CVE-2026-76457

Executive Summary

CVE-2026-76457 is a group of out-of-bounds read vulnerabilities (CWE-125) in Cisco NX-OS, disclosed as part of a proactive internal security review and software hardening release by the Cisco NX-OS engineering team. The flaw is network-reachable, requires no authentication or user interaction, and carries a CVSS 3.1 base score of 8.6 with a scope change and high availability impact. Based on the CVSS vector, successful exploitation is expected to produce a denial-of-service condition against affected NX-OS devices, which typically function as data center switches and are core network infrastructure.

Technical Analysis

The NVD description states that CVE-2026-76457 tracks multiple internally discovered vulnerabilities related to out-of-bounds read issues, grouped under CWE-125. No specific component, process, protocol, or code path is named in the source data, so the analysis must remain at the weakness-class level.

CWE-125 (Out-of-bounds Read) occurs when software reads data past the end or before the beginning of an allocated memory buffer. In network operating systems, such defects commonly arise in packet parsing routines, protocol decoders, or management-plane handlers that process externally supplied input. An out-of-bounds read can cause several outcomes depending on the surrounding memory layout and how the read result is used:

• Crash or process restart if the out-of-bounds access violates a memory boundary and triggers a fault.
• Information disclosure if the over-read data is subsequently returned to the attacker through a response or error message.
• Cascading instability if the affected process is critical to control-plane or data-plane forwarding functions.

The CVSS 3.1 vector supplied for this CVE is AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H. This indicates the following:

• Attack Vector (Network): the vulnerability is remotely reachable over a network.
• Attack Complexity (Low): no specialized conditions or race windows are required.
• Privileges Required (None): no authentication is needed.
• User Interaction (None): no victim action is needed.
• Scope (Changed): exploitation can affect resources beyond the vulnerable component's security authority — consistent with impact spreading from a single affected process to device-wide or adjacent-system availability.
• Confidentiality (None) and Integrity (None): the vector does not claim data theft or modification as a scored impact.
• Availability (High): the primary scored impact is loss of availability, consistent with a denial-of-service or device-reload outcome.

Cisco NX-OS is the operating system for Cisco Nexus data center switches and related platforms. Because the NVD description does not identify the affected subsystem, no specific protocol, daemon, CLI path, or API endpoint can be asserted. The precise attack surface (for example, management interfaces, routing protocol listeners, or data-plane packet handling) is not specified in the available data, and no assumptions should be made about which vector beyond "network-reachable" is involved.

Given the "scope changed" and "availability high" scoring, the most defensible interpretation is that a successful out-of-bounds read destabilizes a critical NX-OS process, potentially leading to a process restart, control-plane disruption, or device reload. However, the exact failure mode cannot be confirmed from the source data alone.

Exploitation Scenarios

No public proof-of-concept, exploit code, or Nuclei template is available for CVE-2026-76457. The following attack chain is inferred at the vulnerability-class level from the NVD description and the CVSS vector, and does not rely on any specific function, endpoint, or parameter, because none are provided in the source data.

1. Reconnaissance and target identification. An adversary identifies reachable Cisco NX-OS devices. Because the attack vector is Network with no privileges or user interaction required, the attacker needs only network reachability to the vulnerable service or interface. Discovery could be performed using standard network scanning and fingerprinting of Cisco NX-OS management or protocol endpoints.

2. Triggering the out-of-bounds read. The attacker sends crafted input to the vulnerable NX-OS component. Because the weakness class is CWE-125, the trigger is input that causes the component to read memory outside the bounds of an allocated buffer. The specific malformed packet, request, or field is not described in the source data, so the exact input cannot be specified. The Low attack complexity and no-authentication requirements indicate that the crafted input can be delivered directly and repeatedly without a valid session or user action.

3. Payload/execution method at the vulnerability-class level. For out-of-bounds reads, the "payload" is typically a specially formed network message, protocol frame, or management request that causes the parser or handler to compute an incorrect length or index and then read beyond the intended buffer. No specific protocol or message format can be named from the available data. The attacker's goal is to force the faulty read and observe the resulting device behavior.

4. Post-exploitation impact. Per the CVSS vector, the scored outcome is High availability impact with scope change, and no confidentiality or integrity impact. This means exploitation is expected to degrade or deny availability — for example, by causing the affected process to crash or the device to become unstable or reload — rather than to exfiltrate data or alter configuration. The scope-change rating suggests the impact can extend beyond the initially affected component. Chaining to further compromise is not supported by the provided data and should not be assumed.

Because no exploit artifacts are public, defenders should treat this as a remotely triggerable availability risk requiring network-exposed NX-OS management and protocol surfaces to be hardened and monitored.

Impact Assessment

CVE-2026-76457 has a CVSS 3.1 base score of 8.6 (High) with the vector CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H. The metric breakdown implies:

• Confidentiality: None. The scored impact does not include data exposure.
• Integrity: None. The scored impact does not include data or configuration modification.
• Availability: High. This is the dominant impact, consistent with denial-of-service, process crash, or device reload.
• Scope: Changed. Effects may propagate beyond the vulnerable component to other resources or systems.

Affected systems are Cisco NX-OS platforms, which are typically deployed as data center switches forming the network core and aggregation layers. The blast radius of an availability-focused flaw on such devices is significant: a reloaded or unstable switch can interrupt east-west traffic, disrupt storage and compute connectivity, and degrade or sever management access. Because the attack requires no authentication and low complexity, any network-reachable attacker (including a compromised host inside the data center) represents a credible threat source.

EPSS has not yet scored this CVE by FIRST.org, and the CVE is not listed in CISA KEV. There is no public PoC, exploit code, or Nuclei template. There is no confirmed evidence of active exploitation in the wild at the time of writing. The patch confidence is 0/4, with no vendor fix or workaround available from tracked sources.

Detection Guidance

Sigma Rule

title: Cisco NX-OS Out-of-Bounds Read Exploitation Attempt (CVE-2026-76457)
id: 8b1f6c2e-3d4a-4f7b-9c1e-7a2d5e6f8b90
status: experimental
description: Detects anomalous process crashes, reloads, or repeated abnormal termination events on Cisco NX-OS devices that may indicate exploitation of CWE-125 out-of-bounds read flaws tracked by CVE-2026-76457.
references:
  - https://nvd.nist.gov/vuln/detail/CVE-2026-76457
author: Valters IT Threat Intelligence
date: 2026/01/01
tags:
  - attack.t1190
  - cve.2026.76457
logsource:
  product: cisco
  service: nx-os
detection:
  selection:
    EventID:
      - 'PROCESS_CRASH'
      - 'PROCESS_RESTART'
      - 'SYSTEM_RELOAD'
    Message|contains:
      - 'out of bounds'
      - 'unexpected restart'
      - 'core dump'
      - 'signal 11'
  condition: selection
falsepositives:
  - Legitimate software upgrades or planned reloads
  - Unrelated hardware faults causing process restarts
level: high

YARA Rule

rule CVE_2026_76457_NXOS_OOB_Read
{
    meta:
        description = "Detects suspicious crash or reload artifacts associated with Cisco NX-OS out-of-bounds read vulnerabilities (CVE-2026-76457)"
        author = "Valters IT Threat Intelligence"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2026-76457"
        cve = "CVE-2026-76457"
        date = "2026-01-01"

    strings:
        $oob1 = "out-of-bounds" ascii nocase
        $oob2 = "out of bounds read" ascii nocase
        $nx1  = "NX-OS" ascii
        $sig1 = "signal 11" ascii nocase
        $sig2 = "segmentation fault" ascii nocase
        $rel1 = "System reload" ascii nocase
        $rel2 = "unexpected reload" ascii nocase

    condition:
        uint16(0) != 0x5A4D and
        (2 of ($oob*) or (1 of ($nx1, $rel1, $rel2) and 1 of ($sig*)))
}

Suricata IDS Rule

alert tcp any any -> any any (msg:"CVE-2026-76457 Possible Cisco NX-OS Out-of-Bounds Read Exploitation Attempt"; flow:to_server,established; threshold: type both, track by_src, count 10, seconds 60; metadata: cve CVE-2026-76457, attack_target Networking_Device, created_at 2026_01_01; classtype:attempted-dos; sid:202676457; rev:1;)

Elastic Detection

sequence by host.name with maxspan=5m
  [any where event.code in ("PROCESS_CRASH","PROCESS_RESTART") and process.name like "*nxos*"]
  [any where event.code in ("PROCESS_RESTART","SYSTEM_RELOAD") and message like "*unexpected*"]

Splunk SPL Query

index=cisco sourcetype="cisco:nxos"
| search ("out of bounds" OR "out-of-bounds" OR "unexpected restart" OR "core dump" OR "signal 11")
| stats count min(_time) as first_seen max(_time) as last_seen by host, process, message
| where count > 3
| sort - count

Wazuh OSSEC Rule

<group name="cisco,nxos,cve-2026-76457,">
  <rule id="100764" level="12">
    <decoded_as>json</decoded_as>
    <field name="program">nxos|kernel</field>
    <match>out of bounds|out-of-bounds read|unexpected restart|core dump|signal 11</match>
    <description>CVE-2026-76457: Possible Cisco NX-OS out-of-bounds read exploitation - process crash or reload detected</description>
    <mitre>
      <id>T1190</id>
    </mitre>
    <group>cve_2026_76457,attempted_dos,</group>
  </rule>
</group>

Mitigation & Patch Guidance

Patch confidence: 0/4 (UNPATCHED — no patch evidence from any tracked source). The CVE states that a software hardening release addresses these issues, but no specific patched NX-OS version is identified in the source data.

1. Immediate mitigations.

   • Restrict network reachability to NX-OS management and protocol interfaces using ACLs, management VRF isolation, and out-of-band management networks.
   • Disable or filter unused protocols and services to reduce the exposed attack surface.
   • Apply rate-limiting and control-plane policing (CoPP) to reduce the feasibility of repeated crafted-input delivery.
   • Enable process crash and reload logging and forward device logs to a SIEM for monitoring.

2. Patch/upgrade steps.

   • Track Cisco's NX-OS software hardening advisories for the specific fixed release addressing CVE-2026-76457.
   • Once a fixed version is published, schedule maintenance-window upgrades after validating compatibility with the existing hardware and configuration.
   • Maintain tested configuration backups prior to upgrade to enable rollback.

3. Long-term hardening.

   • Adopt a vulnerability management process that includes periodic review of Cisco NX-OS security advisories.
   • Segment data center management planes from production traffic.
   • Enforce the principle of least privilege for any network management access.
   • Monitor for anomalous process restarts and reloads as an early indicator of exploitation attempts.

References

• NVD — CVE-2026-76457: https://nvd.nist.gov/vuln/detail/CVE-2026-76457
• CWE-125: Out-of-bounds Read — https://cwe.mitre.org/data/definitions/125.html
• Cisco Security Advisories and Notices — https://sec.cloudapps.cisco.com/security/center/publicationListing.x
• FIRST EPSS — https://www.first.org/epss/ (no score currently published for this CVE)
• CISA Known Exploited Vulnerabilities Catalog — https://www.cisa.gov/known-exploited-vulnerabilities-catalog (CVE-2026-76457 not listed)

No known threat actor campaigns or exploit-in-the-wild evidence are available for CVE-2026-76457 based on the provided intelligence data.