* [CVE-2026-98196][MODERATE 7.0] wifi: brcmsmac: fix UAF in brcms_free_timer()
@ 2026-10-08 18:01 21% AL-KERNEL
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From: AL-KERNEL @ 2026-10-08 18:01 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-98196
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: wifi: brcmsmac: fix UAF in brcms_free_timer()
Commit: 10eeb0b29fd7f52487c9ae573e8d79c210a0095d
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=10eeb0b29fd7f52487c9ae573e8d79c210a0095d
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98196
Analysis date: Thu, 08 Oct 2026 14:01:52 -0400
ActionableScore: 4
ActionableScore lower bound: unknown
Actionable bucket: Borderline / manual review recommended
Manual review required: YES
Summary:
No one-sentence report phrase was found.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98196 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98196
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-2026-98196 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-98196 CHECK WITH IMPACT FROM ORIG NN IMPORTANT | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=4 LEGACY=MODERATE_KPANIC RESULT=SAME (legacy and Aegis reconciliation agree; 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:H/I:H/A:H';*CWE-416;CWE-362;CWE-667;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A race in brcms_free_timer() can cause use after free because brcms_del_timer() uses non synchronous delayed work cancellation and does not wait for an active _brcms_timer callback to finish. The timer structure can therefore be freed while the callback still derives and accesses the same object through container_of(). The confirmed impact is at least a local denial of service through a kernel crash. Reuse of the freed object while the callback continues to access timer fields may also permit kernel memory corruption or privilege escalation and requires manual review. For the CVSS the PR:L value is used for the paranoid score because delegated network administration or a restricted service may be able to initiate interface lifecycle operations without having full host control. Triggering requires brcmsmac hardware and a narrow race between delayed work execution and timer teardown, so AC:H is appropriate. The issue is not directly network reachable. Remote wireless traffic may influence callback timing but is not known to be sufficient to free the timer object.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 4) MAYBE REMOTE UAF NETWORK TIMER KPANIC KPANIC DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN5 - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=4
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
1. ActionableScore
* Raw conservative score: 2
* Conservative score: 4
* Raw paranoid score: 2
* Paranoid score: 4
* Applied conservative REAL UAF FLOOR 4: 2 -> 4
* Applied paranoid REAL UAF FLOOR 4: 2 -> 4
* Final recommended bucket: **Borderline / manual review recommended**::
2. Signal breakdown
* +2 Real UAF. `brcms_free_timer()` can free `t` while `_brcms_timer` is still executing and accessing that exact object.
* +1 Reliable kernel crash or strong DoS. Continued callback access after `kfree(t)` can realistically cause an invalid dereference or kernel fault.
* -1 Hard timing requirement. Freeing must overlap an already-running delayed-work callback during a timer teardown operation.
* No remote-reachability points. Wireless traffic alone is not shown to invoke `brcms_free_timer()`.
* No local-unprivileged point. The complete path that initiates timer destruction is not supplied.
* No strong or structured exploitation-leverage points. Controlled reclaim, attacker-shaped replacement contents, useful callback-field consumption after reuse, and arbitrary read or write are not demonstrated.
* No additional Availability point. It would duplicate the same UAF-induced crash.
* No Confidentiality or Integrity points. The supplied evidence does not establish disclosure or unauthorized modification.
* No concrete repeated-release/refcount point. There is one `kfree(t)` followed by stale callback access, not a second release or refcount mutation on `t`.
* Paranoid escalation was withheld because stronger exploitation would require an unproven reclaim or post-free object-control primitive.
Repeated-release checks:
* First operation can end lifetime: yes, `kfree(t)` ends the timer lifetime.
* Exact reference survives: the running work callback retains a derived reference to the same storage.
* Second operation mutates lifetime or refcount: no.
* Concrete repeated release/refcount +1: not awarded.
* Paranoid repeated-refcount +1: not awarded.
* FLOOR 5: not applicable because no second lifetime mutation or independently meaningful reuse leverage is established.
3. Reachability analysis
The vulnerable path requires a system using the `brcmsmac` driver and a timer callback executing concurrently with timer destruction. Compatible Broadcom wireless hardware and the loaded driver are prerequisites, but hardware-specific code alone does not justify a rare-hardware penalty.
The supplied patch does not expose the callers that ultimately reach `brcms_free_timer()`. Timer destruction is plausibly associated with driver teardown, interface lifecycle changes, initialization failure, or device removal, but the evidence does not establish whether an ordinary user, a delegated network-management service, or only a host administrator can drive the complete operation. Therefore `HostAdminRequired` and `NamespaceScopedPrivilege` remain `UNKNOWN`, and no privilege penalty or unprivileged-trigger bonus is applied.
Direct network triggering is not established. Wireless traffic may affect timer activity and callback timing, but it is not shown to initiate the required destruction of the timer. The race requires overlap with an in-flight callback and appears narrower than an ordinary repeatable data-path race.
4. Primitive and severity interpretation
The exact primitive is an asynchronous use-after-free of a `struct brcms_timer`: non-synchronous cancellation permits the delayed-work callback to remain active after the timer object is freed.
This is an active structured object rather than a passive buffer. However, the supplied evidence establishes only continued callback access to the stale object. It does not show controlled replacement, attacker-controlled post-free contents, function-pointer dispatch from reclaimed data, or another independently useful post-crash primitive.
This is therefore `CLASS_B`, but currently resembles a constrained teardown UAF rather than a strong Important-preserving UAF. The demonstrated consequence is kernel crash or DoS. Kernel memory corruption or privilege escalation is theoretically possible only if additional reclaim and stale-field-consumption mechanics exist, and those mechanics are not established here.
`ImportantCandidate=NO` because no meaningful exploitation leverage beyond the stale callback access and crash is demonstrated. `AutoDowngradeAllowed=YES` because this is not a repeated-release case, no security-boundary violation exists, and no controlled reuse or callback hijack is established. Manual review remains recommended because the missing `_brcms_timer` body and destruction call sites could reveal stronger stale-field use or less-privileged reachability.
5. One-sentence report phrase
A non-synchronous delayed-work cancellation allows an active brcmsmac timer callback to access a freed timer object, creating a timing-dependent local kernel UAF with demonstrated DoS potential but no established controlled-reuse or privilege-escalation primitive.
6. Manual review recommendation
MANUAL CHECK RECOMMENDED
Review `_brcms_timer()` and all `brcms_free_timer()` callers to determine which stale fields are consumed, whether any callback or pointer is dereferenced after free, and which actor can trigger timer teardown.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: wifi: brcmsmac: fix UAF in brcms_free_timer()
Commit: 10eeb0b29fd7f52487c9ae573e8d79c210a0095d
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=10eeb0b29fd7f52487c9ae573e8d79c210a0095d
Commit description:
brcms_free_timer() calls brcms_del_timer() which uses the non-synchronous
cancel_delayed_work() to cancel the timer's underlying delayed work. If
the work callback (_brcms_timer) is already running, cancel_delayed_work()
returns false without waiting, and brcms_free_timer() proceeds to kfree(t)
while the callback still accesses t through container_of().
Add an explicit cancel_delayed_work_sync() after brcms_del_timer() to
guarantee that any in-flight callback has completed before the timer
structure is freed.
Fixes: 5b435de ("net: wireless: add brcm80211 drivers")
Cc: [email protected]
Signed-off-by: Jiangshan Yi <[email protected]>
Acked-by: Arend van Spriel <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Johannes Berg <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
drivers/net/wireless/broadcom/brcm80211/brcmsmac/mac80211_if.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=10eeb0b29fd7f52487c9ae573e8d79c210a0095d
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98196 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98196
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:H/UI:N/S:U/C:N/I:N/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: 4
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
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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
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