* [CVE-2026-99122][IMPORTANT] vsock/vmci: validate packet source for connected sockets [ Upstream
@ 2026-10-29 4:45 21% AL-KERNEL
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From: AL-KERNEL @ 2026-10-29 4:45 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-99122
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: NO
Patch: vsock/vmci: validate packet source for connected sockets [ Upstream
Commit: c027f8b429dbb2157fc1b503df196e272d947c89
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c027f8b429dbb2157fc1b503df196e272d947c89
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99122
Analysis date: Thu, 29 Oct 2026 00:45:00 -0400
ActionableScore: 7
ActionableScore lower bound: unknown
Actionable bucket: Strong Important candidate
Manual review required: YES
Summary:
A VMCI context can inject a control packet into another context’s connected socket because destination-only fallback omitted peer-source validation, with an unauthorized connection reset demonstrated.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-99122 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99122
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-2026-99122 IMPORTANT https://www.kernelcve.org/list/?q=CVE-2026-99122 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=2 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:N/I:L/A:H';CWE-346;CWE-345;*CWE-20;Other CVSS 'AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:L';BEST CVSS score: '7.1';DESCR 'vmci_transport_recv_stream_cb could select a connected or connecting socket through its destination only bound table fallback without verifying that the packet source matched the stored peer. An attacker controlling a different VMCI context can send a control packet such as RST and alter the state of a socket belonging to another context. The demonstrated result is an unauthorized reset of a TCP_SYN_SENT socket and denial of service for that connection. For the CVSS the PR:N value is selected because no prior authorization in the target context is required once the attacker can send VMCI packets from another reachable context. AV:A reflects the VMCI context boundary rather than Internet reachability. No memory corruption or confidentiality primitive is shown. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 7.1 and the production ActionableScore returned 7 with recommendation Strong Important candidate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage LOW to MODERATE_KPANIC because the ActionableScore threshold rule was applied. ActionableScore thresholds stage MODERATE_KPANIC to IMPORTANT because the ActionableScore threshold rule was applied. final reconciliation stage IMPORTANT to IMPORTANT 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 produced a review artifact and its decision was processed by the applicable downgrade and preservation rules. Exact triggered rule markers were INCREASED_TO_MODERATE7_FROM_LOW_BASED_ON_GUESSCVSS_AND_ACTIONABLESCOREHIGHER4 and INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHERTHAN5 and TEMP_KPANIC_MERGE_IMPORTANT_WINS and KPANIC_UNSUPPORTED_REMOVED. The independent weaker Aegis shadow evaluated CVSS 5.4 and ActionableScore 2 with primitive class CLASS_C 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 Strong Important candidate (with actual score 7) MAYBE INIT LEAK PACKET INCREASED_TO_MODERATE7_FROM_LOW_BASED_ON_GUESSCVSS_AND_ACTIONABLESCOREHIGHER4 INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHERTHAN5 TEMP_KPANIC_MERGE_IMPORTANT_WINS KPANIC_UNSUPPORTED_REMOVED - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=7
PrimitiveClass=CLASS_A
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
RequiresHostUID0=NO
AuthorizationDecisionBypass=YES
ProtectedResourceImpact=CONFIRMED
B4PendingReview=YES
B4PendingConfirmed=YES
1. ActionableScore
* Raw base score: 7.
* Conservative score: 7; no floor or cap applied.
* Raw paranoid score: 7.
* Paranoid score: 7; no additional speculative effects scored.
* Final recommended bucket: **Strong Important candidate**::
2. Signal breakdown
* +2 — Adjacent/VMCI-context reachability: an attacker controlling another reachable VMCI context can deliver the packet without authorization in the target context.
* +2 — Concrete authorization decision bypass: destination-only lookup selects a connected/non-listening socket without validating the packet source against its stored peer, changing rejection into packet acceptance.
* +1 — Integrity impact: the unauthorized RST changes another context’s socket state.
* +1 — Availability impact: the demonstrated result resets a `TCP_SYN_SENT` connection.
* +1 — Practical exploit chain: foreign VMCI context → destination-only fallback → forged RST accepted → victim connection reset.
* No memory corruption, UAF, disclosure, LPE, arbitrary access, or host-wide crash is shown.
* No extra score for helper fan-out or hypothetical effects on other packet types.
3. Reachability analysis
The evidenced attacker controls a separate VMCI context and needs no authorization in the victim context. The supplied reproduction grounds the complete cross-context RST path and supports `HostAdminRequired=NO` and `RequiresHostUID0=NO`; this is adjacent VMCI reachability, not Internet-remote reachability. Linux user/net namespace capability scope is not established and is irrelevant to the demonstrated VMCI-context boundary. No race penalty applies: locking determines where validation must be repeated, but the unauthorized reset itself is reproduced rather than dependent on a proven narrow race.
4. Primitive and severity reading
The exact primitive is peer-authentication bypass for an active connected/connecting socket. The vulnerable destination-only fallback accepts a packet from a source other than `vsk`’s stored peer. The fix cleanly restores protection by calling `vsock_check_source()` under the socket lock in both bottom-half and deferred-work paths.
B4-PENDING is confirmed: `vmci_transport_recv_stream_cb()` changes the expected source-mismatch DENY into ALLOW, and the protected resource is the victim context’s live socket state. The demonstrated unauthorized reset establishes cross-context integrity and connection availability impact, but not kernel-memory corruption or privilege escalation. Class A and mandatory review are warranted; auto-downgrade would discard a concrete cross-context authorization bypass.
5. One-sentence report phrase
A VMCI context can inject a control packet into another context’s connected socket because destination-only fallback omitted peer-source validation, with an unauthorized connection reset demonstrated.
6. Manual review advice
MANUAL CHECK REQUIRED
B4-PENDING is confirmed through a concrete below-host-admin cross-context DENY-to-ALLOW path affecting protected socket state.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: vsock/vmci: validate packet source for connected sockets [ Upstream
Commit: c027f8b429dbb2157fc1b503df196e272d947c89
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c027f8b429dbb2157fc1b503df196e272d947c89
Changed files:
net/vmw_vsock/vmci_transport.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=c027f8b429dbb2157fc1b503df196e272d947c89
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-99122 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99122
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:N/I:L/A:L
The Best / paranoid CVSS vector: AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:L/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: unknown
Paranoid ActionableScore: 7
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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