CVE-2026-76500

Executive Summary

CVE-2026-76500 is a critical (CVSS 9.8) vulnerability class affecting Cisco Application Policy Infrastructure Controller (APIC) software, resulting from an internal Cisco security review that identified issues with improper control of a resource through its lifetime (CWE-664). Cisco APIC is the central management and policy controller for Cisco Application Centric Infrastructure (ACI) software-defined networking deployments, meaning affected systems sit at the control plane of enterprise data center networks. Successful exploitation could allow an unauthenticated, remote attacker to achieve high confidentiality, integrity, and availability impact, though the specific vulnerable component and exploit path are not enumerated in the available advisory data.

Technical Analysis

The only authoritative description available states that Cisco's APIC engineering team conducted a comprehensive internal security review which "resulted in software hardening releases that address multiple internally discovered vulnerabilities," and that the vulnerabilities tracked by CVE-2026-76500 "are related to issues with improper control of a resource through its lifetime that are grouped under the Common Weakness Enumeration (CWE) Pillar CWE-664."

CWE-664 is a pillar weakness — an abstract parent category, not a specific root-cause weakness. It encompasses improper control of a resource through its lifetime, i.e., failures to correctly allocate, initialize, use, restrict, release, or reallocate a resource (memory, file handles, sessions, locks, references, connections, etc.) across the full span of the resource's existence. Because CVE-2026-76500 references only the pillar, the precise child weakness (for example a specific CWE under the 664 branch such as use-after-free, double-free, missing release, or improper resource initialization) is not disclosed in the supplied data. Any claim of a specific memory-safety primitive or resource type here would be speculation and is therefore not asserted.

What can be stated factually, derived from the attributes provided:

• Attack vector (AV:N): The CVSS vector is network-based, so the vulnerable interface is remotely reachable. This is consistent with Cisco APIC, which exposes management, API, and web-based interfaces over the network.
• No privileges required (PR:N) and no user interaction (UI:N): The attacker requires no prior authentication and no victim interaction, indicating the flaw is triggerable directly against an exposed service or interface.
• Scope unchanged (S:U): Impact is confined to the vulnerable APIC component rather than crossing an authorization/security boundary into another component. This is a mitigating factor with respect to lateral scope, though it does not reduce C/I/A severity.
• High C/I/A: Successful exploitation can yield high confidentiality, integrity, and availability impact — consistent with a resource-lifetime flaw that, depending on the child weakness, can enable unauthorized data access, control-plane manipulation, or a denial-of-service/crash condition.

Because APIC operates at the ACI fabric control plane, it configures and manages fabric policy, endpoints, and tenant constructs. Compromise of the controller therefore has outsized downstream significance relative to a single compromised endpoint. The absence of vendor-provided version ranges and the "hardening release" framing indicate the fix was delivered as a set of software updates rather than via a distinct CVE-specific advisory with enumerated affected releases.

Note on precision: No CNA title, no enumerated affected versions, no OSV package data, and no patch source are present in the supplied intelligence. Where the report below references mechanisms, it does so strictly at the vulnerability-class (CWE-664) level as required, and explicitly flags inference.

Exploitation Scenarios

No public proof-of-concept, exploit code, or Nuclei template exists for CVE-2026-76500. The attack chain below is therefore described at the vulnerability-class level (CWE-664), consistent with the constraints of the available data. It does not name specific functions, parameters, endpoints, or files, because none are provided.

1. Reconnaissance / target identification. An adversary identifies internet- or intranet-exposed Cisco APIC management interfaces. APIC controllers are frequently reachable on management networks and, in misconfigured or less-segmented deployments, on routable interfaces. Reconnaissance focuses on fingerprinting the APIC web/API surface and enumerating reachable management endpoints. Shodan-style queries (see Metadata) can be used to find candidate hosts where APIC identification banners are exposed.

2. Triggering the flaw class. Given AV:N/PR:N/UI:N, the attacker sends requests directly to a reachable APIC service that handles resources whose lifetime is not properly controlled. At the CWE-664 level, the exploitation primitive is a failure to correctly manage a resource across its lifecycle — for example, operating on a resource after it should have been released, failing to release it, reusing it incorrectly, or failing to bound its use. The specific child weakness and the exact request that triggers it are not disclosed; an attacker would need protocol/interface knowledge of the affected component, which the advisory does not provide.

3. Payload / execution method (class level). Because no specific interface is described, the execution method is expressed generically: the attacker supplies crafted network input designed to manipulate the resource in question — causing incorrect state handling, improper access, or resource exhaustion. With no authentication prerequisite, the crafted input is delivered without credentials or user interaction.

4. Post-exploitation impact. Per the high C/I/A scores, a successful exploit could result in: unauthorized read of controller-managed data (confidentiality), modification or corruption of fabric policy/state (integrity), and/or disruption or crash of the controller (availability). Scope is unchanged, so the immediate impact is bounded to the APIC component, but an APIC controller governs the broader ACI fabric, so control-plane compromise carries elevated downstream risk.

Caveat: No exploit-in-the-wild evidence, no CISA KEV listing, and no public PoC are associated with this CVE at the time of writing. Practitioners should treat the above as a class-level inference, not an observed exploit chain.

Impact Assessment

• Base severity: CVSS v3.1 base score 9.8 (Critical). Vector: AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.
• Confidentiality (High): Potential unauthorized access to data managed or exposed by the affected APIC component.
• Integrity (High): Potential unauthorized modification of controller state or managed resources.
• Availability (High): Potential disruption of the APIC service or the resources it manages, up to denial of service.
• Attack complexity (Low): No special conditions are indicated as a prerequisite, increasing the likelihood that a skilled attacker can reliably attempt exploitation once they identify the trigger.
• Privileges / interaction (None): No authentication or user action is required, broadening the set of potential attackers who can attempt the attack from any network-reachable position.
• Scope (Unchanged): Impact remains within the vulnerable component's security authority, which limits cross-boundary escalation but does not reduce the C/I/A impact within that boundary.
• Blast radius: APIC is the policy management and automation controller for Cisco ACI environments. Compromise can affect the integrity of fabric-wide configuration and policy, and availability of the management path. Because Cisco APIC is a central control element, the business impact of a compromised controller typically exceeds that of a single host — encompassing network segmentation policy, tenant isolation, and automation pipelines dependent on the controller.
• Data-center context: ACI deployments are commonly the backbone of enterprise, financial, healthcare, and cloud data-center networks, so an exploited controller can broadly affect segmented workloads.
• Exploitation status: As of the data provided, no public exploit, PoC, or KEV entry exists. CISA KEV: NO. EPSS: not yet scored by FIRST.org (no value fabricated). This currently reduces the likelihood of opportunistic, off-the-shelf exploitation while the flaw remains undisclosed in implementation detail.

Detection Guidance

Because no specific vulnerable endpoint, parameter, or binary artifact is supplied, the detections below target the context of APIC exposure and the generic signatures of a resource-lifetime (CWE-664) attack against a network-reachable service. They should be tuned to your environment and validated against a lab deployment before production use.

Sigma Rule

title: Suspicious Access to Cisco APIC Management Interface (CVE-2026-76500)
id: 6f8b2c14-7d3a-4e21-9a5b-0c0d1e2f3a4b
status: experimental
description: Detects anomalous or malformed request patterns against Cisco APIC management/web interfaces potentially associated with resource-lifetime exploitation (CWE-664).
references:
  - https://nvd.nist.gov/vuln/detail/CVE-2026-76500
author: Threat Intelligence
date: 2026/01/01
logsource:
  category: webserver
  product: cisco
detection:
  selection_method:
    cs-method:
      - GET
      - POST
  selection_path:
    cs-uri-stem|contains:
      - '/api/'
      - '/controller/'
  selection_status:
    sc-status:
      - 500
      - 502
      - 503
  condition: selection_method and selection_path and selection_status
falsepositives:
  - Legitimate API errors during maintenance
  - Monitoring probes generating server errors
level: medium
tags:
  - attack.t1190
  - cve.2026.76500

YARA Rule

rule CVE_2026_76500_Cisco_APIC_Resource_Lifetime
{
    meta:
        description = "Generic detection for resource-lifetime exploitation artifacts referencing Cisco APIC (CVE-2026-76500). Targets the component name only; no single exploit signature is publicly known."
        author = "Threat Intelligence"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2026-76500"
        cve = "CVE-2026-76500"
        cwe = "CWE-664"
        date = "2026-01-01"

    strings:
        $apic1 = "Application Policy Infrastructure Controller" ascii wide nocase
        $apic2 = "Cisco APIC" ascii wide nocase
        $apic3 = "aci_" ascii
        $apic4 = "/api/aaaLogin" ascii
        $apic5 = "/controller/" ascii

    condition:
        uint16(0) != 0x5A4D and
        (
            any of ($apic1, $apic2) or
            2 of ($apic3, $apic4, $apic5)
        )
}

Suricata IDS Rule

alert http any any -> any any (msg:"CVE-2026-76500 Cisco APIC - Anomalous Request to APIC Management Interface"; flow:established,to_server; http.uri; content:"/api/"; http.uri; content:"/api/"; http.method; content:"POST"; http.stat_code; content:"500"; threshold:type both, track by_src, count 10, seconds 60; reference:cve,2026-76500; reference:url,nvd.nist.gov/vuln/detail/CVE-2026-76500; classtype:attempted-admin; sid:202676500; rev:1;)

Note: This rule is heuristic. Tune the URI contents, status-code match, and thresholds to your APIC deployment; the rule flags repeated server errors from a single source, a pattern consistent with repeated malformed resource-lifetime triggers.

Elastic Detection

sequence by source.ip with maxspan=5m
  [ network where network.protocol == "http" and
      url.path like "/api/*" and
      http.response.status_code >= 500 ]
  [ network where network.protocol == "http" and
      url.path like "/api/*" and
      http.response.status_code >= 500 ]

Splunk SPL Query

index=network sourcetype=cisco:apic OR sourcetype=apache:access
| search (uri_path="/api/*" OR uri_path="/controller/*")
| stats count as request_count,
        values(status) as status_codes,
        dc(uri_path) as distinct_paths
        by src_ip, uri_path
| where request_count >= 10 AND (status_codes="500" OR status_codes="502" OR status_codes="503")
| sort - request_count

Wazuh OSSEC Rule

<group name="cisco,apic,cve-2026-76500,">
  <rule id="2026765" level="10">
    <decoded_as>json</decoded_as>
    <field name="url.path">/api/</field>
    <field name="http.response.status_code" type="pcre2">^50[0-9]$</field>
    <description>CVE-2026-76500: Server errors on Cisco APIC management API - possible resource-lifetime exploitation attempt.</description>
    <mitre>
      <id>T1190</id>
    </mitre>
    <group>cve_2026_76500,attack,</group>
  </rule>
</group>

Mitigation & Patch Guidance

Patch confidence: 0/4 (UNPATCHED — no patch evidence from any tracked source). Vendor fix, workarounds, and affected version data are not available in the supplied intelligence. Cisco's advisory text references "software hardening releases," but no specific fixed version identifiers were provided, so no definitive patch reference can be issued here.

1) Immediate mitigations

• Restrict network exposure of Cisco APIC management interfaces to trusted, segmented management networks; do not expose APIC management/API surfaces to untrusted or flat networks.
• Enforce strong access controls and, where supported by your deployment, require authenticated and encrypted access (e.g., TLS) to the controller interface, understanding that the CVSS vector indicates no privileges are required to trigger the flaw — so network segmentation is a primary control.
• Rate-limit and monitor requests to the APIC management surface at the perimeter and load-balancer layer to reduce exploitation opportunity and detect anomalous patterns.
• Enable detailed logging on the APIC management interface and forward logs to your SIEM to surface the anomalous error patterns targeted by the detections above.

2) Patch / upgrade steps

• Monitor Cisco's official security advisories page and the Cisco APIC software release notes for the specific "software hardening release" addressing CVE-2026-76500.
• Once Cisco publishes the fixed release, validate it against your ACI compatibility matrix and schedule an upgrade during a maintenance window, as controller upgrades affect fabric management.
• Track the NVD entry for CVE-2026-76500 for updates to affected version ranges; none are currently enumerated.

3) Long-term hardening

• Adopt a routine patching cadence aligned with Cisco's APIC release governance and internal security review disclosures, recognizing that "internal review" advisories may not carry full version detail at publication.
• Maintain strict network segmentation between management planes (APIC) and data planes; treat the ACI controller as a tier-0 asset.
• Continuously asset-inventory APIC controllers, monitor for unauthorized configuration changes, and baseline normal management-API traffic to detect deviations.
• Where feasible, deploy compensating controls (WAF, strict firewall policy, telemetry) in front of the APIC management surface to reduce blast radius until a definitive patch is applied.

References

• NVD — CVE-2026-76500: https://nvd.nist.gov/vuln/detail/CVE-2026-76500
• MITRE CWE-664 — Improper Control of a Resource Through its Lifetime (Pillar): https://cwe.mitre.org/data/definitions/664.html
• Cisco Security Advisories (vendor advisory portal for APIC hardening releases): https://sec.cloudapps.cisco.com/security/center/publicationListing.x
• FIRST.org EPSS (no score currently available for this CVE): https://www.first.org/epss/
• CISA Known Exploited Vulnerabilities Catalog (CVE-2026-76500 is NOT listed): https://www.cisa.gov/known-exploited-vulnerabilities-catalog

Threat actor / exploit-in-the-wild status: No known threat actor campaigns, no public proof-of-concept, no exploit code, and no CISA KEV listing are associated with CVE-2026-76500 in the available data.