* [CVE-2026-98750][MODERATE 7.0] tty: fix saved termios reset race [ Upstream
@ 2026-10-19 9:11 21% AL-KERNEL
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From: AL-KERNEL @ 2026-10-19 9:11 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-98750
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: tty: fix saved termios reset race [ Upstream
Commit: 1572d86bcf0bcb848d20fc5e5de7ed6963034c2b
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1572d86bcf0bcb848d20fc5e5de7ed6963034c2b
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98750
Analysis date: Mon, 19 Oct 2026 05:11:59 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES
Summary:
A race between TTY close and device re-registration can free saved termios storage while it is still being updated, producing a heap use-after-free with kernel-crash impact and unresolved post-free write leverage.
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ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98750 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98750
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-2026-98750 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-98750 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=4 LEGACY=MODERATE_KPANIC RESULT=SAME (final reconciliation agrees; DECISION: both MODERATE_KPANIC) 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-416;CWE-362;*CWE-664;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A race between closing an existing TTY and registering another device with the same minor number can cause saved termios memory to be freed while the close path is still using or updating it. The resulting use after free can cause memory corruption or a kernel crash when device registration overlaps with termios preservation for the old TTY instance. For the CVSS the PR:L value is used because a local user must be able to access and close the affected TTY while device re-registration or minor reuse occurs. AC:H applies because successful triggering depends on a narrow timing window and on a driver that does not guarantee that the reused minor is no longer active. The issue is not directly network reachable. Impact is at least a local denial of service via kernel crash and in the worst case may allow confidentiality or integrity impact and local privilege escalation through reuse of freed kernel memory. Automated impact decision path. The original SimpleNet classifier selected MODERATE_KPANIC. The primary LLM estimated paranoid CVSS 7 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 CVSS and initial triage stage MODERATE_KPANIC to IMPORTANT because the CVSS score, vector or bug class threshold rule was applied. KP and FD specialist checks stage IMPORTANT to MODERATE_KPANIC because KP specialist did not establish a qualifying panic. The legacy KP specialist produced a review artifact and its decision was processed by the applicable KP rules. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were INCREASED_TO_HIGH_BASED_ON_GUESSCVSS and DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFKP. The independent weaker Aegis shadow evaluated CVSS 2.5 and ActionableScore 4 with primitive class CLASS_B and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. The shadow agreed with the final production impact and aggregation did not change that impact. The final reported impact is MODERATE_KPANIC.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5) MAYBE RACE UAF HARDWARE LINUS KPANIC KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFKP - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=5
ActionableScoreLower=4
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO
1. ActionableScore
* Raw conservative score: 2
* Conservative score: 4
* Raw paranoid score: 3
* Paranoid score: 5
* Conservative floor applied: 2 -> 4 under the real UAF floor.
* Paranoid floor applied: 3 -> 5 because the stale operation can write saved termios state into freed heap storage rather than only dereference it and fault.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::
2. Signal breakdown
Conservative signals:
* +2 Real UAF. Device registration can free `driver->termios[index]` while the TTY close path is still saving state through the same allocation.
* +1 Realistic kernel crash or strong DoS. A close-path access to freed heap storage can cause an Oops or allocator-state corruption.
* -1 Hard timing condition. Closing the old TTY must overlap reuse and registration of the same minor number.
Paranoid signal:
* +1 Structured stale-object leverage. Saving termios is a write to structured heap state, and the saved settings may be influenced through normal TTY configuration before close. If the allocation has been reused, the stale write can affect replacement storage.
Not awarded:
* No controlled reclaim or chosen replacement object is demonstrated.
* No arbitrary or directed kernel write is demonstrated.
* No confidentiality, protected-state integrity, or LPE point is awarded merely from possible allocator reuse.
* No local-unprivileged bonus is awarded because control of the complete close plus re-registration sequence is unresolved.
* No remote-reachability signal applies.
* No extra availability point is awarded for the same possible kernel crash.
* No repeated release or refcount signal applies. The bug is a free-versus-concurrent-use race, not a second `put`, `free`, or refcount mutation on the same reference.
* B3-PENDING, B4-PENDING, B5-R, and the checksum trust-boundary profiles do not apply.
3. Reachability analysis
A process with permission to open and configure the affected TTY can influence its termios state and execute the close path. The other side of the race is registration of another device using the same driver minor number.
The supplied evidence does not establish whether an ordinary user can independently force the required re-registration. Depending on the driver, it may require device hotplug, a driver event, physical interaction, or administrative device management. Therefore the complete below-host-admin trigger is unresolved and `HostAdminRequired=UNKNOWN`.
TTY minor reuse is not a user-namespace or network-namespace capability operation, so `NamespaceScopedPrivilege=NO`. No remote packet path exists. The timing window is narrow because freeing during registration must overlap saving termios during close, although repeated attempts may be possible when the relevant device lifecycle is controllable.
4. Primitive and severity interpretation
The exact primitive is a heap use-after-free with a potentially stale write. Registration reads the saved termios pointer, clears the array slot, and frees the allocation. A concurrent close operation may still be saving termios through that allocation.
The object is structured saved TTY state rather than a fixed DMA buffer. The stale use performs an update, not merely a shallow stale read or guaranteed immediate fault. This supports `CLASS_B`, but not `CLASS_A`, because controlled reclaim, selected destination, arbitrary payload, callback influence, and privilege escalation are not established.
There is no concrete repeated release or refcount operation. The first operation is `kfree`, while the concurrent operation uses or updates the allocation rather than freeing it again.
The demonstrated consequence is a real lifetime violation with plausible kernel crash and heap corruption. A useful write into reclaimed storage is technically plausible, but a controllable replacement object and security-sensitive victim are unresolved. This unresolved post-free write surface makes the issue an Important candidate for review and prevents automatic downgrade, without proving Important severity or LPE.
5. One-sentence report phrase
A race between TTY close and device re-registration can free saved termios storage while it is still being updated, producing a heap use-after-free with kernel-crash impact and unresolved post-free write leverage.
6. Manual review recommendation
MANUAL CHECK REQUIRED
The patch establishes a real heap UAF with a stale structured-state write, while attacker control over re-registration, heap replacement, and the final corrupted object remains unresolved.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: tty: fix saved termios reset race [ Upstream
Commit: 1572d86bcf0bcb848d20fc5e5de7ed6963034c2b
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1572d86bcf0bcb848d20fc5e5de7ed6963034c2b
Changed files:
drivers/staging/greybus/uart.c
drivers/tty/tty_io.c
drivers/usb/class/cdc-acm.c
drivers/usb/serial/usb-serial.c
include/linux/tty_driver.h
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=1572d86bcf0bcb848d20fc5e5de7ed6963034c2b
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98750 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98750
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:H/PR:L/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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