[CVE-2026-46133][MODERATE 7.0] RDMA/rxe: Reject unknown opcodes before ICRC processing

[CVE-2026-46133][MODERATE 7.0] RDMA/rxe: Reject unknown opcodes before ICRC processing

[AL-KERNEL]

CVE: CVE-2026-46133
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: RDMA/rxe: Reject unknown opcodes before ICRC processing
Commit: e3dc3a2fb05f4ed49c7f20594c4c52350d032189
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e3dc3a2fb05f4ed49c7f20594c4c52350d032189
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46133
Analysis date: Thu, 28 May 2026 13:25:36 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
Soft RoCE RXE can allow a single unauthenticated UDP packet with an unknown BTH opcode to trigger an ICRC length underflow and OOB read, leading to a remotely reachable kernel panic when RXE is configured.

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

The original Linux kernel CVE announcement for CVE-2026-46133 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46133

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-2026-46133	MODERATE	CHECK	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H';CWE-125;CWE-190;*CWE-20;Other CVSS 'AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '8.2';DESCR 'Soft RoCE RXE can process an unauthenticated UDP packet with an unknown BTH opcode before rejecting the opcode. Because the rxe_opcode array entry for an unknown opcode is zero initialized, length arithmetic in ICRC processing can underflow and pass a huge size to rxe_crc32(), causing an out-of-bounds read of skb payload memory. For the CVSS the PR:N is used because a remote sender only needs network reachability to the RXE UDP port when an RXE device is configured. The issue is network reachable, but practical exposure requires Soft RoCE to be enabled and an rxe link to exist. Impact is primarily denial of service via kernel panic. The paranoid score includes low confidentiality impact because the primitive is a real OOB read, but no user visible disclosure or write primitive is shown.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5) 	MAYBE	READ KASAN OOB INIT NETWORK SKB KPANIC PACKET  KPANIC INCREASED_TO_MODERATE7_BASED_ON_GUESSCVSS	-	-	checked

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

ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: **4**
* Paranoid score: **5**
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

* Remote reachable / network-triggerable: **+2**. A single unauthenticated UDP packet to the RXE RoCE UDP port can trigger the vulnerable path when an RXE device is configured.
* Reliable kernel crash / strong DoS: **+1**. The commit message reports KASAN OOB read and later kernel panic from repeated packets.
* Availability impact realistic: **+1**. The practical demonstrated impact is kernel panic / system DoS.
* Confidentiality impact plausible, paranoid only: **+1**. The primitive is a real OOB read during CRC processing, but no user-visible disclosure path is shown.
* Weak read-only OOB: **+0**. This is not an OOB write, UAF, double-free, or controlled overwrite.
* No LPE signal: **+0**. The patch does not support privilege escalation or integrity impact.
* Configuration-dependent exposure: **0**. Soft RoCE RXE must be enabled and an RXE link must exist, but once configured the trigger is unauthenticated network input, so I would not downgrade below manual-review range.

## 3. Reachability analysis

The trigger is a malformed RoCE/RDMA UDP packet with an unknown BTH opcode. No QP, connection, or authentication is required after the RXE module is loaded and an `rxe` link is created. This is not a default path on all systems, but it is a real network receive path on systems using Soft RoCE. Namespaces may matter if an attacker can reach the RXE UDP port from a container or adjacent network, but no local account on the target is required for the network trigger.

## 4. Severity interpretation

This behaves like an **Actionable Moderate** issue. The realistic demonstrated impact is unauthenticated remote DoS through a kernel panic. The OOB read is real, but it is used internally by CRC calculation and there is no demonstrated information leak, write primitive, or privilege escalation path. It should not be treated as Important memory corruption, but it also should not be auto-closed as a low-risk functional bug.

## 5. One-sentence report phrase

Soft RoCE RXE can allow a single unauthenticated UDP packet with an unknown BTH opcode to trigger an ICRC length underflow and OOB read, leading to a remotely reachable kernel panic when RXE is configured.

## 6. Manual review recommendation

**MANUAL CHECK REQUIRED**

Manual review is required because this is unauthenticated network-triggerable kernel OOB read with demonstrated panic, even though exploitation appears limited to DoS and depends on RXE being configured.

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

Patch: RDMA/rxe: Reject unknown opcodes before ICRC processing
Commit: e3dc3a2fb05f4ed49c7f20594c4c52350d032189
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e3dc3a2fb05f4ed49c7f20594c4c52350d032189

Commit description:

Even after applying commit 7244491 ("RDMA/rxe: Validate pad and ICRC
before payload_size() in rxe_rcv"), a single unauthenticated UDP packet
can still trigger panic.  That patch handled payload_size() underflow only
for valid opcodes with short packets, not for packets carrying an unknown
opcode.  The unknown-opcode OOB read described below predates that commit
and reaches back to the initial Soft RoCE driver.

The check added there reads

    pkt->paylen < header_size(pkt) + bth_pad(pkt) + RXE_ICRC_SIZE

where header_size(pkt) expands to rxe_opcode[pkt->opcode].length.  The
rxe_opcode[] array has 256 entries but is only populated for defined IB
opcodes; any other entry (for example opcode 0xff) is zero-initialized, so
length == 0 and the check degenerates to

    pkt->paylen < 0 + bth_pad(pkt) + RXE_ICRC_SIZE

which does not constrain pkt->paylen enough.  rxe_icrc_hdr() then computes

    rxe_opcode[pkt->opcode].length - RXE_BTH_BYTES

which underflows when length == 0 and passes a huge value to rxe_crc32(),
causing an out-of-bounds read of the skb payload.

Reproduced on v7.0-rc7 with that fix applied, QEMU/KVM with
CONFIG_RDMA_RXE=y and CONFIG_KASAN=y, after

    rdma link add rxe0 type rxe netdev eth0

A single 48-byte UDP packet to port 4791 with BTH opcode=0xff and
QPN=IB_MULTICAST_QPN triggers:

    BUG: KASAN: slab-out-of-bounds in crc32_le+0x115/0x170
    Read of size 1 at addr ...
    The buggy address is located 0 bytes to the right of
     allocated 704-byte region
    Call Trace:
     crc32_le+0x115/0x170
     rxe_icrc_hdr.isra.0+0x226/0x300
     rxe_icrc_check+0x13f/0x3a0
     rxe_rcv+0x6e1/0x16e0
     rxe_udp_encap_recv+0x20a/0x320
     udp_queue_rcv_one_skb+0x7ed/0x12c0

Subsequent packets with the same shape fault on unmapped memory and panic
the kernel.  The trigger requires only module load and "rdma link add"; no
QP, no connection, and no authentication.

Fix this by rejecting packets whose opcode has no rxe_opcode[] entry,
detected via the zero mask or zero length, before any length arithmetic
runs.

Cc: stable@vger.kernel.org
Fixes: 8700e3e ("Soft RoCE driver")
Link: https://patch.msgid.link/r/20260414111555.3386793-1-michael.bommarito@gmail.com
Assisted-by: Claude:claude-opus-4-6
Signed-off-by: Michael Bommarito <michael.bommarito@gmail.com>
Reviewed-by: Zhu Yanjun <yanjun.zhu@linux.dev>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/infiniband/sw/rxe/rxe_recv.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=e3dc3a2fb05f4ed49c7f20594c4c52350d032189

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

The original Linux kernel CVE announcement for CVE-2026-46133 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46133

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:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H
  The Best / paranoid CVSS score: 8.2

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