* [CVE-2026-89969][MODERATE 7.0] nvmet-tcp: fix out-of-bounds write when receiving an over-long PDU
@ 2026-09-16 14:52 21% AL-KERNEL
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From: AL-KERNEL @ 2026-09-16 14:52 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-89969
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: nvmet-tcp: fix out-of-bounds write when receiving an over-long PDU
Commit: a3f0bcfbaf3312a5754d1ce020a07d394669eb25
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a3f0bcfbaf3312a5754d1ce020a07d394669eb25
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89969
Analysis date: Wed, 16 Sep 2026 10:52:50 -0400
ActionableScore: 8
ActionableScore lower bound: 7
Actionable bucket: Strong Important candidate
Manual review required: YES
Summary:
No one-sentence report phrase was found.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-89969 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89969
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-2026-89969 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-89969 CHECK WITH IMPACT FROM ORIG NN IMPORTANT Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H';*CWE-787;CWE-120;*CWE-20;Other CVSS 'AV:A/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '8.8';DESCR 'An out-of-bounds write in the NVMe/TCP target receive path can occur because nvmet_tcp_try_recv_pdu calculates the remaining PDU bytes using the declared header length and negotiated header digest without bounding the result against the fixed queue pdu buffer. A remote unauthenticated host that can reach the NVMe/TCP target can cause bytes to be written past the 128 byte receive buffer when an over-long control PDU is processed after header digest negotiation. For the CVSS the PR:N is used because no local account or victim side privileges are required beyond network reachability to the NVMe/TCP target listener. AV:A is used because NVMe/TCP targets are normally deployed on isolated storage or data center networks rather than the public Internet. Impact is at least denial of service via kernel memory corruption and in the paranoid case may include confidentiality or integrity impact because the primitive is a controlled kernel out-of-bounds write.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate (with actual score 8) YES REMOTE WRITE OOB NVME NETWORK LINUS KPANIC DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFKP NO NO checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=8
ActionableScoreLower=7
PrimitiveClass=CLASS_A
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
1. ActionableScore
* Raw conservative score: 6
* Conservative score: 7
* Applied conservative floor/cap: CLASS_A remote attacker-controlled kernel OOB write preservation floor 6 -> 7.
* Raw paranoid score: 7
* Paranoid score: 8
* Applied paranoid floor/cap: Strong remote unauthenticated kernel memory corruption preservation floor 7 -> 8.
* Final recommended bucket: **Strong Important candidate**::
2. Signal breakdown
Conservative positive signals:
* +2 Strong corruption primitive: attacker-controlled out-of-bounds write past fixed kernel receive buffer queue->pdu.
* +2 Remote reachable / directly network-triggerable: remote unauthenticated host can trigger via NVMe/TCP target protocol traffic when target listener is reachable.
* +1 Reliable kernel crash / strong DoS: kernel memory corruption in target receive path can realistically crash the host.
* +1 Integrity plausible: attacker-controlled bytes overwrite adjacent kernel state, specifically queue->hdr_digest and queue->data_digest fields.
Paranoid additional signal:
* +1 Weak exploitation leverage concern: the overwritten adjacent fields are active per-queue protocol state, so impact beyond an immediate crash remains unresolved and requires manual review.
Non-awarded signals:
* RealUAF not awarded: no stale lifetime or post-free object use is established.
* Concrete repeated release/refcount not awarded: no repeated put/release/free/refcount mutation exists.
* Controlled reclaim not demonstrated.
* Arbitrary or directed kernel write not demonstrated.
* Confidentiality not awarded: no read-back or disclosure path is established.
* Extra Availability not awarded: same crash/corruption path is already counted once.
* Local unprivileged trigger not awarded separately because the relevant trigger is network access, not local code execution.
* Broad/default subsystem bonus not awarded: NVMe/TCP target is important but usually storage-network scoped rather than universally exposed.
3. Reachability analysis
The evaluated attacker is a remote unauthenticated host with network reachability to an NVMe/TCP target listener. No local account on the victim and no host-admin-equivalent privilege are required for the protocol trigger, so HostAdminRequired=NO.
The trigger depends on NVMe/TCP target being enabled and reachable. In practice, NVMe/TCP targets are commonly deployed on isolated storage or data-center networks rather than the public Internet, but that is a deployment exposure constraint rather than a host privilege requirement. Namespace-scoped privilege is not relevant to the complete trigger chain.
No special physical hardware access is required beyond the target deployment. No race or narrow timing condition is required. The trigger is an ordered protocol-state sequence involving header digest negotiation and an over-long or duplicate control PDU before rejection.
4. Primitive and severity interpretation
The exact primitive is a remote attacker-controlled out-of-bounds write in the NVMe/TCP target receive path. nvmet_tcp_try_recv_pdu() calculates queue->left from hdr->hlen, queue->offset, and hdgst, then receives additional bytes into queue->pdu + queue->offset without first ensuring that the computed receive length fits within sizeof(queue->pdu).
This is active kernel memory corruption, not a UAF and not a pure crash-only NULL dereference. The overwrite is limited in size and location, but the bytes are attacker-controlled and the target is adjacent kernel per-queue state. Conservative impact is at least host DoS and kernel state corruption. Paranoid impact requires manual review because a remote controlled OOB write in a kernel network storage target can sometimes have consequences beyond the first observed crash even when arbitrary R/W is not yet demonstrated.
PrimitiveClass=CLASS_A because an attacker-influenced OOB write is directly established. ImportantCandidate=YES because this is a remote unauthenticated kernel memory corruption primitive. AutoDowngradeAllowed=NO because automatically closing or downgrading would discard a concrete controlled corruption primitive with unresolved exploitation leverage.
5. One-sentence report phrase
A remote unauthenticated host that can reach an NVMe/TCP target can send an over-long PDU after header digest negotiation and cause attacker-controlled bytes to be written past the fixed queue pdu buffer, leading to kernel memory corruption and at least denial of service.
6. Manual review recommendation
MANUAL CHECK REQUIRED
Reason: controlled remote kernel out-of-bounds write is established, and the overwrite affects adjacent active protocol state, so Important-class impact must be manually evaluated even though arbitrary read/write or LPE is not demonstrated.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: nvmet-tcp: fix out-of-bounds write when receiving an over-long PDU
Commit: a3f0bcfbaf3312a5754d1ce020a07d394669eb25
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a3f0bcfbaf3312a5754d1ce020a07d394669eb25
Commit description:
nvmet_tcp_try_recv_pdu() reads a PDU header into the fixed 128-byte
queue->pdu union, then computes the remaining payload length as
queue->left = hdr->hlen - queue->offset + hdgst;
and reads that many more bytes into &queue->pdu + queue->offset, without
ever bounding the result against sizeof(queue->pdu).
A struct nvme_tcp_icreq_pdu is itself 128 bytes, exactly the size of the
union. Once a header digest has been negotiated (hdgst = 4), a second
ICReq passes the hlen == nvmet_tcp_pdu_size() check but yields
queue->left = 128 - 8 + 4 = 124, so bytes 8..132 are written into the
128-byte buffer -- 4 bytes past its end, over queue->hdr_digest and
queue->data_digest. Those bytes are attacker-controlled (an ICReq
carries no digest), and the duplicate ICReq is only rejected later,
after the overflow. A remote unauthenticated host can thus corrupt
kernel memory adjacent to the receive buffer.
Reject any PDU whose declared length would read past the end of
queue->pdu before the second recv.
Fixes: 872d26a ("nvmet-tcp: add NVMe over TCP target driver")
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Shivam Kumar <[email protected]>
Cc: [email protected]
Reviewed-by: Sagi Grimberg <[email protected]>
Signed-off-by: Keith Busch <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
drivers/nvme/target/tcp.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=a3f0bcfbaf3312a5754d1ce020a07d394669eb25
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-89969 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89969
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:A/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H
The Best / paranoid CVSS vector: AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
The Best / paranoid CVSS score: 8.8
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: 7
Paranoid ActionableScore: 8
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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