CVE-2026-88102

Executive Summary

CVE-2026-88102 is a use-after-free (CWE-416) vulnerability in Microsoft Windows Failover Cluster that allows an unauthorized, unauthenticated attacker to execute arbitrary code over a network. With a CVSS v3.1 base score of 9.8, the flaw is remotely reachable, requires no privileges, no user interaction, and no prior authentication, making it one of the highest-severity exposure classes possible for a networked Windows service component. Any environment running Windows Failover Cluster services that expose the relevant cluster communication interfaces to an untrusted network segment is potentially at risk, and no vendor patch, public proof-of-concept, or Nuclei template has been observed at the time of writing.

Technical Analysis

CVE-2026-88102 is classified as CWE-416, Use After Free. This weakness class occurs when a program continues to reference a memory object after that object has been deallocated. In a remotely reachable service, the typical sequence is: the service parses attacker-controlled input, allocates and then frees a buffer or heap structure during normal request handling, and subsequently dereferences a stale pointer to that freed memory. If the freed allocation can be reclaimed by attacker-controlled data (a technique commonly referred to as heap grooming or heap feng shui), the stale pointer read/write can be steered to attacker-influenced memory contents.

The NVD description explicitly places this flaw in Windows Failover Cluster and states that exploitation yields code execution over a network by an unauthorized attacker. The CVSS vector — AV:N/AC:L/PR:N/UI:N — confirms that the vulnerable code path is reachable across a network boundary with low attack complexity, without credentials, and without inducing any action from a legitimate user. The scope subscore is Unchanged (S:U), meaning the impact is confined to the vulnerable component's security authority rather than crossing a privilege boundary into other components. Confidentiality, Integrity, and Availability are each rated High (C:H/I:H/A:H), which is consistent with an attacker achieving code execution in the context of the affected cluster service process.

No CNA title, affected version enumeration, or patch reference was supplied with this record. As a result, the specific parsing routine, the affected binary, the exact wire protocol or RPC interface, the offset at which the stale pointer is dereferenced, and the allocation/deallocation call sites are not available from the provided data and are not asserted here. What can be stated with confidence is the vulnerability class (use-after-free), the affected product area (Windows Failover Cluster), the access vector (network), the required privilege level (none), and the outcome (remote code execution). Cluster service components typically communicate over RPC and SMB-adjacent channels with peer nodes, management tooling, and cluster-aware applications; those interfaces constitute the plausible attack surface, but the precise interface for this CVE is not specified in the supplied intelligence and is not invented in this report.

Because the record is unpatched with no evidence of a fix from any tracked source, defenders must treat the flaw as a live, exploitable condition until Microsoft publishes remediation. No public proof-of-concept or exploit code is known, so the exploitation chain below is described at the vulnerability-class level.

Exploitation Scenarios

No public PoC is available; the attack chain below is inferred from the vulnerability class and the network-reachable, unauthenticated characteristics stated in the NVD description.

1) Reconnaissance / target identification. An adversary first enumerates reachable Windows hosts exposing Failover Cluster services. Because the vulnerability is network-reachable and requires no credentials (PR:N, AV:N), the attacker does not need to be a domain member or hold any cluster role. Discovery can be performed through host and service enumeration of the cluster management and inter-node communication ports, and through banner/version fingerprinting of the exposed service to determine whether the target is a Windows host participating in a failover cluster.

2) Triggering the use-after-free. The attacker sends crafted network traffic to the vulnerable cluster-facing service. During processing of the malformed request, the service frees a heap object that is still referenced afterward. The precise message structure, field, or protocol verb that induces the free-then-dereference sequence is not specified in the supplied data and cannot be enumerated without the vendor advisory or binary analysis. At the class level, the attacker's goal at this stage is simply to drive the service into a state where a dangling pointer is dereferenced.

3) Achieving code execution. After a dangling reference is produced, the attacker attempts to reclaim the freed heap region with controlled data (heap grooming) so that the subsequent stale-pointer access resolves to attacker-influenced contents. In use-after-free bugs that lead to remote code execution, this commonly converts into control-flow influence such as a corrupted function pointer or virtual call target. The attacker directs execution to a payload staged in memory, resulting in code execution within the security context of the affected cluster service process — which on Windows cluster nodes typically runs with elevated system privileges.

4) Post-exploitation impact. Successful exploitation grants remote code execution with the integrity, confidentiality, and availability impact rated High by the CVSS vector. In practical terms, a compromised cluster service process on a Windows node gives the attacker a foothold on a high-value server that frequently holds cluster configuration, shared-storage access, and privileged service credentials. From there an attacker would be positioned to move laterally across cluster peers, tamper with or deny cluster services (High availability impact), and read or modify cluster-managed data (High confidentiality and integrity impact). The Unchanged scope rating means the immediate impact is bounded to the vulnerable component's authority, though lateral movement from a compromised cluster node remains a significant escalation path in real deployments.

Impact Assessment

The CVSS v3.1 base score is 9.8 (Critical) with vector CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

• Attack Vector (AV:N): Exploitation occurs over a network, not from an adjacent or local context. Any exposure of the affected cluster service to an untrusted segment or the internet materially raises risk.
• Attack Complexity (AC:L): No specialized conditions beyond delivery of crafted requests are implied; the attacker is not required to win a race or defeat an unusual mitigation as a precondition.
• Privileges Required (PR:N): No authentication or authorization is needed — the attacker is "unauthorized" per the NVD description.
• User Interaction (UI:N): No victim action is required; this is a wormable-style, headless trigger profile.
• Scope (S:U): Impact is confined to the vulnerable component's security authority.
• Confidentiality / Integrity / Availability (C:H/I:H/A:H): Full compromise of the three security objectives for the affected component.

Business impact: Windows Failover Cluster underpins high-availability workloads — databases, file shares, and business-critical clustered applications. A remotely exploitable, unauthenticated use-after-free in this stack means a single crafted network request could potentially lead to arbitrary code execution on an availability-critical server. Because clusters are typically architected as trusted, tightly coupled peer groups, a compromise of one node can translate into control over shared resources and cluster-wide operations. The Unchanged scope constrains immediate blast radius to the component, but the privileged context and cluster topology elevate second-order risk.

Blast radius: Any Windows Failover Cluster node exposing the affected service to an untrusted network is in scope. The unauthenticated, no-interaction trigger profile makes this attractive for opportunistic scanning and self-propagating exploitation. EPSS has not yet scored this CVE, and it is not listed in CISA KEV, so there is currently no evidence of mass exploitation — but the technical characteristics justify treating it as high urgency pending patch availability.

Detection Guidance

Detection for a use-after-free RCE is inherently behavioral: there is no single payload signature, and exploitation may be delivered in many encodings. The rules below focus on the process, network, and memory-corruption telemetry that exploitation of a Windows cluster service would generate. Field names and event IDs used are standard Windows/Sysmon telemetry; no vulnerability-internal identifiers are invented.

Sigma Rule

title: Potential Exploitation of Windows Failover Cluster Use-After-Free (CVE-2026-88102)
id: 8f2c1a44-9b7e-4f01-b3a2-cve202688102
status: experimental
description: Detects suspicious child processes, crashes, or code-execution behavior associated with the Windows Failover Cluster service, consistent with attempted exploitation of CVE-2026-88102 (use-after-free RCE).
references:
  - https://nvd.nist.gov/vuln/detail/CVE-2026-88102
author: valtersit.com
date: 2026/01/01
logsource:
  product: windows
  category: process_creation
detection:
  selection_parent:
    ParentImage|endswith:
      - '\clussvc.exe'
      - '\ClusSvc.exe'
  selection_susp_child:
    Image|endswith:
      - '\cmd.exe'
      - '\powershell.exe'
      - '\pwsh.exe'
      - '\wscript.exe'
      - '\cscript.exe'
      - '\mshta.exe'
      - '\rundll32.exe'
      - '\certutil.exe'
  condition: selection_parent and selection_susp_child
fields:
  - ParentImage
  - Image
  - CommandLine
  - User
falsepositives:
  - Legitimate cluster maintenance scripts invoking administrative tooling
level: high
tags:
  - attack.t1190
  - cve.2026.88102

YARA Rule

rule CVE_2026_88102_Windows_Failover_Cluster_UAF
{
    meta:
        description = "Heuristic detection for artifacts associated with CVE-2026-88102 Windows Failover Cluster use-after-free exploitation"
        author = "valtersit.com"
        date = "2026-01-01"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2026-88102"
        severity = "critical"

    strings:
        $mz = { 4D 5A }
        $pe = { 50 45 00 00 }
        $clus1 = "clusapi" ascii nocase
        $clus2 = "ClusSvc" ascii nocase
        $clus3 = "Failover Cluster" ascii wide nocase
        $uaf1 = "use-after-free" ascii nocase
        $uaf2 = "heap spray" ascii nocase
        $uaf3 = "VirtualAlloc" ascii

    condition:
        $mz at 0 and $pe and 2 of ($clus*) and 1 of ($uaf*)
}

Suricata IDS Rule

alert tcp $EXTERNAL_NET any -> $HOME_NET any (msg:"CVE-2026-88102 Windows Failover Cluster Potential Exploitation Attempt"; flow:established,to_server; dsize:>256; content:"|05 00|"; depth:2; threshold:type limit, track by_src, count 5, seconds 60; classtype:attempted-admin; reference:cve,2026-88102; reference:url,nvd.nist.gov/vuln/detail/CVE-2026-88102; sid:90088102; rev:1;)

Elastic Detection

sequence by host.id with maxspan=30s
  [ process where event.type == "start" and
      process.parent.name : "clussvc.exe" ] with runs=1
  [ process where process.name : ("cmd.exe","powershell.exe","pwsh.exe","wscript.exe","cscript.exe","mshta.exe","rundll32.exe") and
      process.parent.name : "clussvc.exe" ]

Splunk SPL Query

index=windows (source="XmlWinEventLog:Microsoft-Windows-Sysmon/Operational" OR source="WinEventLog:Security")
(EventCode=4688 OR EventCode=1)
| search (ParentProcessName="*\\clussvc.exe" OR ParentImage="*\\ClusSvc.exe")
| search (NewProcessName IN ("*\\cmd.exe","*\\powershell.exe","*\\pwsh.exe","*\\wscript.exe","*\\cscript.exe","*\\mshta.exe","*\\rundll32.exe","*\\certutil.exe"))
| stats count min(_time) as first_seen max(_time) as last_seen values(NewProcessName) as child_procs values(CommandLine) as cmdlines by ComputerName, User
| where count >= 1
| sort - last_seen

index=windows source="WinEventLog:Application"
| search "clussvc" (EventCode=1000 OR EventCode=1001 OR "Application Error")
| stats count values(Message) as crash_detail by ComputerName

Wazuh OSSEC Rule

<group name="windows,cve-2026-88102,">
  <rule id="100881" level="12">
    <if_sid>60000</if_sid>
    <field name="win.eventdata.parentImage">\\clussvc\.exe$</field>
    <field name="win.eventdata.image">\\(cmd|powershell|pwsh|wscript|cscript|mshta|rundll32|certutil)\.exe$</field>
    <description>CVE-2026-88102: Suspicious child process spawned by Windows Failover Cluster service - possible exploitation</description>
    <mitre>
      <id>T1190</id>
    </mitre>
  </rule>

  <rule id="100882" level="10">
    <if_sid>60000</if_sid>
    <field name="win.system.providerName">Application Error</field>
    <match>clussvc.exe</match>
    <description>CVE-2026-88102: Windows Failover Cluster service crash - possible use-after-free exploitation attempt</description>
  </rule>
</group>

Mitigation & Patch Guidance

Patch confidence: 0/4 (UNPATCHED — no patch evidence from any tracked source). No vendor fix, workaround, or affected version range has been published for this record. There is no confirmed remediation; the following guidance is defensive.

1) Immediate mitigations

• Restrict network exposure of Windows Failover Cluster services. Segment cluster nodes onto dedicated, tightly firewalled management networks and block cluster communication ports from untrusted segments and the internet. Given AV:N/PR:N/UI:N, reducing reachability directly reduces exploitability.
• Enforce Windows Firewall / host firewall rules that allow cluster traffic only between authorized cluster peers and management hosts.
• Disable or constrain unnecessary cluster-management interfaces and ensure only required roles and features are installed on cluster nodes.
• Monitor availability and crash telemetry for clussvc.exe; repeated service crashes may indicate fuzzing or exploitation attempts (see detection rules above).
• Restrict east-west traffic between cluster nodes using the principle of least privilege, limiting an attacker's ability to pivot if a node is compromised.

2) Patch / upgrade steps

• No patch is currently available. Continuously monitor the Microsoft Security Update Guide and the NVD entry for CVE-2026-88102 for a vendor advisory and fixed build. Because version data is absent, map every Windows host running Failover Cluster services and baseline the currently installed cluster/cluster-service build so patches can be applied promptly the moment they are released.
• Subscribe to CISA advisories and Microsoft product-specific channels for emerging detail; treat any future CVSS re-scoring or KEV listing as an escalation trigger.

3) Long-term hardening

• Maintain an asset inventory of all cluster nodes and their exposed network interfaces; revalidate segmentation on a recurring basis.
• Apply the Windows security baseline and prioritize memory-corruption mitigations (ASLR, CFG, DEP) — these are defense-in-depth and do not eliminate the flaw.
• Adopt a rapid patch-management workflow for high-availability server tiers, and rehearse emergency patching for clusters where downtime windows are constrained.
• Deploy the detection content in the previous section and tune it against normal cluster maintenance activity to reduce false positives while retaining sensitivity.

References

• NVD — CVE-2026-88102: https://nvd.nist.gov/vuln/detail/CVE-2026-88102
• CWE-416 — Use After Free (MITRE): https://cwe.mitre.org/data/definitions/416.html
• Microsoft Security Update Guide (monitor for CVE-2026-88102 advisory): https://msrc.microsoft.com/update-guide
• CISA Known Exploited Vulnerabilities catalog (check for future listing): https://www.cisa.gov/known-exploited-vulnerabilities-catalog
• FIRST EPSS (CVE not yet scored at time of writing): https://www.first.org/epss/

Threat actor / exploitation status: No exploit code, public PoC, or Nuclei template is known for this CVE, and it is not listed in CISA KEV. EPSS has not yet been assigned. There is no observed evidence of in-the-wild exploitation as of the data provided; the attack-chain discussion is inferred from the vulnerability class.