPANIC.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5)	MAYBE	BPF SIMPLEFIX LEAK LINUS  KPANIC INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
PrimitiveClass=CLASS_A
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
RequiresHostUID0=NO
AuthorizationDecisionBypass=YES
ProtectedResourceImpact=CONFIRMED
B4PendingReview=YES
B4PendingConfirmed=YES

1. ActionableScore

* Raw base score: 5.
* Conservative score: 5; no floor or cap applied.
* Raw paranoid score: 5.
* Paranoid score: 5; unsupported LPE or high-integrity consequences were not added.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

2. Signal breakdown

* +2 — Concrete authorization decision bypass: SELinux may check `avc_has_perm()` using the creator SID of a replacement fd object rather than the already-resolved token/path. An original DENY can therefore become ALLOW under the replacement SID.
* +2 — Strong semantic identity mismatch: BPF core continues using the original token while SELinux re-resolves the same numeric fd and may authorize against an unrelated bpffs superblock.
* +2 — Practical protected-resource access: the visible consumers are `BPF_MAP_CREATE` and `BPF_PROG_LOAD`, operations expressly protected by SELinux token permissions.
* +1 — Local below-host-admin trigger: the supplied evidence grounds a local delegated-token holder and a second thread sharing its fd table.
* -1 — Reduced/delegated authority is required: the attacker needs access to a usable BPF token path.
* -1 — Hard race: exploitation requires replacing the fd between core resolution and SELinux’s second lookup.

No UAF, OOB write, arbitrary kernel write, disclosure, verifier bypass, LPE, or C:H/I:H effect is shown. Later BPF restrictions and verifier checks remain applicable.

3. Reachability analysis

The grounded actor is a local process with delegated access to a usable BPF token, plus another thread sharing the fd table and racing fd replacement. Effective host-administrator power and host UID 0 are not required by the supplied evidence. The precise user-namespace scope of all BPF/token operations is not established, so `NamespaceScopedPrivilege=UNKNOWN`. No remote path is shown.

4. Primitive and severity reading

The primitive is a TOCTOU authorization mismatch, not memory corruption: resource resolution selects the original token, but SELinux may derive the authorization SID from a replacement object occupying the same fd number. The clean fix uses the resolved path or token’s stored `grantor_sid`.

The concrete DENY-to-ALLOW paths are `BPF_MAP_CREATE` through `selinux_bpf_map_create()` and `BPF_PROG_LOAD` through `selinux_bpf_prog_load()`. This supports B4-PENDING confirmation and CLASS_A authorization-bypass treatment. Protected BPF operations are confirmed, but privilege escalation or unrestricted BPF execution is not.

5. One-sentence report phrase

A shared-fd-table race can make SELinux authorize BPF map creation or program loading against an unrelated bpffs creator SID while BPF core uses the original token.

6. Manual review advice

MANUAL CHECK REQUIRED

Confirm policy combinations permitting the replacement SID while denying the original grantor SID, and assess the resulting BPF operation within the product’s token and verifier configuration.

7. Call-site confidence

Call-site confidence: high

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

Patch: selinux: fix BPF token permission checks
Commit: e1ef306ba20eb13099ca4463527890df67619405
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e1ef306ba20eb13099ca4463527890df67619405

Commit description:

Avoid multiple lookups of the bpffs creator SID using the token's file
descriptor when the same information can be found via the resolved
path/dentry (in selinux_bpf_token_create()) or the token itself (in
selinux_bpf_map_create() and selinux_bpf_prog_load()).  Not only does
this simplify the code, it avoids potential TOCTOU issues if the user
changes the token file descriptor passed into the kernel.

Cc: stable@vger.kernel.org
Fixes: 5473a72 ("selinux: add support for BPF token access control")
Reviewed-by: Stephen Smalley <stephen.smalley.work@gmail.com>
Tested-by: Stephen Smalley <stephen.smalley.work@gmail.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  security/selinux/hooks.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=e1ef306ba20eb13099ca4463527890df67619405

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

The original Linux kernel CVE announcement for CVE-2026-99129 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99129

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:N/I:L/A:L
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:H/A:L
  The Best / paranoid CVSS score: 5.8

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: 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).