* [CVE-2026-98725][IMPORTANT] nvmet-auth: fix out-of-bounds write in nvmet_auth_challenge()
@ 2026-10-24 15:33 21% AL-KERNEL
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From: AL-KERNEL @ 2026-10-24 15:33 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-98725
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: NO
Patch: nvmet-auth: fix out-of-bounds write in nvmet_auth_challenge()
Commit: 9d61131acd742cf97ee64e453383e41b46568513
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9d61131acd742cf97ee64e453383e41b46568513
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98725
Analysis date: Sat, 24 Oct 2026 11:33:46 -0400
ActionableScore: 5
ActionableScore lower bound: unknown
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES
Summary:
An unauthenticated NVMe/TCP initiator can supply a short AUTH_RECEIVE length that triggers a confirmed heap OOB challenge write and kernel panic.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98725 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98725
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: IMPORTANT
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-2026-98725 IMPORTANT https://www.kernelcve.org/list/?q=CVE-2026-98725 CHECK WITH IMPACT FROM ORIG NN IMPORTANT | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=3 LEGACY=IMPORTANT RESULT=DIFF INDEPENDENT_LEGACY=IMPORTANT INDEPENDENT_RESULT=DIFF TEMP_KPANIC_MERGE=IMPORTANT_WINS_DISAGREEMENT PRE_MERGE_LEGACY=IMPORTANT (final Legacy and Aegis differ; FINAL: IMPORTANT, Aegis: MODERATE_KPANIC) 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-131;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 incorrect size calculation in nvmet_auth_challenge uses sizeof on a dereferenced void pointer and counts only one byte for the fixed challenge header. A short AUTH_RECEIVE buffer can therefore pass validation before a 32 byte challenge write crosses the end of its slab allocation. The demonstrated result is a KASAN detected kernel panic, while the concrete heap out of bounds write also creates a plausible but unproven path to adjacent object corruption and privilege escalation. For the CVSS the PR:N value is selected because an initiator that can reach the configured NVMe Fabrics target appears able to trigger the flaw while authentication is still in progress and does not need prior authentication. AV:A reflects the usual requirement for access to the local or isolated NVMe storage network. Automated impact decision path. The original SimpleNet classifier selected IMPORTANT. The primary LLM estimated paranoid CVSS 8.8 and the production ActionableScore returned 5 with recommendation Actionable Moderate / Strong Important candidate requiring manual review. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were KP and FD specialist checks stage IMPORTANT to IMPORTANT because a specific evidence based protection or manual review veto was applied. The legacy KP specialist has no review artifact for this run. The legacy FD or DH downgrade specialist produced a review artifact and its decision was processed by the applicable downgrade and preservation rules. Exact triggered rule markers were V42_LEGACY_CLASSA_FD_VETO and MANUAL_REVIEW_REQUIRED and TEMP_KPANIC_MERGE_IMPORTANT_WINS. The independent weaker Aegis shadow evaluated CVSS 4.3 and ActionableScore 3 with primitive class CLASS_B and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. Cross model aggregation changed the production result under an enabled evidence gated merge rule. The final reported impact is IMPORTANT.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5) MAYBE WRITE KASAN OOB NVME LINUS V42_LEGACY_CLASSA_FD_VETO MANUAL_REVIEW_REQUIRED TEMP_KPANIC_MERGE_IMPORTANT_WINS - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=5
PrimitiveClass=CLASS_A
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
RequiresHostUID0=NO
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO
1. ActionableScore
* Raw base score: 5.
* Conservative score: 5; no floor or cap applied.
* Raw paranoid score: 5.
* Paranoid score: 5; stronger consequences require unsupported adjacent-object evidence.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::
2. Signal breakdown
* +2 — Strong corruption primitive: attacker-selected short AUTH_RECEIVE length passes an undercounted check, followed by a confirmed slab OOB write. KASAN shows a 32-byte write starting 16 bytes into a 33-byte allocation.
* +2 — Network reachability: an unauthenticated initiator can send the malformed command to a configured NVMe/TCP target.
* +1 — Reliable kernel crash/strong DoS: KASAN detected the overwrite and the supplied trace demonstrates panic with `panic_on_warn`.
* No separate integrity, weak-LPE, or memory-layout point: these would duplicate the OOB primitive without a named corrupted object.
* No confidentiality, arbitrary write, controlled payload, controlled adjacent target, reclaim, or LPE is shown.
* B5-R does not apply: no retry-accumulated index or re-entry mechanism exists.
* B4-PENDING does not apply: this is a size-validation failure, not a DENY-to-ALLOW authorization decision.
3. Reachability analysis
The supported attacker is a network initiator able to reach an already configured NVMe/TCP target. Authentication need not have completed, so effective host-administrator privilege or host UID 0 is not required. Target provisioning is prior administrative setup, but the subsequent malformed AUTH_RECEIVE trigger is remote and unprivileged. No namespace capability, special hardware, or race is required.
4. Primitive and severity reading
The exact primitive is a bounded but concrete heap/slab OOB write caused by `sizeof(*d)` evaluating to one for a `void *`, undercounting the fixed header by 15 bytes. This is CLASS_A attacker-influenced kernel corruption, not a UAF. Kernel panic is demonstrated; corruption of a useful adjacent object is plausible but unproven. ImportantCandidate is retained because a real remotely reachable heap overwrite warrants exploit-leverage review. Auto-downgrade is unsafe despite the generated, non-arbitrary payload.
5. One-sentence report phrase
An unauthenticated NVMe/TCP initiator can supply a short AUTH_RECEIVE length that triggers a confirmed heap OOB challenge write and kernel panic.
6. Manual review advice
MANUAL CHECK REQUIRED
Determine allocator adjacency and whether the fixed challenge bytes can corrupt a useful neighboring slab object.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: nvmet-auth: fix out-of-bounds write in nvmet_auth_challenge()
Commit: 9d61131acd742cf97ee64e453383e41b46568513
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9d61131acd742cf97ee64e453383e41b46568513
Commit description:
nvmet_auth_challenge() receives its output buffer as a void pointer.
sizeof(*d) therefore evaluates to one with GCC and undercounts the fixed
challenge header by 15 bytes. A short AUTH_RECEIVE buffer can pass the
check before the challenge is copied past the end of its allocation.
Use the typed challenge pointer when calculating the response size.
BUG: KASAN: slab-out-of-bounds in nvmet_execute_auth_receive (drivers/nvme/target/fabrics-cmd-auth.c:442 drivers/nvme/target/fabrics-cmd-auth.c:569)
Write of size 32 by task kworker/1:1H/64
Workqueue: nvmet_tcp_wq nvmet_tcp_io_work
Call Trace:
nvmet_execute_auth_receive (drivers/nvme/target/fabrics-cmd-auth.c:442 drivers/nvme/target/fabrics-cmd-auth.c:569)
nvmet_tcp_try_recv_pdu (drivers/nvme/target/tcp.c:1119 drivers/nvme/target/tcp.c:1243)
nvmet_tcp_io_work (drivers/nvme/target/tcp.c:1350 drivers/nvme/target/tcp.c:1382 drivers/nvme/target/tcp.c:1445)
process_one_work (kernel/workqueue.c:3322)
worker_thread (kernel/workqueue.c:3405 kernel/workqueue.c:3486)
kthread (kernel/kthread.c:436)
ret_from_fork (arch/x86/kernel/process.c:158)
ret_from_fork_asm (arch/x86/entry/entry_64.S:245)
The buggy address is located 16 bytes inside of
allocated 33-byte region [ffff888000554e80, ffff888000554ea1)
Kernel panic - not syncing: KASAN: panic_on_warn set ...
Cc: [email protected]
Fixes: db1312d ("nvmet: implement basic In-Band Authentication")
Reported-by: [email protected]
Closes: https://lore.kernel.org/all/[email protected]/
Assisted-by: Codex:gpt-5.6
Reviewed-by: Christoph Hellwig <[email protected]>
Reviewed-by: Hannes Reinecke <[email protected]>
Signed-off-by: Weiming Shi <[email protected]>
Signed-off-by: Keith Busch <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
drivers/nvme/target/fabrics-cmd-auth.c
drivers/nvme/target/tcp.c
kernel/workqueue.c
kernel/kthread.c
arch/x86/kernel/process.c
arch/x86/entry/entry_64.S
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=9d61131acd742cf97ee64e453383e41b46568513
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98725 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98725
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: unknown
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: IMPORTANT
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): IMPORTANT
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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