CVE-2026-76453

Executive Summary

CVE-2026-76453 is a software hardening advisory covering multiple internally discovered vulnerabilities in Cisco NX-OS, grouped under CWE-707 (Improper Neutralization). The NVD entry describes a release that addresses several findings rather than a single discrete bug, which means the CVE aggregates issues identified during a Cisco-internal security review.

The CVSS base score is 8.8 (High), with a vector of AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H. The high privileges-required subscore (PR:L) indicates the attacker needs some level of authenticated access, while AC:L/UI:N and scope-unchanged indicate a low-complexity, non-interactive exploit that stays within the vulnerable component's security authority. No affected versions, patch identifiers, PoC code, or Nuclei templates are currently tracked.

Technical Analysis

CWE-707 ("Improper Neutralization") is a broad category class in the Common Weakness Enumeration taxonomy. It refers to failures in neutralization logic — typically where a software component does not correctly sanitize, encode, validate, or otherwise neutralize input before it is consumed by a downstream parser, interpreter, or command engine. In the NVD description provided, the neutralization issues are explicitly attributed to a Cisco NX-OS engineering team internal review, and the resulting fixes are bundled into a hardening release.

Because the NVD description groups multiple internally discovered issues under one CVE and does not enumerate function names, CLI commands, URL endpoints, or daemon behaviors, no code-level reproduction details can be asserted with confidence. The CVSS vector provides the strongest technical signal available:

• AV:N — the attack surface is reachable over the network; the offending input can be delivered remotely rather than requiring local console access.
• AC:L — no special conditions, race windows, or timing dependencies are required beyond the basic prerequisites.
• PR:L — the attacker must first obtain some authenticated or otherwise privileged access context on the target before the neutralization failure can be exercised. This distinguishes the CVE from an unauthenticated remote-code-execution class issue.
• UI:N — no victim interaction is required.
• S:U — the vulnerable component and impacted component are the same; no sandbox or scope escape is implied by the vector.
• C:H / I:H / A:H — high impact on confidentiality, integrity, and availability, consistent with a flaw that can result in broad read/write/availability effects once triggered.

Taken together, the most defensible interpretation from the data provided is that an actor who already holds a low-privileged foothold in NX-OS can trigger improper neutralization of crafted input that is consumed by a privileged subsystem, yielding high impact to the device's data and control planes. The NVD entry does not identify the specific subsystem, so the analyst should treat that mapping as unresolved pending the vendor advisory.

Exploitation Scenarios

No public PoC is available; the attack chain below is inferred strictly from the vulnerability class (CWE-707) and the CVSS vector. The steps do not assert any specific function, CLI command, API path, or file name, because those are not present in the source data.

1. Reconnaissance / target identification. An attacker locates exposed Cisco NX-OS management interfaces on the network using Shodan or internal asset discovery (NX-OS is typically reachable over management VRF interfaces, SSH, and HTTPS-based management planes). The CVSS AV:N rating means the vulnerable surface is reachable across the network, so exposure enumeration is the natural first step.

2. Prerequisite access. Because PR:L is in the vector, the attacker must already possess a low-privileged credential or session context. This is consistent with an insider threat, a compromised operator account, or a pivot from another compromised system in the management plane. No user interaction (UI:N) is required from a legitimate operator.

3. Triggering the neutralization failure. The attacker sends specially crafted input that the vulnerable NX-OS component fails to neutralize correctly. CWE-707 failures can manifest in several distinct downstream outcomes depending on what consumes the unneutralized data — e.g., injection into a command interpreter, injection into a structured data parser, or bypass of a validation gate. The NVD text does not specify which of these occurs, so the precise payload cannot be reproduced from the advisory alone.

4. Post-exploitation impact. With C:H/I:H/A:H, a successful trigger results in high confidentiality, integrity, and availability impact to the device. In practice that means an attacker who started from a low-privileged context can read sensitive configuration or control-plane state, modify device behavior, and potentially destabilize forwarding or management services. Scope unchanged (S:U) means the impact is contained within the NX-OS component rather than extending to a separate security authority, so a full hypervisor-style escape is not implied by the vector.

Until a vendor advisory enumerating the specific modules and fixed release is published, defenders should assume the affected surface spans any NX-OS subsystem that consumes externally supplied input after authentication.

Impact Assessment

• Business impact: Cisco NX-OS is a data-center-class network operating system. A 8.8-rated flaw with high C/I/A impact that requires only low privileges to reach is a significant insider and lateral-movement risk. An attacker who already holds any operator-level access could escalate the impact to full device trust.
• Affected systems: Any Cisco NX-OS deployment that falls within the (currently unpublished) affected version range. Given that no version matrix is available, operators should treat all NX-OS devices without the relevant hardening release as potentially affected and prioritize inventory.
• Blast radius: The immediate blast radius is the individual switch or fabric member. However, because NX-OS devices often sit at the core of a data center fabric, a compromise of fabric state can cascade to tenants, storage networks, and inter-DC connectivity.
• CVSS subscore interpretation: AV:N (remotely reachable) × AC:L (easy to trigger) × PR:L (requires prior low-privileged foothold) × UI:N (no victim interaction) × S:U (no scope escape) × C:H/I:H/A:H (maximum impact triad).
• EPSS: Not yet scored by FIRST.org. Do not assume a low exploitation likelihood — absence of an EPSS score simply reflects that the scoring pipeline has not produced a value yet.
• CISA KEV: Not listed at time of analysis. No known exploitation in the wild is acknowledged by any tracked source.
• PoC/Exploit: None tracked. No public exploit code, no Nuclei template, and no observed exploitation.

Detection Guidance

Sigma Rule

title: Cisco NX-OS Potential CWE-707 Neutralization Bypass Activity
id: 4d1f4b3a-6e0c-4f2e-9c1a-2b7f0e5c8d91
status: experimental
description: Detects anomalous authenticated management-plane activity on Cisco NX-OS that may correlate with an improperly neutralized input being consumed by a privileged subsystem (CWE-707). This rule is heuristic and should be tuned to local baselines.
references:
  - https://nvd.nist.gov/vuln/detail/CVE-2026-76453
author: valtersit.com
date: 2026/01/01
logsource:
  product: cisco
  service: nxos
detection:
  selection_login:
    action: 'login'
    outcome: 'success'
  selection_anomalous_input:
    message|contains:
      - 'parse error'
      - 'invalid input'
      - 'unexpected token'
      - 'neutralization'
      - 'invalid argument'
  condition: selection_login followed by selection_anomalous_input
falsepositives:
  - Network operators issuing malformed CLI commands during troubleshooting
  - Automated configuration management tools with validation bugs
level: medium
tags:
  - attack.t1190
  - cve.2026.76453
  - cwe.707

YARA Rule

rule CVE_2026_76453_NXOS_Neutralization_Artifacts
{
    meta:
        author = "valtersit.com"
        description = "Heuristic detection of post-exploitation artifacts on Cisco NX-OS management-plane captures or memory dumps potentially associated with CWE-707 neutralization failures aggregated under CVE-2026-76453. Specifics are unavailable; rule is intentionally broad."
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2026-76453"
        date = "2026-01-01"
        severity = "high"

    strings:
        $cve   = "CVE-2026-76453" ascii wide nocase
        $nxos  = "NX-OS" ascii wide nocase
        $mark1 = "improper neutralization" ascii wide nocase
        $mark2 = "CWE-707" ascii wide nocase

    condition:
        uint16(0) != 0x5A4D and
        (
            $cve or
            ($nxos and 2 of ($mark*))
        )
}

Suricata IDS Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2026-76453 Cisco NX-OS Possible Neutralization Bypass - Anomalous Management Traffic"; flow:to_server,established; content:"NX-OS"; nocase; threshold:type both, track by_src, count 5, seconds 60; classtype:attempted-admin; reference:cve,2026-76453; reference:url,nvd.nist.gov/vuln/detail/CVE-2026-76453; metadata:affected_product Cisco_NX-OS, attack_target Networking_Device, deployment Perimeter, signature_severity Major, created_at 2026_01_01, updated_at 2026_01_01; sid:202676453; rev:1;)

Elastic Detection

sequence by host.id with maxspan=5m
  [process where event.action == "start" and process.parent.name : "nxos" ]
  [file where event.action == "creation" and file.name : ("*.log", "*.cfg", "*.txt") and
      process.name : ("admin", "root", "nxos") ]

Splunk SPL Query

index=nxos sourcetype=cisco:nxos
| search ("invalid input" OR "parse error" OR "unexpected token" OR "authentication failed")
| stats count by host, user, src_ip, _time, message
| where count > 3
| sort - _time

Wazuh OSSEC Rule

<group name="cisco,nxos,cve-2026-76453,">
  <rule id="202676" level="10">
    <decoded_as>json</decoded_as>
    <field name="program">nxos</field>
    <match>"invalid input"|"parse error"|"unexpected token"|"improper neutralization"</match>
    <description>CVE-2026-76453: Cisco NX-OS suspected CWE-707 neutralization event - possible exploitation attempt</description>
    <mitre>
      <id>T1190</id>
    </mitre>
    <group>cve_2026_76453,cisco_nxos,</group>
  </rule>
</group>

Mitigation & Patch Guidance

Patch confidence: 0/4 (UNPATCHED — no patch evidence from any tracked source). No vendor-provided fixed version, no OSV package release, and no CISA KEV remediation date are currently available.

1. Immediate mitigations (until a vendor fix is identified):

   • Restrict network reachability to NX-OS management interfaces. Where feasible, place management planes in a dedicated out-of-band VRF and limit access to trusted jump hosts.
   • Enforce least privilege for operator accounts. Because the CVSS vector is PR:L, reducing the population of low-privileged accounts directly reduces the attack surface.
   • Enable detailed command accounting and log forwarding to an external SIEM so that anomalous authenticated activity is retained even if local logs can be manipulated.
   • Treat any NX-OS device without a confirmed fixed release as untrusted for high-value configuration data.

2. Patch / upgrade steps:

   • There is no patch reference in the current dataset. Monitor Cisco's NX-OS security advisories page and the NVD entry for CVE-2026-76453 for a published fixed release and affected version matrix.
   • Once a fixed release is published, stage it in a lab or non-production fabric first, verify the fix against the specific named vulnerabilities in Cisco's advisory, then roll out during a maintenance window with rollback capability.

3. Long-term hardening:

   • Adopt hardware-backed authentication (TACACS+/RADIUS with MFA) for all NX-OS management access.
   • Maintain strict configuration drift detection on the fabric. Bundle-style hardening CVEs frequently imply that previously acceptable inputs are now rejected as malformed — baseline command behavior so operational regressions are visible.
   • Subscribe to Cisco's Product Security Incident Response Team (PSIRT) notifications and integrate Cisco advisories into your vulnerability management pipeline, since this CVE was produced from a proactive review and may be re-issued with a version matrix.

References

• NVD — CVE-2026-76453: https://nvd.nist.gov/vuln/detail/CVE-2026-76453
• Cisco Product Security Advisories and Notices: https://sec.cloudapps.cisco.com/security/center/publicationListing.x
• CWE-707 — Improper Neutralization: https://cwe.mitre.org/data/definitions/707.html
• FIRST EPSS (score not yet assigned for this CVE): https://www.first.org/epss/
• CISA Known Exploited Vulnerabilities catalog (CVE not currently listed): https://www.cisa.gov/known-exploited-vulnerabilities-catalog
• Cisco NX-OS Security Advisories search: https://sec.cloudapps.cisco.com/security/center/publicationListing.x?cpe=Cisco%20NX-OS%20Software