* [CVE-2026-92508][MODERATE 7.0] RDMA/core: Fix potential use after free in ib_free_cq() [ Upstream
@ 2026-09-18 8:54 21% AL-KERNEL
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From: AL-KERNEL @ 2026-09-18 8:54 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-92508
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: RDMA/core: Fix potential use after free in ib_free_cq() [ Upstream
Commit: a804b162f9bc2b38b2ed1b4752eea9faadb1645b
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a804b162f9bc2b38b2ed1b4752eea9faadb1645b
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-92508
Analysis date: Fri, 18 Sep 2026 04:54:15 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES
Summary:
A race in RDMA core `ib_free_cq()` can leave a completion queue visible through restrack while vendor-specific CQ resources are being destroyed, allowing local RDMA netlink access to hit a potential use-after-free and cause at least a kernel crash.
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ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-92508 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-92508
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-2026-92508 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-92508 CHECK WITH IMPACT FROM ORIG NN IMPORTANT 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-664;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A race in RDMA core ib_free_cq can leave a completion queue visible through restrack while vendor specific CQ resources are already being destroyed or freed. A local process using the RDMA netlink restrack path may acquire a reference during this teardown window and access a CQ whose internal resources are no longer valid, creating a potential use after free condition. For the CVSS the PR:L is used because reliable triggering requires a local user or process with access to RDMA objects or RDMA netlink, but not necessarily full administrator privileges in all deployments. The issue is not directly network reachable because the vulnerable access path is local netlink control plane handling rather than RDMA packet traffic. Impact is at least local denial of service via kernel crash and in the paranoid case may include confidentiality or integrity impact due to the UAF class, so this should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5) YES UAF NETWORK LINUS KPANIC KPANIC DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN6 NO NO checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=5
ActionableScoreLower=4
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
## 1. ActionableScore
* Raw conservative score: 3
* Conservative score: 4
* Raw paranoid score: 5
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::
Conservative floor applied: 3 -> 4 because a real active-object lifetime violation is directly implied and host-admin-equivalent privilege is not positively established.
No paranoid floor or cap was applied.
## 2. Signal breakdown
Conservative signals:
* +2 Real UAF / active lifetime violation. The CQ can remain reachable through RDMA restrack while vendor-specific CQ resources are already freed during `ib_free_cq()`.
* +1 Secondary registry / restrack staleness. The stale object remains discoverable through the restrack index until `rdma_restrack_del()` runs.
* +1 Reliable kernel crash / strong DoS concern. Netlink access to a CQ whose internal resources are already freed can realistically produce a kernel fault.
* -1 Hard timing window. The commit explicitly describes a short window during CQ destruction.
Conservative raw score: 2 + 1 + 1 - 1 = 3.
Conservative floor: 3 -> 4.
Paranoid signals:
* +2 Real UAF / active lifetime violation.
* +1 Secondary registry / restrack staleness.
* +1 Reliable kernel crash / strong DoS concern.
* +1 Repeatable active-object lifetime concern. A local RDMA-capable process may be able to exercise CQ teardown and concurrent restrack/netlink inspection repeatedly, making this stronger than a one-shot internal cleanup fault.
Paranoid raw score: 2 + 1 + 1 + 1 = 5.
Paranoid score: 5.
Important non-awarded signals:
* Controlled reclaim is not demonstrated.
* Arbitrary kernel read/write is not demonstrated.
* Callback or function-pointer control is not demonstrated.
* Direct remote network reachability is not established.
* Confidentiality and integrity are not awarded as independent ActionableScore signals merely because a UAF exists.
* Structured stale-object leverage is not separately awarded beyond the restrack/lifetime mechanism because attacker-shaped replacement contents are not shown.
* Concrete repeated release/refcount signal is not awarded.
Repeated-release/refcount check:
* First release can end lifetime: not established for the same exact reference in the supplied control flow.
* Exact same reference survives to a second lifetime mutation: not established.
* Second operation is a concrete lifetime/refcount mutation: not established.
* +1 Concrete repeated release/refcount awarded: no.
* Paranoid repeated-refcount leverage +1 awarded: no.
* FLOOR 5 from repeated release/refcount: not applied.
## 3. Reachability analysis
The vulnerable access path is local RDMA netlink/restrack control-plane access, not RDMA packet traffic. A remote network packet alone is not shown to reach `ib_free_cq()` or `rdma_restrack_get()` in the vulnerable way.
The likely attacker is a local process able to access RDMA objects or RDMA restrack information. The supplied evidence does not fully resolve whether this requires host-admin-equivalent privilege, a delegated RDMA management right, device-node access, or ordinary user access in a specific deployment. Therefore `HostAdminRequired=UNKNOWN`.
Namespace scoping is also unresolved. The input does not prove that the complete trigger chain is available with attacker-created namespaces or namespace-scoped capabilities. Therefore `NamespaceScopedPrivilege=UNKNOWN`.
Prior setup may include the presence of an RDMA device and RDMA userspace access. This is a real deployment condition, but not enough by itself to apply a rare-hardware or host-admin penalty. The timing window is short, but local repeated attempts against CQ teardown and restrack enumeration are technically plausible.
## 4. Primitive and severity interpretation
The exact primitive is a lifetime-ordering bug: `rdma_restrack_del(&cq->res)` was performed after vendor-specific CQ destruction, leaving the CQ visible to restrack users while internal resources may already be released.
This is an active structured object UAF candidate, not fixed stale storage. The stale object is a CQ registered in a kernel tracking structure and reachable via a netlink inspection path. The demonstrated consequence is primarily kernel crash or local DoS.
This is not merely an ordinary stale cleanup dereference because the object remains externally discoverable through restrack during teardown. However, the patch does not establish controlled reclaim, attacker-controlled replacement contents, arbitrary write, or a proven LPE chain. Therefore it is `PrimitiveClass=CLASS_B`, not `CLASS_A`.
ImportantCandidate is YES because a real active-object UAF remains reachable through a kernel registry/control-plane path and the exploitation leverage is not fully resolved. AutoDowngradeAllowed is NO because automatically closing this as ordinary DoS would discard a concrete unresolved kernel lifetime primitive.
Likely operational severity: Actionable Moderate, with Important-class review justified if product context shows below-host-admin RDMA netlink access or practical repeated triggering.
## 5. One-sentence report phrase
A race in RDMA core `ib_free_cq()` can leave a completion queue visible through restrack while vendor-specific CQ resources are being destroyed, allowing local RDMA netlink access to hit a potential use-after-free and cause at least a kernel crash.
## 6. Manual review recommendation
MANUAL CHECK REQUIRED
Reason: the patch explicitly fixes a potential UAF in an active RDMA core object reachable through restrack/netlink, and the exact privilege boundary plus vendor-driver exploitation leverage require product-specific review.
## 7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: RDMA/core: Fix potential use after free in ib_free_cq() [ Upstream
Commit: a804b162f9bc2b38b2ed1b4752eea9faadb1645b
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a804b162f9bc2b38b2ed1b4752eea9faadb1645b
Changed files:
drivers/infiniband/core/cq.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=a804b162f9bc2b38b2ed1b4752eea9faadb1645b
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-92508 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-92508
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:L/I:L/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.
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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