* [CVE-2026-99063][LOW] dm ioctl: don't let data_start run past the buffer
@ 2026-10-26 18:33 21% AL-KERNEL
0 siblings, 0 replies; 1+ results
From: AL-KERNEL @ 2026-10-26 18:33 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-99063
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: dm ioctl: don't let data_start run past the buffer
Commit: 98195e822343a656b92e235847ab3e72b1a3f920
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=98195e822343a656b92e235847ab3e72b1a3f920
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99063
Analysis date: Mon, 26 Oct 2026 14:33:14 -0400
ActionableScore: 0
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO
Summary:
A host-privileged device-mapper ioctl can disclose seven bytes past a minimally sized heap buffer through an oversized result copy.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-99063 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99063
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: LOW
Manual review required: NO
A detailed explanation of the methodology and priority rules is included
at the end of this message.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2026-99063 LOW https://www.kernelcve.org/list/?q=CVE-2026-99063 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE AEGIS_AS=0 LEGACY=LOW RESULT=DIFF (final Legacy and Aegis differ; FINAL: LOW, Aegis: MODERATE) Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:H/UI:N/S:U/C:L/I:N/A:L';CWE-125;*CWE-200;*CWE-20;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:L/I:N/A:N';BEST CVSS score: '3.4';DESCR 'An out-of-bounds kernel heap read occurs because get_result_buffer can set data_start to the aligned end of struct dm_ioctl even when the userspace buffer ends seven bytes earlier at offsetof struct dm_ioctl data. A DM_LIST_DEVICES request with data_size 305 can make ctl_ioctl copy 312 bytes from a 305 byte allocation and disclose seven adjacent slab bytes. For the CVSS the PR:H value is selected because reliable direct triggering requires root or equivalent CAP_SYS_ADMIN access to device mapper control ioctls. The demonstrated primitive is a small information disclosure with no supported out-of-bounds write or UAF path and it is not directly network reachable. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 3.4 and the production ActionableScore returned 0 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were final reconciliation stage LOW to LOW because KP specialist did not establish a qualifying panic and the cross model evidence reconciliation rule was applied. The legacy KP specialist has no review artifact for this run. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were KPANIC_UNSUPPORTED_REMOVED and V64_AEGIS_UNSUPPORTED_PROMOTION_BLOCKED. The independent weaker Aegis shadow evaluated CVSS 2.1 and ActionableScore 0 with primitive class CLASS_C and manual review REQUIRED. Its independently reconciled impact was MODERATE. The models disagreed but the aggregation rules retained the production result. The final reported impact is LOW.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 0) MAYBE READ KASAN OOB DISK LEAK LINUS SYZBOT KPANIC_UNSUPPORTED_REMOVED V64_AEGIS_UNSUPPORTED_PROMOTION_BLOCKED - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=0
PrimitiveClass=CLASS_B
RealUAF=NO
HostAdminRequired=YES
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
RequiresHostUID0=NO
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO
1. ActionableScore
* Raw base score: 0 (+1 bounded heap OOB read, +1 confirmed disclosure, -2 proven host-administrator-equivalent privilege).
* Conservative score: 0. No floor or cap applies.
* Raw paranoid score: 0.
* Paranoid score: 0. No technically supported stronger effect.
* Final recommended bucket: **Ordinary Moderate**::
2. Signal breakdown
* +1 weak read-only OOB primitive: `data_start` can point seven bytes beyond the 305-byte allocation, causing `_copy_to_user()` to read 312 bytes.
* +1 confidentiality plausible: seven adjacent slab bytes are copied to userspace, so this is a concrete small kernel-memory disclosure.
* -2 full host-admin-equivalent privilege: supplied evidence states device-mapper control ioctls require root or equivalent host `CAP_SYS_ADMIN`.
* No OOB write, UAF, active-state corruption, retry-accumulated B5-R chain, arbitrary read, or attacker-selected target is shown.
* No crash point: the KASAN report diagnoses the invalid read; it does not establish a production host crash.
* No authorization bypass exists; the patch clamps a length/offset rather than restoring a missing security guard.
* NEW52/B5-R does not apply because this is a fixed seven-byte OOB read, not an accumulated write whose corrupted state is later consumed.
3. Reachability analysis
The trigger is `DM_LIST_DEVICES` with minimum `data_size`. The complete path is local and requires device-mapper control authority, positively described as root or equivalent host `CAP_SYS_ADMIN`. Numeric host UID 0 is not strictly required because an equivalent capability suffices. No attacker-obtainable user-namespace capability path, remote path, special hardware, prior delegated setup, or timing race is shown.
4. Primitive and severity reading
The exact primitive is a bounded seven-byte heap over-read disclosed through `copy_to_user`. It is CLASS_B as a real but narrowly constrained kernel disclosure, with no memory write or lifetime violation. The shown effect is disclosure of adjacent slab bytes; LPE, broader arbitrary disclosure, integrity impact, and reliable denial of service are unsupported. Host-admin-only triggering makes this unsuitable as an Important candidate and permits downgrade.
5. One-sentence report phrase
A host-privileged device-mapper ioctl can disclose seven bytes past a minimally sized heap buffer through an oversized result copy.
6. Manual review advice
MANUAL CHECK RECOMMENDED
Confirm that the product does not delegate device-mapper control authority below host-administrator equivalence.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: dm ioctl: don't let data_start run past the buffer
Commit: 98195e822343a656b92e235847ab3e72b1a3f920
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=98195e822343a656b92e235847ab3e72b1a3f920
Commit description:
struct dm_ioctl has seven bytes of trailing padding, so the smallest
buffer userspace is allowed to ask for, offsetof(struct dm_ioctl, data),
is seven bytes shorter than sizeof(struct dm_ioctl).
get_result_buffer() sets data_start to sizeof(struct dm_ioctl) without
looking at how big the buffer actually is. Ask for the minimum and
data_start ends up seven bytes past the end. Callers add it to
data_size, and ctl_ioctl() copies that much back to userspace:
BUG: KASAN: slab-out-of-bounds in _copy_to_user+0xad/0xd0
Read of size 312 at addr ffff8880169e4c00 by task repro-dm/140
ctl_ioctl+0x5e3/0xcb0
dm_ctl_ioctl+0x25/0x40
allocated 305-byte region [ffff8880169e4c00, ffff8880169e4d31)
A DM_LIST_DEVICES with data_size set to 305 is enough to hit it, and the
seven bytes that leak are whatever sat next to the allocation.
Clamp data_start to the buffer size.
Note that this is not a security bug because the out-of-bounds read can
only be triggered by root.
Reported-by: [email protected]
Closes: https://syzkaller.appspot.com/bug?extid=48d935cf48a4a76be346
Fixes: 76c072b ("dm ioctl: move compat code")
Cc: [email protected]
Signed-off-by: Palla Raghunath <[email protected]>
Signed-off-by: Mikulas Patocka <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
drivers/md/dm-ioctl.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=98195e822343a656b92e235847ab3e72b1a3f920
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-99063 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99063
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:N/A:N
The Best / paranoid CVSS vector: AV:L/AC:L/PR:H/UI:N/S:U/C:L/I:N/A:L
The Best / paranoid CVSS score: 3.4
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: 0
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: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW
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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