* [CVE-2026-89445][MODERATE 7.0] iommufd: Fix UAF in selftest IOPF reporting
@ 2026-09-12 11:05 21% AL-KERNEL
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From: AL-KERNEL @ 2026-09-12 11:05 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-89445
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: iommufd: Fix UAF in selftest IOPF reporting
Commit: cab2895729516799384d48560e6fca105fb3f927
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=cab2895729516799384d48560e6fca105fb3f927
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89445
Analysis date: Sat, 12 Sep 2026 07:05:41 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES
Summary:
No one-sentence report phrase was found.
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ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-89445 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89445
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-2026-89445 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-89445 CHECK WITH IMPACT FROM ORIG NN MODERATE 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:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A race in iommufd selftest IOPF reporting can cause a use-after-free because TRIGGER_IOPF borrows an attach handle from group pasid_array without synchronizing against PASID detach or replace. A local process with access to the iommufd selftest interface can race fault reporting with detach so iommu_report_device_fault or later code dereferences a freed iommufd_attach_handle and its domain pointer. For the CVSS the PR:L is used because the attacker needs local code execution and access to the iommufd selftest control path, but does not necessarily need full administrative privileges if that interface is exposed to the user. The issue is not network reachable and is triggered through local ioctls or selftest operations rather than packet traffic. Impact is at least a local denial of service via kernel crash and in the paranoid case may allow confidentiality or integrity impact due to kernel use-after-free memory corruption. Exposure is limited because the affected code is in the iommufd selftest mock device path, so production risk depends on whether this test interface is built and accessible.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5) YES INIT UAF HARDWARE KPANIC YES NO checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=5
ActionableScoreLower=4
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
1. ActionableScore
* Raw conservative score: 3
* Conservative score: 4. REAL UAF FLOOR 4 applied, 3 -> 4.
* Raw paranoid score: 4
* Paranoid score: 5. REAL UAF FLOOR 5 applied, 4 -> 5.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::
2. Signal breakdown
Conservative signals:
* +2 Real UAF / active lifetime violation. TRIGGER_IOPF can borrow an attach handle from group->pasid_array while concurrent PASID detach erases the handle and frees struct iommufd_attach_handle.
* +1 Reliable kernel crash / strong DoS. The stale handle or its domain pointer can be dereferenced during iommu_report_device_fault or later TRIGGER_IOPF processing.
* +1 Attacker-influenced active-object lifetime manipulation. The same selftest control path exposes trigger, attach, detach, and replace style operations, so a caller with access can drive the conflicting lifetime sequence.
* -1 Rare and difficult-to-reach test path. The affected code is in drivers/iommu/iommufd/selftest.c and depends on the iommufd selftest mock-device interface rather than a normal production IOMMU driver path.
Paranoid-only signal:
* +1 Structured stale-object exploitation leverage. The stale object is an active structured attach handle and the stale path consumes its domain pointer inside IOPF fault reporting, which is more than a passive cleanup-only stale dereference.
Non-awarded material signals:
* +2 Strong exploitation leverage not awarded. No controlled reclaim, attacker-shaped replacement object, arbitrary host kernel read/write, callback control, or demonstrated LPE is supplied.
* Concrete repeated release/refcount +1 not awarded. The patch establishes detach/free followed by stale dereference, not a second put/release/refcount mutation on the exact same dangling reference.
* Extra Availability +1 not awarded. The same kernel crash is already counted as reliable DoS.
* Confidentiality and Integrity points not awarded directly. UAF makes C/I a review concern, but no concrete disclosure, arbitrary write, credential manipulation, or protected-object modification is demonstrated.
* Race penalty not applied. Although the bug is a race, the supplied operations appear repeatable through the selftest interface rather than a one-shot externally uncontrollable timing window.
* Remote reachability not awarded. This is a local iommufd selftest ioctl/control path, not packet-triggered or network-facing.
Repeated release/refcount checklist:
* First release can end lifetime: yes, PASID detach can erase the handle and free struct iommufd_attach_handle.
* Exact same reference survives: yes for stale dereference purposes, because TRIGGER_IOPF borrowed the handle without synchronization.
* Second operation is a real lifetime/refcount mutation: no, the described stale operation is dereference/use of the freed handle/domain pointer.
* Concrete repeated release/refcount +1 awarded: no.
* Paranoid repeated-refcount leverage +1 awarded: no.
* FLOOR 5 applied: yes, but due active structured UAF with nontrivial stale domain-pointer consumption, not due repeated release/refcount.
3. Reachability analysis
The direct trigger is local and tied to the iommufd selftest mock-device interface. A caller needs access to the selftest control path that can issue TRIGGER_IOPF and concurrently perform PASID attach, detach, or replace operations.
Host-admin-equivalent privilege is not positively established from the supplied input, but below-host-admin reachability is also not fully proven. Therefore HostAdminRequired is UNKNOWN. The issue is not namespace-scoped in the supplied evidence, and there is no indication that the complete trigger chain can be performed solely through attacker-created user or network namespaces.
There is likely a prior configuration/build prerequisite because the affected file is iommufd selftest code. This materially limits production exposure. No special physical hardware is required in the supplied evidence because this is a mock-device selftest path.
The race is between IOPF fault reporting and PASID detach or replacement. It appears repeatable by a process that can drive the relevant selftest operations, so no hard-race penalty is applied.
4. Primitive and severity interpretation
The exact primitive is a real kernel use-after-free of an iommufd_attach_handle. The stale reference is an active structured object, not fixed stale storage. The stale path can consume the freed handle and its domain pointer during iommu_report_device_fault or later TRIGGER_IOPF processing.
This is not an ordinary cleanup-only stale dereference. It is an active reporting path racing with attach-handle lifetime changes. However, it is also not CLASS_A because controlled reclaim, object substitution, arbitrary R/W, callback control, refcount takeover, or demonstrated privilege escalation are not established.
PrimitiveClass is CLASS_B. The demonstrated consequence is local kernel crash / DoS. The speculative consequence is stronger exploitation from kernel UAF if the stale handle storage can be usefully reclaimed or if domain-pointer consumption can be shaped, but that is not proven by the patch.
ImportantCandidate is YES because a real active structured UAF exists and exploitation leverage beyond crash remains unresolved. AutoDowngradeAllowed is NO because automatically closing this as ordinary Moderate would discard a concrete kernel lifetime primitive with unresolved post-lifetime behavior, despite the selftest exposure limitation.
Likely operational severity is Actionable Moderate in most production triage due the selftest-only path, with Strong Important review justified if the selftest interface is built and reachable by untrusted local users.
5. One-sentence report phrase
A race in iommufd selftest IOPF reporting lets TRIGGER_IOPF use an attach handle after concurrent PASID detach frees it, causing at least a local kernel crash and requiring manual review because the stale active handle and domain pointer are consumed after lifetime end.
6. Manual review recommendation
MANUAL CHECK REQUIRED
Reason: the patch explicitly fixes a real UAF in kernel code, and although exposure is limited to the iommufd selftest mock-device path, the stale object is active structured state consumed during IOPF reporting.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: iommufd: Fix UAF in selftest IOPF reporting
Commit: cab2895729516799384d48560e6fca105fb3f927
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=cab2895729516799384d48560e6fca105fb3f927
Commit description:
IOMMUFD selftest TRIGGER_IOPF borrows an attach handle from
group->pasid_array without synchronizing against PASID detach,
then a concurrent iommu_report_device_fault() can dereference
that borrowed handle's domain pointer after the detach erases
the handle and frees the backing struct iommufd_attach_handle.
TRIGGER_IOPF then dereferences the freed handle, causing a UAF.
Fix by adding a iopf_rwsem in mock_dev to follow the expected design
of a real driver. Hold its read side across the whole
iommu_report_device_fault() call, and its write side around every
path that attaches, detaches, or replaces a device domain.
This can block new reports and drains in-flight reports before an old
attach handle or the IOPF fault parameter can be removed.
Also take the write side while registering a mock device, since
it can invoke the mock driver's default-domain attach callback.
Closes: https://lore.kernel.org/all/D5E3AA41600B2056+f4e15662-bd2b-43ea-91cb-518de429e72c@smail.nju.edu.cn/
Fixes: ddee199 ("iommufd/selftest: Add IOPF support for mock device")
Cc: [email protected]
Suggested-by: Jason Gunthorpe <[email protected]>
Assisted-by: Codex:gpt-5.6-terra
Signed-off-by: Peiyang He <[email protected]>
Link: https://patch.msgid.link/38C8DF0A118B7176+20260811095551.2756745-1-peiyang_he@smail.nju.edu.cn
Signed-off-by: Jason Gunthorpe <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
drivers/iommu/iommufd/selftest.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=cab2895729516799384d48560e6fca105fb3f927
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-89445 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89445
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: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: 4
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.
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