CVE-2026-21399

Executive Summary

CVE-2026-21399 is a heap-based buffer overflow (CWE-122) in the Intel(R) Open Volume Kernel Library (Intel(R) Open VKL) affecting all versions prior to 2.0.2. The vulnerability resides in Ring 3 user applications, is triggerable by an authenticated local user with low attack complexity and no user interaction, and results primarily in denial of service with high availability impact and low integrity impact. Applications that embed Open VKL for volume rendering and scientific visualization are in scope; at the time of writing, no patch has been confirmed by tracked sources.

Technical Analysis

Intel Open VKL is a library that provides volume kernels for high-performance rendering of unstructured and structured volumetric data, commonly integrated into scientific visualization, medical imaging, and engineering simulation pipelines. The NVD description indicates that versions before 2.0.2 contain a heap-based buffer overflow (CWE-122). A heap-based buffer overflow occurs when a code path writes data beyond the boundary of a dynamically allocated heap buffer. The excess write corrupts adjacent heap metadata — chunk headers, size fields, or neighboring user objects — which can corrupt pointers and allocator state. In this case, the description assesses the observable outcome as denial of service: the corrupted heap typically triggers an access violation on a subsequent allocation or free operation, terminating the host process.

The attack surface is strictly local. The adversary must be an authenticated user on the target system, but does not require special internal knowledge of the library internals, and the attack complexity is rated low. No user interaction is required, meaning that the malicious input is processed automatically rather than through a social-engineering step such as clicking a link or opening a file. The overflow executes entirely within Ring 3 (user mode) and does not, by itself, cross privilege boundaries or expose kernel memory.

The CVSS subscores expressed in the description are: confidentiality — none; integrity — low; availability — high for the vulnerable system, with subsequent system-level impacts of none across all three security properties. The low integrity subscore implies that in some code paths the attacker may be able to overwrite a limited amount of adjacent heap content (e.g., a flag or pointer) before the process destabilizes, although the downstream assessment indicates this does not translate into a system-level integrity breach. Insufficient technical detail is available to identify the exact vulnerable function, input structure, or API entry point; no function names, file paths, or parameter names are disclosed in the NVD description or CNA title, and none are inferred in this report.

Exploitation Scenarios

No public PoC is available; the attack chain below is inferred from the vulnerability class (local heap-based buffer overflow triggered by an authenticated user with no interaction) and is explicitly marked as an inference.

1. Reconnaissance / target identification. The adversary requires an authenticated account on a host where an application linked against Open VKL < 2.0.2 is installed — typically a rendering workstation, a batch visualization node, or a simulation server. The attacker enumerates local processes and loaded library images to identify a victim process that consumes volume data through Open VKL (e.g., a renderer or pre-processing daemon).

2. Trigger of the flaw class. The attacker supplies crafted volume-related input to the application. At the vulnerability-class level, the malformed input contains size or count fields that cause the library to perform an undersized heap allocation followed by a write operation that exceeds the allocated bounds. Because no user interaction is required, the input can be placed in a location or data path that the rendering process consumes automatically, such as a shared dataset directory, a batch job queue, or a file watcher directory.

3. Payload / execution method. The library's processing code performs an out-of-bounds write into the heap. The corrupted heap metadata causes a crash during a subsequent allocation, reallocation, or free operation. No code execution is implied by the NVD description; the primary execution outcome is an unhandled exception and process termination.

4. Post-exploitation impact. The immediate impact is denial of service: the rendering application or host process terminates, interrupting visualization pipelines and dependent workflows. The low integrity subscore allows for the possibility of limited data corruption before the crash, but the description assigns no downstream confidentiality or integrity impact. There is no evidence of privilege escalation, lateral movement, or cross-tenant impact from this vulnerability alone.

Impact Assessment

Affected systems. Any deployment of the Intel Open VKL library before version 2.0.2 inside Ring 3 user applications. This includes scientific visualization suites, medical imaging renderers, CAD/CAE post-processors, and in-house rendering pipelines that statically or dynamically link against Open VKL.

Business impact. The vulnerability enables a low-barrier local denial of service once an authenticated foothold exists. In enterprise environments, exploitation can halt rendering workloads, delay engineering and research deliverables, and force operational outages. Because the attack requires only an authenticated local user and low complexity, insider threats or adversaries who have already compromised a low-privilege account can use CVE-2026-21399 to disrupt production systems without further exploitation steps.

Blast radius. The overflow is confined to the affected process memory space; there is no evidence of kernel impact, adjacent-tenant compromise, or network propagation. The description's "subsequent system impacts: none" supports a contained blast radius, limiting the business consequence to availability of the specific rendering service, with a minor integrity subscore that does not rise to system-level compromise.

Exploitability context. The EPSS score is 0.00114 (1.7th percentile of exploited CVEs), indicating a low predicted probability of exploitation in the wild in the near term. CISA has not listed this CVE in the Known Exploited Vulnerabilities catalog (KEV status: NO). No threat-actor campaigns or exploit-in-the-wild evidence were identified. However, the absence of a confirmed patch (patch confidence 0/4) means the vulnerability remains open in all deployments below 2.0.2, and the low complexity and absent user interaction lower the barrier for future weaponization.

Detection Guidance

Detection for CVE-2026-21399 is inherently host-centric: this is a local, memory-corruption vulnerability in a library, so the strongest telemetry sources are application crash events, segmentation faults, and abnormal process terminations in applications that load Open VKL. Network-layer detection is of limited utility; the Suricata rule provided below is a best-effort signal for the delivery of crafted volume datasets to rendering hosts and should not be relied upon as a primary control.

Sigma Rule

title: Windows Crash Event - Intel Open VKL Library (CVE-2026-21399)
id: 6f7c2b4e-8d91-4a3e-9b2f-1c4d5e6f7a8b
status: experimental
description: Detects Windows Application Error (Event ID 1000) and WER (Event ID 1001) events where the faulting module references the Intel Open VKL library, a heuristic indicator of CVE-2026-21399 heap overflow exploitation.
references:
  - https://nvd.nist.gov/vuln/detail/CVE-2026-21399
tags:
  - attack.t1499
  - cve.2026-21399
logsource:
  product: windows
  category: application
detection:
  selection_crash:
    EventID: 1000
    FaultingModule|contains: openvkl
  selection_wer:
    EventID: 1001
    Description|contains: openvkl
  condition: selection_crash or selection_wer
level: high
falsepositives:
  - Non-security crashes in rendering applications that legitimately use Open VKL
  - Development and debug builds of Open VKL

title: Linux SIGSEGV in Open VKL Rendering Process (CVE-2026-21399)
id: 7a8b9c0d-1e2f-4a5b-8c9d-0e1f2a3b4c5d
status: experimental
description: Detects segmentation faults in processes whose image name indicates an Open VKL / OSPRay rendering workload, correlating with heap corruption from CVE-2026-21399.
logsource:
  product: linux
  service: auditd
detection:
  selection:
    type: SEVG
    process|endswith:
      - ospr*
      - *render*
      - *vkl*
  condition: selection
level: high
falsepositives:
  - Driver faults and legitimate rendering bugs
  - Out-of-memory kills misreported as segfaults

YARA Rule

rule Intel_OpenVKL_CVE_2026_21399_Artifacts
{
    meta:
        author = "Valtersit CTI"
        description = "Flags PE binaries, crash dumps, and memory images referencing the Intel Open VKL library targeted by CVE-2026-21399."
        cve = "CVE-2026-21399"
        cwe = "CWE-122"
        date = "2026"
    strings:
        $s1 = "openvkl" ascii wide nocase
        $s2 = "Open Volume Kernel Library" ascii wide nocase
        $s3 = "Open VKL" ascii wide nocase
    condition:
        uint16(0) == 0x5A4D and any of ($s*)
}

Note: the rule matches the library's identifying strings, which appear verbatim in the CVE description. It is designed to identify in-scope binaries and crash artifacts for triage, not to detect the overflow write itself.

Suricata IDS Rule

alert http any any -> any any (msg:"CVE-2026-21399 - Potential Open VKL Volume Data Delivery to Rendering Host"; flow:established,to_server; content:"openvkl"; nocase; http.uri; reference:cve,2026-21399; classtype:attempted-dos; sid:2026213990; rev:1;)

This rule is a best-effort network indicator alerting on HTTP URIs referencing the Open VKL library during dataset or artifact delivery. Given that the vulnerability is exploited locally, network detection cannot observe the overflow directly; this signal should feed into host-based triage rather than be treated as a standalone detection.

Elastic Detection

// Heuristic: application crashes followed by WER report artifacts, correlated within 1 minute
sequence with maxspan=1m
  [ process where event.code == "1000" and process.name != null ]  // Application Error event
  [ file where event.code == "1001" and wildcard(file.name, "*openvkl*") ] // WER artifact

// Linux: segfault events in rendering process names
process where event.action == "segfault" and wildcard(process.name, "*ospr*", "*render*")

Splunk SPL Query

index=windows EventCode=1000 OR EventCode=1001 (FaultingModule=*openvkl* OR Description=*openvkl*)
| table _time, host, Image, FaultingModule, ReportIdentifier
| eval cve="CVE-2026-21399", tactic="T1499 - Endpoint Denial of Service"
| sort - _time

index=linux sourcetype=linux_audit type=SEGV (*ospr* OR *openvkl* OR *render*)
| table _time, host, process, type, uid
| eval cve="CVE-2026-21399", tactic="T1499 - Endpoint Denial of Service"
| sort - _time

Wazuh OSSEC Rule

<group name="openvkl,cve-2026-21399,">
  <rule id="100345" level="10">
    <decoded_as>syslog</decoded_as>
    <match>segfault|SIGSEGV|general protection fault</match>
    <regex>openvkl|ospr|onvkl</regex>
    <description>Potential CVE-2026-21399 heap corruption: crash in Intel Open VKL rendering process</description>
    <mitre>
      <id>T1499</id>
    </mitre>
    <group>endpoint_dos,</group>
  </rule>
</group>

Detection caveat: all rules are heuristic, as the NVD description does not disclose a specific signature or trigger condition. High-fidelity detection requires the host telemetry above plus baseline tuning of the rendering application's normal crash rate.

Mitigation & Patch Guidance

Patch confidence: 0/4 — UNPATCHED. No vendor advisory, commit, or release has been confirmed by tracked sources, and the affected-versions list is empty in the available intelligence. The NVD description states the flaw exists "before version 2.0.2," indicating that version 2.0.2 or later is intended as the remediation boundary; however, no official patch artifact or advisory has been observed.

1. Immediate mitigations. Restrict local access to systems running Open VKL by enforcing least-privilege accounts and removing unnecessary interactive users. Do not process untrusted or externally sourced volume data sets on rendering hosts until the library is confirmed patched. Isolate rendering/visualization nodes from shared batch queues if those queues ingest third-party data. Deploy and tune the crash-detection rules above to alert on abnormal renderer termination. If feasible, sandbox rendering workloads in containers or VMs to contain the blast radius of a DoS.

2. Patch/upgrade steps. Monitor Intel's Security Center and the official Open VKL release channel. When version 2.0.2 (or later) is published, upgrade all affected deployments, rebuild any statically linked applications, and inventory all binaries that embed or import Open VKL (the YARA rule above can assist). Verify the supply chain integrity of the upgraded library through Intel's official distribution channels and checksum validation before deployment.

3. Long-term hardening. Integrate CVE and EPSS monitoring into the vulnerability management lifecycle so that this CVE and future Open VKL issues are triaged as they are disclosed. Enforce memory-corruption mitigations (ASLR, heap integrity checks, stack canaries) at the operating-system level on rendering hosts. Establish a baseline of rendering-process crash telemetry to reduce false positives in detection rules. Subscribe to Intel security advisory feeds and validate that Open VKL is kept current as part of standard software maintenance.

References

1. NVD Entry — CVE-2026-21399: https://nvd.nist.gov/vuln/detail/CVE-2026-21399
2. Intel Security Center (official advisory feed; no specific advisory tracked for this CVE at time of writing): https://www.intel.com/content/www/us/en/security-center/default.html
3. Intel Open VKL project releases (upgrade target >= 2.0.2): https://github.com/RenderKit/openvkl/releases
4. CISA Known Exploited Vulnerabilities Catalog (CVE not listed; KEV status NO): https://www.cisa.gov/known-exploited-vulnerabilities-catalog
5. MITRE ATT&CK — T1499 Endpoint Denial of Service: https://attack.mitre.org/techniques/T1499/

Threat-actor activity: No known threat-actor campaigns, exploit-in-the-wild evidence, or malware families associated with CVE-2026-21399 were identified. EPSS score 0.00114 (1.7th percentile) corroborates a currently low exploitation likelihood, though the unpatched status warrants ongoing monitoring.