[CVE-2026-63988][LOW] bridge: Fix sleep in atomic context in sysfs path [ Upstream

[CVE-2026-63988][LOW] bridge: Fix sleep in atomic context in sysfs path [ Upstream

[AL-KERNEL]

CVE: CVE-2026-63988
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: bridge: Fix sleep in atomic context in sysfs path [ Upstream
Commit: e976e3f2f2005c6267089a1a3b6344f234a59a55
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e976e3f2f2005c6267089a1a3b6344f234a59a55
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63988
Analysis date: Sun, 19 Jul 2026 19:12:53 -0400
ActionableScore: 1
ActionableScore lower bound: 0
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-63988 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63988

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-2026-63988	LOW	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:N/I:N/A:H';CWE-667;*CWE-833;CWE-754;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 sleep in atomic context can be triggered in the Linux bridge sysfs path because brport_store() held the bridge spinlock while processing port attributes that may call sleeping networking helpers such as dev_set_promiscuity(). A local actor who can modify bridge port sysfs attributes can trigger a kernel warning and in some configurations a denial of service, especially when panic_on_warn is enabled or when the invalid locking context causes a stall. For the CVSS the PR:L is used for the paranoid score because some deployments delegate bridge or netadmin control to container root or service accounts, while the typical base case requires administrator level network configuration rights. The issue is not network reachable and is triggered through local control plane configuration writes rather than packet traffic. Impact is availability only, with no evidence of memory corruption, information disclosure, or privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 1)  SKIP CVE-2026-63988 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: 78cd408356fe3edbac66598772fd347bf3e32c1f YES  NO NO unknown 	MAYBE	LOCK DANGER HARDWARE  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	-	-	checked

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

1. ActionableScore

ActionableScore=1
ActionableScoreLower=0

* Conservative score: 0
* Paranoid score: 1
* Final recommended bucket: **Ordinary Moderate / Low-like**::

2. Signal breakdown

Conservative signals:

* Reliable crash / strong DoS: +0. The patch shows a sleeping-in-atomic warning/splat, not a demonstrated panic, UAF, OOB access, double-free, or persistent corruption.
* Requires admin/root/CAP_NET_ADMIN in typical deployments: -2. Writing bridge port sysfs attributes normally requires administrative network configuration privileges.
* Final conservative score is floored at 0.

Paranoid signals:

* Reliable kernel crash / strong DoS concern: +1. If `panic_on_warn` is enabled, or if the invalid locking context causes a stall, this can become a local availability issue.
* Broad/common subsystem exposure: +1. Linux bridge is commonly deployed, but the affected path is still a local control-plane sysfs path.
* Reduced privilege / delegated netadmin interpretation: -1. In containerized or delegated environments, bridge or netadmin control may be given to a less trusted actor than full host root.
* No memory corruption: +0. The patch only narrows spinlock scope and does not show UAF, OOB write, stale pointer reuse, type confusion, or refcount misuse.
* No privilege escalation: +0. No confidentiality or integrity primitive is supported by the patch.

Call-site confidence: high. The relevant call path is shown directly in the trace and diff: `brport_store()` -> port attribute store -> `br_port_flags_change()` -> `br_manage_promisc()` -> `dev_set_promiscuity()`.

3. Reachability analysis

The bug is triggered by local writes to bridge port sysfs attributes. In normal deployments this requires root or `CAP_NET_ADMIN`, because creating and configuring bridge ports is administrative network control. It is not packet-triggered and is not remotely reachable through normal bridge forwarding traffic. Namespaces or containers can matter if a container root or service account receives delegated network administration rights, but that is a deployment-specific privilege reduction rather than a true unprivileged trigger.

4. Severity interpretation

This behaves like an ordinary Moderate or Low-like local privileged DoS issue. The realistic impact is a warning/splat and possible availability impact under `panic_on_warn` or related debug/hardening configurations. There is no demonstrated memory corruption, privilege escalation, information disclosure, or cross-boundary policy bypass. The paranoid score is only slightly higher because delegated netadmin environments can make the trigger more operationally relevant.

5. One-sentence report phrase

A local actor with bridge port configuration privileges can trigger a sleep-in-atomic warning in the bridge sysfs path when changing port attributes that call `dev_set_promiscuity()`, with impact limited to local denial of service in configurations where such warnings panic or stall the kernel.

6. Manual review recommendation

NO MANUAL CHECK NEEDED

This should not be auto-escalated to Important-class handling. The patch fixes an invalid locking context in a privileged local control-plane path, with no evidence of memory corruption or privilege escalation.

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

Patch: bridge: Fix sleep in atomic context in sysfs path [ Upstream
Commit: e976e3f2f2005c6267089a1a3b6344f234a59a55
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e976e3f2f2005c6267089a1a3b6344f234a59a55

Changed files:
  net/core/dev_addr_lists.c
  fs/read_write.c
  fs/kernfs/file.c
  net/bridge/br_sysfs_if.c
  include/linux/spinlock.h
  lib/dump_stack.c
  kernel/sched/core.c
  net/core/dev_api.c
  net/bridge/br_if.c
  arch/x86/entry/syscall_64.c
  arch/x86/entry/entry_64.S
  net/bridge/br_switchdev.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=e976e3f2f2005c6267089a1a3b6344f234a59a55

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

The original Linux kernel CVE announcement for CVE-2026-63988 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63988

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: 0
  Paranoid ActionableScore: 1

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 alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).