[CVE-2026-90333][IMPORTANT] dm-integrity: replace forgeable discard filler with a keyed sector marker [ Upstream

[AL-KERNEL <alkernel@kernelcve.org>]

CVE: CVE-2026-90333
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: dm-integrity: replace forgeable discard filler with a keyed sector marker [ Upstream
Commit: 5c58ea19a909ef6bed4f0f824e9cd7e30d7e4775
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5c58ea19a909ef6bed4f0f824e9cd7e30d7e4775
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90333
Analysis date: Thu, 17 Sep 2026 15:20:17 -0400
ActionableScore: 6
ActionableScore lower bound: 5
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-90333 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90333

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.

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AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-90333	IMPORTANT	https://www.kernelcve.org/list/?q=CVE-2026-90333 CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:H';CWE-345;CWE-347;CWE-354;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:H/A:L';BEST CVSS score: '7.1';DESCR 'dm-integrity accepted a constant DISCARD_FILLER tag as evidence that a block was discarded and then skipped HMAC verification for that block. An attacker with raw write access to the backing device but without the integrity key could stamp a chosen metadata tag with all 0xf6 bytes and make modified storage content be treated as authentic. For the CVSS the PR:L is used in the paranoid score because the attacker does not need the integrity key but does need practical write access to the lower raw device or an equivalent storage layer position. The issue is not directly network reachable through dm-integrity itself. Impact is an integrity bypass for protected block data, with possible availability impact if trusted data is corrupted or system data is modified.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 6)	YES	DISK INIT LOG HARDWARE LINUS KPANIC MEMORY  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS	NO	NO	checked

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

ActionableScore=6
ActionableScoreLower=5
PrimitiveClass=CLASS_A
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO

1. ActionableScore

* Raw conservative score: 5
* Conservative score: 5. No floor or cap applied.
* Raw paranoid score: 6
* Paranoid score: 6. No floor or cap applied.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

2. Signal breakdown

Positive conservative signals:

* +2 Security-boundary bypass: dm-integrity treats a constant all 0xf6 DISCARD_FILLER tag as proof of discard state and skips HMAC verification.
* +1 Integrity plausible: attacker-controlled block metadata can make modified backing storage content be accepted as authentic without the integrity key.
* +1 Practical exploit chain strongly implied: raw backing-device write -> forged discard tag -> HMAC bypass -> unauthenticated data served through dm-integrity.
* +1 Important storage integrity path: dm-integrity is specifically a block-layer integrity/authentication mechanism, so bypassing tag validation affects a security-relevant storage boundary.

Additional paranoid signal:

* +1 Availability plausible: forged authenticated-looking storage content can corrupt trusted data or system data, which may cause device, filesystem, or workload unavailability.

Non-awarded or withheld signals:

* +0 RealUAF: no UAF, stale pointer, double free, refcount mutation, or lifetime corruption is established.
* +0 Memory corruption: this is a cryptographic/authentication logic bypass, not kernel memory corruption.
* +0 Remote reachable: no direct network path through dm-integrity is established.
* +0 Local unprivileged trigger: ordinary local user reachability is not established.
* +0 Confidentiality: the patch supports integrity bypass, not a read/disclosure primitive.
* +0 Strong LPE: no privilege escalation, arbitrary write to kernel memory, credential manipulation, or controlled kernel corruption is shown.
* +0 Host-admin penalty: raw backing-device write access is required, but host-admin-equivalent privilege is not positively established by the supplied evidence.
* +0 Rare subsystem penalty: dm-integrity and allow_discards are configuration dependent, but the prompt requires concrete evidence before subtracting for rarity.

3. Reachability analysis

The attacker must have raw write access to the backing device or an equivalent lower storage-layer position, but must not know the dm-integrity HMAC key. This is not ordinary packet-triggered or syscall-only reachability. It is also not shown to be reachable by an unprivileged local user.

HostAdminRequired is UNKNOWN because raw backing-device write access often implies high local privilege in ordinary host deployments, but the supplied attacker model can also represent a compromised lower storage layer, storage service, device passthrough, or another actor below the integrity layer. NamespaceScopedPrivilege is NO because the relevant operation is not a namespace-scoped capability path. Prior setup exists in the sense that the dm-integrity target must be configured with the old allow_discards behavior in standalone/internal-hash mode. No special hardware or race is required.

4. Primitive and severity interpretation

The primitive is a cryptographic integrity/authentication bypass in dm-integrity discard-tag handling. A stored all 0xf6 tag is semantically reinterpreted as an authentic discarded-block marker, and dm_integrity_rw_tag() skips HMAC verification for that block. This lets an attacker who can write raw backing metadata forge the marker without the key.

PrimitiveClass is CLASS_A because the bug defeats a meaningful security boundary: authenticated block integrity. The demonstrated consequence is unauthorized integrity modification of protected block data. The speculative consequence is broader availability impact if critical data is corrupted. ImportantCandidate is YES because this is not a DoS-only bug and not a simple configuration warning. AutoDowngradeAllowed is NO because automatically closing it as ordinary Moderate would lose a concrete storage integrity boundary bypass.

Likely operational severity is actionable Moderate at minimum, with Strong Important review warranted depending on deployment exposure of the backing device and the sensitivity of data protected by dm-integrity.

5. One-sentence report phrase

dm-integrity allowed a forgeable constant discard tag to bypass HMAC verification, so an attacker with raw backing-device write access but without the integrity key could make modified storage blocks appear authentic.

6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is a concrete cryptographic storage-integrity boundary bypass with high integrity impact, and deployment-specific exposure of raw backing-device write access determines whether it should be treated as Important.

7. Call-site confidence

Call-site confidence: high

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

Patch: dm-integrity: replace forgeable discard filler with a keyed sector marker [ Upstream
Commit: 5c58ea19a909ef6bed4f0f824e9cd7e30d7e4775
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5c58ea19a909ef6bed4f0f824e9cd7e30d7e4775

Changed files:
  drivers/md/dm-integrity.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=5c58ea19a909ef6bed4f0f824e9cd7e30d7e4775

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

The original Linux kernel CVE announcement for CVE-2026-90333 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90333

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:L/PR:H/UI:N/S:U/C:N/I:H/A:L
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:H
  The Best / paranoid CVSS score: 7.1

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: 5
  Paranoid ActionableScore: 6

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