[CVE-2026-53188][MODERATE 7.0] RDMA/core: Validate the passed in fops for ib_get_ucaps()

[CVE-2026-53188][MODERATE 7.0] RDMA/core: Validate the passed in fops for ib_get_ucaps()

[AL-KERNEL]

CVE: CVE-2026-53188
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: RDMA/core: Validate the passed in fops for ib_get_ucaps()
Commit: 96b6e98ff12d50ed5817230c6f1188e1150d225d
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=96b6e98ff12d50ed5817230c6f1188e1150d225d
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53188
Analysis date: Thu, 25 Jun 2026 07:50:27 -0400
ActionableScore: 5
ActionableScore lower bound: 3
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
RDMA UCAP fd validation relied only on dev_t, allowing a local user with a suitable char/block dev_t alias to masquerade a non UCAP fd as an authentic UCAP cdev and potentially bypass RDMA capability checks.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-53188 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53188

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-2026-53188	MODERATE	CHECK	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:N';CWE-863;CWE-284;CWE-287;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:N';BEST CVSS score: '6.3';DESCR 'RDMA UCAP validation accepted a file descriptor based only on the numeric dev_t value. A local user could potentially pass a non UCAP device fd with the same dev_t because character and block device numbers can alias, causing the fd to masquerade as an authentic UCAP cdev fd. For the CVSS the PR:L is used for the paranoid score because exploitation requires local code execution and access to a suitable device fd, but does not necessarily require full administrator privileges. The issue is not network reachable and is triggered through a local RDMA control path. Impact is primarily an access control or capability validation bypass. In the worst defensible case, incorrect UCAP acceptance may expose RDMA capabilities with confidentiality or integrity impact and should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4)	YES	SIMPLEFIX NETWORK HARDWARE  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	YES	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: +1. The issue is triggered through a local fd passed to the RDMA UCAP path.
* Cross-boundary isolation or policy bypass: +1. The bug bypasses the intended authenticity check for UCAP character-device fds by relying only on dev_t.
* Integrity impact plausible: +1. A masqueraded fd may cause incorrect UCAP capability acceptance and affect RDMA capability decisions.
* No memory corruption: +0. The patch shows validation of f_ops, not UAF, OOB, double-free, refcount misuse, or arbitrary write.
* Not network reachable: +0. This is a local control path, not packet-triggered.

Paranoid additional signals:

* Security-boundary bypass with practical sensitive-object access: +2 instead of only +1 policy-bypass weighting. UCAP is a capability-gating API, and accepting a non-UCAP fd as authentic may cross an intended permission boundary.
* Confidentiality impact plausible: +1. If the wrong UCAP mask exposes RDMA capabilities, sensitive RDMA objects or device capabilities may become visible or usable.
* Practical exploit chain strongly implied: +1. The commit explicitly describes a concrete masquerade condition using char/block dev_t aliasing.
* Special condition / constrained reachability: -1. Exploitation depends on finding or opening a block device with a colliding dev_t and on affected RDMA UCAP deployment.

## 3. Reachability analysis

A local process that can call the affected RDMA UCAP interface and provide an fd can trigger the validation flaw. The attacker does not need remote network reachability, and this is not a packet-processing bug. The required privilege is best treated as local user level for triage because the attacker may only need access to a suitable fd, not full host root. In some deployments access to block devices or RDMA device nodes may be restricted by permissions, cgroups, containers, or device ACLs, which reduces practical reachability.

Namespaces and containers matter because device-node exposure can differ from the host. A container or service account with delegated device access may not be fully privileged, so treating this as PR:H would likely understate the practical security-boundary issue. The path is not as broadly exposed as core networking or common filesystems, but RDMA uverbs deployments are security-sensitive when present.

## 4. Severity interpretation

This behaves more like an actionable access-control / capability-confusion bug than a generic memory-safety vulnerability. There is no evidence of memory corruption or direct LPE from the patch. The realistic impact depends on what UCAP capabilities can be incorrectly accepted after fd masquerading.

The conservative result is borderline Moderate because the exploit condition is specific and local. The paranoid result reaches Actionable Moderate because the bug crosses an intended RDMA capability boundary and may affect confidentiality or integrity depending on deployed UCAP policy.

## 5. One-sentence report phrase

RDMA UCAP fd validation relied only on dev_t, allowing a local user with a suitable char/block dev_t alias to masquerade a non UCAP fd as an authentic UCAP cdev and potentially bypass RDMA capability checks.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED.

The patch is not memory corruption, but it is a capability-boundary validation bug in RDMA core. The real severity depends on what an accepted UCAP mask enables in affected deployments, so it should not be auto-closed without subsystem-aware review.

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

Patch: RDMA/core: Validate the passed in fops for ib_get_ucaps()
Commit: 96b6e98ff12d50ed5817230c6f1188e1150d225d
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=96b6e98ff12d50ed5817230c6f1188e1150d225d

Commit description:

Sashiko pointed out it is not safe to rely only on the devt because
char/block alias so if the user finds a block device with the same dev_t
it can masquerade as a ucap cdev fd.

Test the f_ops to only accept authentic cdevs.

Link: https://patch.msgid.link/r/0-v1-fd9482545e37+1e25-ib_ucaps_fd_ops_jgg@nvidia.com
Cc: stable@vger.kernel.org
Fixes: 61e5168 ("RDMA/uverbs: Introduce UCAP (User CAPabilities) API")
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/infiniband/core/ucaps.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=96b6e98ff12d50ed5817230c6f1188e1150d225d

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

The original Linux kernel CVE announcement for CVE-2026-53188 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53188

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:N
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:N
  The Best / paranoid CVSS score: 6.3

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: 3
  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: NO
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).