* [CVE-2026-89575][MODERATE 7.0] dm raid1: reserve space for NUL-terminator in build_constructor_string()
@ 2026-09-12 9:14 21% AL-KERNEL
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From: AL-KERNEL @ 2026-09-12 9:14 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-89575
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: dm raid1: reserve space for NUL-terminator in build_constructor_string()
Commit: 0a3657ebd6b517b60cdc5123894047616974e25b
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0a3657ebd6b517b60cdc5123894047616974e25b
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89575
Analysis date: Sat, 12 Sep 2026 05:14:37 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES
Summary:
No one-sentence report phrase was found.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-89575 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89575
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-2026-89575 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-89575 CHECK WITH IMPACT FROM ORIG NN MODERATE Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';CWE-131;*CWE-787;CWE-120;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A one byte NUL heap overflow can occur in dm raid1 userspace log construction because build_constructor_string() reserves space for the maximum 20 decimal digits of a long long value but does not reserve space for the terminating NUL written by sprintf(). A local actor able to create or reload the affected Device Mapper raid1 target can trigger an out of bounds write in kernel memory when the formatted value reaches the maximum digit length. For the CVSS the PR:L is used for the paranoid score because some deployments may delegate storage mapping control to a reduced capability root, container root, or storage management service account rather than a full host administrator. The issue is not network reachable and is triggered through local Device Mapper control plane operations. Impact is at least local denial of service via kernel crash and in worst case may allow confidentiality or integrity impact due to kernel heap memory corruption.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5) SKIP CVE-2026-89575 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: f5db4af466e2 YES NO NO unknown MAYBE OOB DISK SIMPLEFIX LINUS KPANIC - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=5
ActionableScoreLower=4
PrimitiveClass=CLASS_B
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
1. ActionableScore
* Raw conservative score: 4
* Conservative score: 4. No floor or cap applied.
* Raw paranoid score: 5
* Paranoid score: 5. No floor or cap applied.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::
2. Signal breakdown
Positive conservative signals:
* +2. Concrete kernel heap out of bounds write. The allocation reserves space for up to 20 decimal digits but not for the terminating NUL written by sprintf().
* +1. Realistic kernel crash or memory corruption consequence. A one byte heap overflow in kernel memory can corrupt the adjacent allocation or allocator state, even though no arbitrary write is demonstrated.
* +1. Important storage path. The bug is in Device Mapper raid1 userspace log construction, which belongs to storage mapping/control infrastructure.
Positive paranoid signal:
* +1. Weak exploitation concern. The primitive is a real kernel heap overwrite, and the attacker may influence the constructor string size and Device Mapper table parameters, but the payload is constrained to a single NUL byte and no controlled target is shown.
Non-awarded signals:
* Controlled reclaim not demonstrated.
* Arbitrary or directed kernel write not demonstrated.
* RealUAF not established.
* Concrete repeated release/refcount mutation not present.
* Confidentiality and integrity are not scored as established consequences because no disclosure path, arbitrary write, credential manipulation, or protected object overwrite is shown.
* Remote reachability not established.
* Extra Availability not awarded because the crash/corruption consequence is already counted once.
* CLASS_A not used because the overwrite is constrained to one NUL byte and no strong exploitation primitive is established.
Negative signals:
* No host-admin penalty was applied because the supplied patch text does not show the complete Device Mapper privilege boundary. Device Mapper table creation is generally administrative in normal deployments, but the prompt requires positive evidence for HostAdminRequired=YES and for a -2 penalty in this triage output.
3. Reachability analysis
The vulnerable path is reached when constructing a dm raid1 userspace log target string. A practical trigger would require the ability to create or reload the affected Device Mapper target with parameters that make the formatted numeric value consume the maximum 20 decimal digits.
This is a local control-plane path, not a packet-processing or remote network path. Ordinary network traffic cannot directly reach build_constructor_string().
In typical Linux deployments, Device Mapper target creation and reload are administrative operations through dmsetup or the DM ioctl interface. However, the supplied evidence does not include the exact capability check or namespace boundary for the complete trigger chain, so HostAdminRequired is kept as UNKNOWN rather than YES. NamespaceScopedPrivilege is also UNKNOWN because no evidence shows that the complete Device Mapper operation is available inside attacker-created namespaces.
No race is involved. No special hardware requirement is established.
4. Primitive and severity interpretation
The exact primitive is an off-by-one kernel heap overwrite caused by missing allocation space for the sprintf() terminating NUL byte. This is not a UAF and not a repeated lifetime/refcount mutation.
The overwrite is constrained because the written byte is the NUL terminator, and the patch does not show attacker selection of the adjacent heap target or a controlled replacement object. This keeps the primitive in CLASS_B rather than CLASS_A.
The demonstrated consequence is kernel memory corruption with plausible crash/DoS. The speculative consequence is possible privilege escalation or broader C/I impact if the one byte NUL overwrite can be shaped against a useful adjacent object, but that exploitation path is not established by the patch.
ImportantCandidate is YES because a concrete kernel heap out of bounds write exists and exploitability is not safely dismissible from the small patch alone. AutoDowngradeAllowed is NO because automatic closure would risk losing a real kernel memory corruption primitive that needs manual review.
Likely operational severity is Actionable Moderate, with Strong Important candidacy depending on whether manual analysis finds a practical way to place or influence the adjacent object.
5. One-sentence report phrase
A one byte NUL heap overflow in dm raid1 userspace log construction can occur because build_constructor_string() reserves space for the maximum decimal digits but not for the terminating NUL written by sprintf(), creating a local kernel memory corruption primitive that requires manual review.
6. Manual review recommendation
MANUAL CHECK REQUIRED
Reason: the patch fixes an explicit kernel heap out of bounds write, and even though the overwrite is constrained to one NUL byte, the exploitability and adjacent object impact require manual kernel memory corruption review.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: dm raid1: reserve space for NUL-terminator in build_constructor_string()
Commit: 0a3657ebd6b517b60cdc5123894047616974e25b
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0a3657ebd6b517b60cdc5123894047616974e25b
Commit description:
Reserve space for the termination NUL after the maximum 20 decimal
digits of a long long value to avoid buffer overflow in sprintf().
Fixes: f5db4af ("dm raid1: add userspace log")
Cc: [email protected]
Signed-off-by: Ilya Krutskih <[email protected]>
Signed-off-by: Mikulas Patocka <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
drivers/md/dm-log-userspace-base.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=0a3657ebd6b517b60cdc5123894047616974e25b
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-89575 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89575
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:L/I:L/A:H
The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
The Best / paranoid CVSS score: 7
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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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