CVE-2026-88115

Executive Summary

CVE-2026-88115 is an out-of-bounds read vulnerability (CWE-125) in the Windows Server implementation of the Network File System (NFS) service. An unauthorized attacker can trigger the flaw over the network and, per the CVSS vector (AV:N/AC:L/PR:N/UI:R), achieve code execution with High confidentiality, integrity, and availability impact. Organizations exposing NFS interfaces on Windows Server are the primary exposure group, and exploitation requires no prior authentication.

The CVSS 3.1 base score is 8.8 (High), reflecting a network-reachable, low-complexity attack requiring only a degree of user interaction. No public proof-of-concept, Nuclei template, or exploit code is currently available, and the CVE is not listed in CISA KEV. As of this writing, no vendor patch has been confirmed through tracked sources, meaning the vulnerability is effectively unpatched and mitigations must rely on network hardening and compensating controls.

Technical Analysis

The vulnerability class is an out-of-bounds read, codified as CWE-125. Out-of-bounds reads occur when a program accesses memory at an index, offset, or length that exceeds the bounds of the allocated buffer. In the context of the Windows Server NFS implementation, the vulnerable component operates as a network-facing service: NFS requests are received over the network, parsed, and dispatched to handlers that read from memory-backed buffers. When an attacker supplies a crafted request that induces the service to read past the end of a buffer, the result can range from information disclosure (leaking heap or stack memory) to a crash or, in certain memory-corruption chaining scenarios, controlled code execution.

The NVD description states plainly: "Out-of-bounds read in Windows Server for NFS allows an unauthorized attacker to execute code over a network." This confirms the attack surface (NFS over the network), the authorization requirement (none — unauthorized attacker), and the objective (code execution). Importantly, the description does not identify specific function names, protocol procedures, or file paths, so precise code-level analysis cannot be provided without additional vendor detail. The mechanism should nonetheless be understood at the class level: a length or index field within a network-supplied NFS request is trusted by the service and used to bound a memory read operation without adequate validation, causing the read to exceed the intended buffer.

The CVSS vector indicates AC:L (low complexity), suggesting the trigger conditions are not exotic and that a stable proof-of-concept may be straightforward for a capable adversary. PR:N (no privileges) confirms unauthenticated reach. The UI:R (user interaction required) component is notable for a network service exploitation scenario; it may reflect a requirement for a particular protocol state, an initial mount, or a crafted file interaction that the victim environment performs rather than a direct user click. Because the flaw is network-reachable on the NFS port (typically TCP/UDP 2049, with RPC portmapper at 111), an exposed Windows Server providing NFS exports presents a directly exploitable surface.

Because the vulnerability is an out-of-bounds read rather than a write, the code execution outcome implies a chaining condition: leaked or improperly bounded memory could be used to defeat memory protections, or the read primitive is part of a larger exploitation path. Without a vendor advisory detailing the exact failing code path, any claim about the precise buffer, structure, or protocol field would be speculation and is therefore not asserted here.

Exploitation Scenarios

No public PoC is available; the attack chain described below is inferred from the vulnerability class (CWE-125) and the NVD description. It uses only the components named in the source data (Windows Server for NFS, network reachability, code execution).

1. Reconnaissance / target identification. An adversary scans for hosts exposing NFS. On Windows Server, this means identifying systems with the NFS server role installed and reachable over the network — typically discovered via port 2049 and RPC portmapper (111) scans, or via internet-wide services such as Shodan using the dorks listed in the metadata. The attacker confirms the service is Windows-based NFS and maps accessible exports.

2. Triggering the flaw class. The attacker constructs a network request to the NFS service that manipulates a length, count, or offset value so that the service's internal buffer read runs past the end of the allocated region. Because the defect is an out-of-bounds read, the request does not need to overwrite memory to cause the access; it needs only to induce the parser or handler to dereference beyond the buffer boundary. No authentication is required (PR:N), so the request can be sent to the exposed interface directly.

3. Payload / execution method at the vulnerability-class level. The out-of-bounds read yields a read primitive against process memory. Attackers may leverage the leaked contents (for example, to bypass ASLR or infer memory layout) and then extend the primitive toward code execution, in line with the NVD statement that the flaw allows code execution over the network. The UI:R rating implies the attack path may depend on a specific interaction or protocol state realized in the target environment.

4. Post-exploitation impact. Successful code execution in the context of the NFS service yields High confidentiality, integrity, and availability impact. The attacker could read or modify files served over NFS, pivot to the host, or disrupt service availability. Because Windows Server for NFS frequently mediates access to shared storage, compromise can expose data beyond the immediate host.

This section deliberately avoids naming functions, structures, or endpoints not present in the source data.

Impact Assessment

With a CVSS 3.1 base score of 8.8, this is a High-severity issue. The subscores explain the risk profile:

• Attack Vector (N): Network — the flaw is exploitable remotely over the network, materially raising risk for any host with NFS exposed.
• Attack Complexity (L): Low — the attacker is not required to overcome unusual conditions or race windows, which lowers the bar for weaponization.
• Privileges Required (N): None — no credentials or prior foothold are needed, enabling unauthenticated attackers.
• User Interaction (R): Required — some interaction or defined protocol state is necessary, slightly constraining mass opportunistic exploitation but not blocking targeted attacks.
• Scope (U): Unchanged — the compromise remains within the vulnerable component's security authority.
• Confidentiality/Integrity/Availability (H/H/H): All three are rated High, consistent with memory corruption enabling code execution and full control of the affected component.

Blast radius. Any Windows Server instance running the NFS server role on a reachable network segment is in scope. Because NFS is commonly used for file sharing across enterprise networks and may be exposed in multi-tenant, cloud, or hybrid environments, a single compromised host can become a pivot point into shared storage and adjacent systems. Availability impact is high, so denial-of-service and service disruption are realistic outcomes even if code execution is not achieved.

Business impact. Data exposure (direct read access to shared file content), integrity loss (tampering with files or host configuration), and operational disruption (service outage) are all plausible. The absence of a patch increases the dwell time available to attackers, and the absence of public exploitation evidence to date is not a reliable indicator of current or future risk.

Detection Guidance

Sigma Rule

title: Potential Windows Server NFS Out-of-Bounds Read Exploitation Attempt
id: 7b2c9f41-4a8e-4d3c-9c21-8f0e2a6d5c11
status: experimental
description: Detects anomalous NFS-related process behavior indicative of exploitation of CVE-2026-88115 (out-of-bounds read in Windows Server for NFS).
references:
  - https://nvd.nist.gov/vuln/detail/CVE-2026-88115
author: Threat Intelligence
date: 2026/01/01
tags:
  - attack.t1190
  - cve.2026.88115
logsource:
  category: process_creation
  product: windows
detection:
  selection_service:
    Image|endswith:
      - '\nfsd.exe'
      - '\services.exe'
  selection_crash:
    EventID: 1000
    Provider: 'Application Error'
    Data|contains:
      - 'nfs'
      - 'NFS'
  condition: selection_service or selection_crash
falsepositives:
  - Legitimate NFS service restarts
  - Administrative maintenance of NFS role
level: medium

YARA Rule

rule CVE_2026_88115_Windows_NFS_OOB_Read_Attempt
{
    meta:
        description = "Scans for artifacts indicative of out-of-bounds read exploitation against Windows Server for NFS (CVE-2026-88115)"
        author = "Threat Intelligence"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2026-88115"
        date = "2026-01-01"
        severity = "high"

    strings:
        $nfs_proc = { 00 00 00 00 } // NFS NULL procedure placeholder
        $nfs_magic = { 00 01 86 A3 } // RPC program number for NFS (100003)
    condition:
        uint16(0) == 0x0000 and any of ($nfs_*)
}

Suricata IDS Rule

alert tcp any any -> any 2049 (msg:"CVE-2026-88115 Windows Server NFS potential out-of-bounds read exploitation attempt"; flow:to_server,established; content:"|00 01 86 A3|"; offset:0; depth:4; threshold:type limit, track by_src, count 5, seconds 60; classtype:attempted-user; reference:cve,2026-88115; reference:url,nvd.nist.gov/vuln/detail/CVE-2026-88115; sid:202688115; rev:1;)

Elastic Detection

sequence by host.id with maxspan=60s
  [process where process.name : "nfsd.exe" and event.action : "start"]
  [process where process.name : "nfsd.exe" and event.action : "end" and process.exit_code != 0]

Splunk SPL Query

index=windows (EventCode=1000 OR EventCode=7031 OR EventCode=7034)
| search (Message="*nfs*" OR Message="*NFS*" OR Faulting_application="*nfsd*")
| stats count earliest(_time) AS first_seen latest(_time) AS last_seen BY host, Faulting_application, Message
| where count > 0
| sort - count

Wazuh OSSEC Rule

<group name="windows,nfs,">
  <rule id="100881" level="8">
    <if_sid>60000</if_sid>
    <field name="win.system.providerName">Application Error</field>
    <field name="win.system.message">\.exe</field>
    <description>CVE-2026-88115: Possible Windows Server NFS out-of-bounds read crash or exploitation attempt</description>
    <mitre>
      <id>T1190</id>
    </mitre>
    <group>cve_2026_88115,</group>
  </rule>
</group>

Mitigation & Patch Guidance

Patch confidence: 0/4 (UNPATCHED — no patch evidence from any tracked source). No vendor fix, workaround, or affected-version data is currently available for CVE-2026-88115. The guidance below is therefore compensating-control focused.

1) Immediate mitigations.

• Restrict network access to NFS (port 2049) and RPC portmapper (111) to trusted hosts and management networks only. Do not expose NFS interfaces to the public internet.
• Segment NFS-hosting servers into dedicated VLANs and enforce host-based firewalls so only approved clients can reach the service.
• If NFS is not operationally required, disable or uninstall the Windows Server NFS role to remove the attack surface entirely.
• Enable application control / WDAC where feasible to limit post-exploitation binary execution.
• Increase monitoring on NFS hosts for abnormal process creation, crashes, and unexpected outbound connections.

2) Patch / upgrade steps.

• Monitor Microsoft's security update channels (MSRC, the Microsoft Security Update Guide) for an advisory addressing Windows Server for NFS. Because no patch exists in tracked sources, no specific KB or build number can be cited here.
• Subscribe to NVD and vendor notifications for CVE-2026-88115 status changes. Validate every claimed "fix" against the authoritative vendor source before applying.
• When a patch becomes available, stage and test it in a non-production environment before broad deployment to NFS servers.

3) Long-term hardening.

• Adopt a vulnerability management workflow that tracks network-facing services and their exposure.
• Enforce least privilege and network ACLs around file-sharing protocols; periodically audit NFS exports and permissions.
• Deploy endpoint detection and response (EDR) with memory-corruption and exploitation-detection capabilities on NFS hosts.
• Maintain offline or immutable backups. Because integrity impact is rated High, recovery from tampering must be possible.
• Where feasible, migrate NFS services to supported, verifiably up-to-date platforms and reduce reliance on unpatched components.

References

• NVD — CVE-2026-88115: https://nvd.nist.gov/vuln/detail/CVE-2026-88115
• MITRE CWE-125 (Out-of-bounds Read): https://cwe.mitre.org/data/definitions/125.html
• MITRE ATT&CK T1190 (Exploit Public-Facing Application): https://attack.mitre.org/techniques/T1190/
• Microsoft Security Update Guide (monitor for Windows Server NFS advisories): https://msrc.microsoft.com/update-guide
• CISA Known Exploited Vulnerabilities Catalog (CVE-2026-88115 not currently listed): https://www.cisa.gov/known-exploited-vulnerabilities-catalog

No known threat actor campaigns or exploit-in-the-wild evidence are associated with CVE-2026-88115 in the data provided. No public PoC, Nuclei template, or exploit code has been identified.