* [CVE-2026-89483][MODERATE REGULAR] nvme: zero the discard fallback page
@ 2026-09-12 2:53 21% AL-KERNEL
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From: AL-KERNEL @ 2026-09-12 2:53 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-89483
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: nvme: zero the discard fallback page
Commit: dc4d4b70a863f7e39ef8bd137634be4e6db8b084
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=dc4d4b70a863f7e39ef8bd137634be4e6db8b084
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89483
Analysis date: Fri, 11 Sep 2026 22:53:31 -0400
ActionableScore: 3
ActionableScore lower bound: 2
Actionable bucket: Borderline / manual review recommended
Manual review required: YES
Summary:
No one-sentence report phrase was found.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-89483 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89483
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 REGULAR
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-2026-89483 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-89483 CHECK WITH IMPACT FROM ORIG NN MODERATE Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N';CWE-908;*CWE-200;CWE-226;Other CVSS 'AV:A/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:N';BEST CVSS score: '4.8';DESCR 'An uninitialized memory disclosure can occur in the NVMe discard fallback path because nvme_setup_discard maps a full 4096 byte DSM payload while a single discard range initializes only the first 16 bytes. If the normal zeroed allocation fails under memory pressure, the code falls back to ctrl discard_page which was allocated without zeroing and may contain stale kernel memory. The extra bytes can be handed to an NVMe controller or to an NVMe/TCP storage target, and KMSAN showed uninitialized data including kernel memory related contents. For the CVSS the PR:L is used for the paranoid score because reliable triggering usually requires a local user or service that can cause discard operations and memory pressure, although some deployments may restrict such operations to administrators. The issue is not directly reachable from the public Internet. In practice exploitation is most relevant when a malicious or compromised NVMe device or NVMe/TCP target can observe the DSM payload on a local storage or data center network. Impact is primarily confidentiality loss through kernel memory disclosure, with no supported integrity or availability impact and no demonstrated privilege escalation primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 3) YES READ KASAN SIMPLEFIX NVME LEAK HARDWARE LINUS MEMORY DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 NO NO checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=3
ActionableScoreLower=2
PrimitiveClass=NONE
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
1. ActionableScore
* Raw conservative score: 2
* Conservative score: 2
* Raw paranoid score: 3
* Paranoid score: 3
* Final recommended bucket: **Borderline / manual review recommended**::
No floor or cap was applied.
2. Signal breakdown
Conservative signals:
* +1 Confidentiality plausible: the fallback discard page may contain uninitialized stale kernel memory and those bytes are handed to the NVMe controller or NVMe/TCP target.
* +1 Important storage path: the issue is in the NVMe discard path and affects data sent through the block/storage stack.
Paranoid additional signal:
* +1 Kernel pointer disclosure sensitivity: KMSAN evidence shows the leaked tail can contain kernel-memory-related contents such as vmemmap struct page pointers. This supports manual sensitivity, but not Important-class scoring by itself.
Non-awarded signals:
* +0 RealUAF not awarded: no use-after-free, stale object lifetime violation, double release, or refcount mutation is established.
* +0 Memory corruption not awarded: the patch fixes uninitialized data exposure, not an overwrite, UAF, OOB write, or object corruption.
* +0 Integrity not awarded: no unauthorized modification of kernel state, storage data, credentials, or policy is shown.
* +0 Availability not awarded: no crash, panic, persistent DoS, or resource exhaustion is the primary consequence.
* +0 Remote reachable not awarded: the supplied text explicitly says it is not remotely triggerable. A malicious NVMe/TCP target may observe leaked bytes, but does not directly trigger the vulnerable operation.
* +0 Strong disclosure / CLASS_A not awarded: the disclosure is bounded and conditional on fallback allocation behavior under memory pressure, not a broad or controlled kernel memory read primitive.
* No negative host-admin penalty was applied because complete host-admin requirement is not positively established.
* No race/timing penalty was applied because this is not a timing race.
3. Reachability analysis
The vulnerable path is reached when `nvme_setup_discard()` uses `ctrl->discard_page` as a fallback after `kzalloc(GFP_ATOMIC | __GFP_NOWARN)` fails. The supplied evidence states that reaching this path requires memory pressure.
The attacker model is not fully resolved. A local user or local service may be able to influence discard activity and memory pressure in some configurations, but the complete below-host-admin trigger is not proven from the supplied input. Host-admin-equivalent privilege is also not positively established as mandatory for the complete vulnerable operation, so `HostAdminRequired=UNKNOWN`.
The issue is not directly remotely triggerable. In NVMe/TCP deployments, the leaked DSM payload may be visible to a remote storage target on a storage or data-center network, but the remote target is primarily an observer of leaked data rather than the direct trigger. No namespace-scoped capability path is established.
4. Primitive and severity interpretation
The exact primitive is an uninitialized kernel memory disclosure to an NVMe controller or NVMe/TCP target. A single-range discard initializes only the first 16 bytes, while the code maps a full 4096-byte DSM payload. If the normal zeroed allocation fails, the fallback page was previously allocated without `__GFP_ZERO`, so unused bytes could contain stale kernel memory.
This is fixed stale storage, not an active structured UAF. There is no concrete repeated release/refcount operation. There is no first lifetime operation that may free an object followed by a second lifetime mutation. The demonstrated consequence is confidentiality exposure of stale kernel memory bytes.
PrimitiveClass is `NONE` because no kernel corruption, ownership violation, authorization bypass, UAF, or active lifetime primitive is established. The issue is still security-relevant as an information leak, but the evidence does not support Important-class classification. `ImportantCandidate=NO` because there is no controlled kernel read, no LPE path, no arbitrary R/W, and no memory corruption. `AutoDowngradeAllowed=YES` because no unresolved Class A or Class B primitive remains, though environment-specific manual review is useful.
Operationally this is a low-to-borderline Moderate information leak. It is most relevant when an untrusted or compromised NVMe device or NVMe/TCP target can observe discard payloads and when local conditions can force the fallback page path.
5. One-sentence report phrase
An uninitialized discard fallback page in the NVMe host path can leak stale kernel memory bytes to an NVMe controller or NVMe/TCP target under memory pressure, but no UAF, memory corruption, integrity impact, availability impact, or direct remote trigger is established.
6. Manual review recommendation
MANUAL CHECK RECOMMENDED
Manual review is recommended to determine whether the affected deployment uses NVMe/TCP or untrusted NVMe devices and whether local users can realistically trigger discard operations plus memory pressure. It is not a strong Important candidate from the supplied evidence.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: nvme: zero the discard fallback page
Commit: dc4d4b70a863f7e39ef8bd137634be4e6db8b084
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=dc4d4b70a863f7e39ef8bd137634be4e6db8b084
Commit description:
nvme_setup_discard() always maps sizeof(struct nvme_dsm_range) *
NVME_DSM_MAX_RANGES = 4096 bytes as the DSM payload however many ranges
the command declares, because some devices ignore the 'Number of Ranges'
field - the Fixes: commit records two that read past the declared ranges.
A single-range discard fills only the first 16 bytes.
Normally the buffer comes from kzalloc() and the other 4080 bytes are
zero. When that allocation fails the code falls back to the
per-controller ctrl->discard_page, which nvme_init_ctrl() obtains with
alloc_page(GFP_KERNEL) and nothing ever zeroes, so those 4080 bytes are
whatever the page last held and are handed to the controller. Reaching
it requires the kzalloc(GFP_ATOMIC | __GFP_NOWARN) to fail, that is
memory pressure; it is not remotely triggerable. Failing the allocation
under KMSAN reproduces it, with the leaked tail full of vmemmap struct
page pointers. The extent in the report is a partial transfer of the
payload, not the whole 4096 bytes; the 16-byte boundary in it is the one
declared range:
[ 11.991601] BUG: KMSAN: uninit-value in dma_map_phys+0x14c8/0x1900
[ 11.991969] dma_map_phys+0x14c8/0x1900
[ 11.992220] dma_map_page_attrs+0xcf/0x130
[ 11.992485] e1000_xmit_frame+0x4099/0x6d10
[ 11.992768] dev_hard_start_xmit+0x22f/0xa80
[ 11.993068] sch_direct_xmit+0x35c/0xcb0
[ 11.993315] __dev_queue_xmit+0x1ee5/0x5eb0
[ 11.993608] ip_finish_output2+0x1903/0x1c30
[ 11.993881] ip_finish_output+0x288/0x870
[ 11.994125] ip_output+0x15e/0x400
[ 11.994365] __ip_queue_xmit+0x1e85/0x1fb0
[ 11.994639] ip_queue_xmit+0x60/0x80
[ 11.994899] __tcp_transmit_skb+0x4e71/0x5fa0
[ 11.995210] tcp_write_xmit+0x3a36/0x9160
[ 11.995533] __tcp_push_pending_frames+0xc5/0x3c0
[ 11.995854] tcp_push+0x7dc/0x840
[ 11.996076] tcp_sendmsg_locked+0x766c/0x8400
[ 11.996371] tcp_sendmsg+0x4b/0x90
[ 11.996572] inet_sendmsg+0x134/0x2a0
[ 11.996823] __sock_sendmsg+0x265/0x360
[ 11.997076] sock_sendmsg+0x100/0x1e0
[ 11.997293] nvme_tcp_try_send+0x196f/0x6370
[ 11.997605] nvme_tcp_queue_rq+0x1d54/0x20b0
[ 11.997882] blk_mq_dispatch_rq_list+0x5ee/0x2e50
[ 11.998175] __blk_mq_sched_dispatch_requests+0x16dc/0x24a0
[ 11.998539] blk_mq_sched_dispatch_requests+0x11b/0x2c0
[ 11.998865] blk_mq_run_work_fn+0x13b/0x280
[ 11.999146] process_scheduled_works+0x966/0x1ad0
[ 11.999465] worker_thread+0xe44/0x1480
[ 11.999709] kthread+0x53b/0x600
[ 11.999927] ret_from_fork+0x29f/0x7c0
[ 12.000191] ret_from_fork_asm+0x1a/0x30
[ 12.000460]
[ 12.000558] Uninit was created at:
[ 12.000788] __alloc_frozen_pages_noprof+0x8bf/0xd30
[ 12.001096] alloc_pages_mpol+0x1d0/0x5f0
[ 12.001326] alloc_pages_noprof+0x102/0x290
[ 12.001627] nvme_init_ctrl+0x5a3/0x9f0
[ 12.001891] nvme_tcp_create_ctrl+0xd75/0x19b0
[ 12.002170] nvmf_dev_write+0x4c68/0x4fd0
[ 12.002426] vfs_write+0x587/0x1a10
[ 12.002636] __x64_sys_write+0x207/0x4f0
[ 12.002874] x64_sys_call+0x2ff0/0x3ea0
[ 12.003123] do_syscall_64+0x147/0x3b0
[ 12.003400] entry_SYSCALL_64_after_hwframe+0x77/0x7f
[ 12.003680]
[ 12.003777] Bytes 16-2843 of 2844 are uninitialized
[ 12.004068] Memory access of size 2844 starts at ffff888109f82000
[ 12.004412]
[ 12.004530] CPU: 0 UID: 0 PID: 101 Comm: kworker/0:1H Not tainted 7.2.0-rc5-NVMECTL-gf5098b6bae76 #1 PREEMPT(lazy)
[ 12.005127] Hardware name: QEMU Ubuntu 24.04 PC v2 (i440FX + PIIX, arch_caps fix, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
[ 12.005762] Workqueue: kblockd blk_mq_run_work_fn
[ 12.006073] =====================================================
Allocate the page with __GFP_ZERO. The single allocation site covers
every use of it: bytes no discard has written stay zero, and bytes one
did write hold that controller's own range list, which it has already
been sent.
Fixes: 530436c ("nvme: Discard workaround for non-conformant devices")
Cc: [email protected]
Signed-off-by: Yehyeong Lee <[email protected]>
[Commit description truncated; see the upstream URL below]
Changed files:
drivers/nvme/host/core.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=dc4d4b70a863f7e39ef8bd137634be4e6db8b084
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-89483 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89483
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:H/PR:L/UI:N/S:U/C:L/I:N/A:N
The Best / paranoid CVSS vector: AV:A/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N
The Best / paranoid CVSS score: 4.8
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: 2
Paranoid ActionableScore: 3
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 REGULAR
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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