CVE-2026-76465

Executive Summary

CVE-2026-76465 is a critical, unauthenticated remote code execution and denial-of-service vulnerability in the MPLS Operations, Administration, and Maintenance (OAM) feature of Cisco NX-OS Software running on Cisco Nexus 3000 and Nexus 9000 Series Switches. An attacker with network reachability to an IP address on an affected device can send a crafted MPLS echo-request packet to trigger improper validation, potentially executing arbitrary code with root privileges and/or causing a device reload. With a CVSS base score of 9.8 (AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H), the vulnerability is trivially exploitable where reachable and carries full confidentiality, integrity, and availability impact; no patch, PoC, or active exploitation evidence is currently available in tracked sources.

Technical Analysis

The vulnerability resides in the MPLS OAM processing path of Cisco NX-OS. MPLS OAM uses echo-request and echo-reply messages (analogous to ICMP echo) to verify label-switched path (LSP) connectivity and to perform path tracing across MPLS domains. Because these messages are network-facing control-plane probes, the receiving stack must rigorously validate packet structure, length fields, and encapsulated payloads before processing.

Per the NVD description, the root cause is improper validation when an affected device processes an MPLS echo-request packet. The CWE assigned is CWE-590: Free of Memory not on the Heap — an invalid free / memory-corruption class. This indicates that malformed echo-request input drives the code into freeing a memory region that was not allocated on the heap (e.g., a stack pointer, a static/global buffer, or an interior pointer), producing undefined behavior that can be weaponized for code execution or crash the process.

Key technical characteristics:

• Attack surface: The MPLS OAM UDP-based echo-request handling path, reachable by any host that can send a packet to an IP address configured on the device (TTL and MPLS label constructs may influence reachability, but the vector is network-remote).
• Authentication requirement: None (PR:N). No session, credential, or prior state is needed.
• Exploit primitive: Memory corruption resulting from an invalid free. Successful exploitation can yield arbitrary code execution with root privileges, meaning full control of the switch's control plane. Failure of exploitation degrades to a crash of the affected process, which the description states can cause a device reload and DoS.
• Complexity: Low (AC:L), no user interaction (UI:N), scope unchanged (S:U).

The precise malformed field(s) within the MPLS echo-request that trigger the invalid free are not disclosed in the available data. No function names, offsets, or code paths are specified by the vendor in the provided description, and none are asserted here.

Exploitation Scenarios

The attack chain below is described at the vulnerability-class level. No public proof-of-concept exists; the chain is inferred from the vulnerability class (invalid free via improper input validation) and the network-facing nature of MPLS OAM.

1. Reconnaissance / target identification. An attacker scans for reachable Cisco Nexus 3000/9000 devices, typically via management or routed data-plane interfaces. Fingerprinting can leverage router/switch banners, SNMP, or the presence of MPLS-enabled services. Shodan and similar internet-scanning services can identify exposed devices via product/version banners.
2. Triggering the flaw. The attacker crafts an MPLS OAM echo-request packet and sends it to an IP address on the affected device. The crafted packet carries a malformed or inconsistent structure that the device fails to validate. Processing of this packet causes the code to attempt to free memory that was not allocated on the heap (CWE-590), corrupting heap/allocator metadata or otherwise inducing undefined behavior.
3. Payload / execution (class-level). Invalid-free conditions are exploitable by manipulating allocator metadata or inducing double-free / overlapping-chunk scenarios; where the freed region overlaps an attacker-influenced allocation, this can be leveraged toward control-flow hijack and ultimately code execution at root. No specific exploitation technique, offset, or payload structure is asserted because none is disclosed. If memory corruption cannot be converted to code execution, the outcome is a process crash.
4. Post-exploitation impact. Because a successful exploit runs with root privileges on the switch OS, impact includes full control over the device's control plane: configuration modification, traffic interception/redirection, and persistence. The description further notes that process crashes from the same flaw can trigger a device reload, producing a DoS condition — impairing all traffic traversing the device. No lateral-movement or campaign-specific tooling is evidenced in the provided data.

Impact Assessment

• CVSS v3.1: 9.8 (CRITICAL) — CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.
• Confidentiality (C:H): Root-level access can expose routing tables, configurations, and any traffic transiting the device.
• Integrity (I:H): An attacker can alter device configuration and control-plane behavior.
• Availability (A:H): Both arbitrary-code execution and crash-driven device reloads can cause complete loss of service on the affected switch.
• Blast radius: Every network segment that depends on a compromised Nexus 3000/9000 switch for connectivity. Switches are typically core/distribution/leaf devices in data-center fabrics; a device reload or takeover can cascade outages across east-west and north-south traffic. Nexus 9000 series (including ACI leaf/spine roles) and Nexus 3000 series are commonly deployed at scale in data-center environments, magnifying systemic exposure.
• Exploitability: PR:N + AC:L + no user interaction means a single unauthenticated packet reaches the vulnerable code path; the only gating factor is network reachability to a device IP address.

Detection Guidance

Detection should focus on anomalous/fragmented MPLS OAM traffic, control-plane integrity events (crashes, reloads, invalid-free symptoms such as malloc/allocator error logs), and unexpected configuration changes. Crafted echo-requests may deviate from legitimate MPLS OAM formats; monitoring for malformed or high-volume UDP OAM traffic is warranted.

Sigma Rule

title: Potential Cisco NX-OS MPLS OAM Echo-Request Exploitation (CVE-2026-76465)
id: 3f9a1c2e-7b44-4d1a-9c6e-2a8b5d1f0e77
status: experimental
description: Detects process crashes, allocator errors, or unexpected reload triggers associated with malformed MPLS echo-request processing on Cisco NX-OS Nexus 3000/9000 switches.
references:
  - https://nvd.nist.gov/vuln/detail/CVE-2026-76465
author: valtersit.com
logsource:
  product: cisco
  service: nxos
detection:
  keywords:
    - 'mpls'
    - 'echo-request'
    - 'oam'
  suspicious_keywords:
    - 'invalid free'
    - 'free(): invalid pointer'
    - 'malloc assertion'
    - 'sanitizer'
    - 'core dump'
    - 'process crash'
    - 'reload reason'
  condition: all of keywords and 1 of suspicious_keywords
falsepositives:
  - Legitimate MPLS OAM operations during maintenance windows
level: high

YARA Rule

rule CVE_2026_76465_Cisco_NXOS_MPLS_OAM_Crash
{
    meta:
        description = "Detects strings indicative of malformed MPLS OAM echo-request handling / invalid-free corruption in Cisco NX-OS memory dumps or logs"
        author = "valtersit.com"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2026-76465"
        date = "2026-01-01"

    strings:
        $mpls_oam = "MPLS OAM" nocase
        $echo_req = "echo-request" nocase
        $cwe590   = "CWE-590" nocase
        $crash1   = "free(): invalid pointer"
        $crash2   = "double free or corruption"
        $reload   = "unexpected reload" nocase

    condition:
        ($mpls_oam or $echo_req) and 1 of ($crash1, $crash2, $reload) or $cwe590
}

Suricata IDS Rule

alert udp any any -> $HOME_NET any (msg:"CVE-2026-76465 Cisco NX-OS MPLS OAM Echo-Request Memory Corruption Attempt"; flow:stateless; content:"|00 01|"; depth:2; byte_test:1,>,0,0,relative; classtype:attempted-admin; reference:cve,2026-76465; sid:202676465; rev:1;)

Note: The above is a baseline signature placeholder; production tuning requires the exact MPLS OAM UDP port and message-type byte values, which are not disclosed in the provided data. Where decoding is available, prefer Suricata's MPLS/eve logging with anomaly-based correlation rather than fixed content matches.

Elastic Detection

event.category: "network" and network.transport: "udp" and
(
  network.protocol: "mpls" or message: "*MPLS*OAM*" or message: "*echo-request*"
)
and not source.ip: ("10.0.0.0/8","172.16.0.0/12","192.168.0.0/16")

Splunk SPL Query

index=network sourcetype=cisco:nxos
| search ("MPLS OAM" OR "echo-request")
| eval abuse_score = case(match(_raw,"(?i)invalid free"),3, match(_raw,"(?i)reload reason.*mpls"),3, match(_raw,"(?i)malloc"),2, true(),1)
| where abuse_score >= 2
| stats count min(_time) as first_seen max(_time) as last_seen by host src
| sort - abuse_score

Wazuh OSSEC Rule

<group name="cisco,nxos,mpls,oam,">
  <rule id="100765" level="12">
    <decoded_as>nxos</decoded_as>
    <match>MPLS OAM|echo-request</match>
    <regex>invalid free|reload reason|malloc|unexpected reload</regex>
    <description>CVE-2026-76465: Possible exploitation of Cisco NX-OS MPLS OAM echo-request processing (memory corruption / crash).</description>
    <mitre>
      <id>T1190</id>
    </mitre>
  </rule>
</group>

Mitigation & Patch Guidance

Patch confidence: 0/4 (UNPATCHED — no patch evidence from any tracked source).

1. Immediate mitigations (until a vendor fix is available):
   • Restrict network reachability to switch management and routed interfaces via control-plane ACLs (CoPP) and infrastructure ACLs; permit only trusted management subnets.
   • Disable MPLS OAM echo functionality or the MPLS feature on devices that do not require it. Since no vendor workarounds are confirmed in the provided data, validate any MPLS OAM CLI restrictions against Cisco documentation before applying.
   • Enforce MPLS TTL propagation / filtering and edge filtering to block crafted label/TTL constructs from untrusted interfaces.
   • Segment management planes in out-of-band (OOB) networks; ensure no internet- or untrusted-segment reachability to device IP addresses.
   • Apply rate limiting on control-plane traffic to reduce DoS and brute-force trigger attempts.
2. Patch / upgrade steps:
   • Monitor Cisco's Security Advisories page and the Cisco NX-OS software download portal for an advisory and fixed release addressing CVE-2026-76465. No advisory or fixed version was present in tracked sources at the time of this report; upgrade promptly once published.
   • Maintain an accurate hardware/software inventory (Nexus 3000 and 9000 models, NX-OS versions) to accelerate patch deployment.
3. Long-term hardening:
   • Adopt proactive lifecycle management: subscribe to Cisco PSIRT notifications and subscribe to CISA's Known Exploited Vulnerabilities (KEV) feed (currently this CVE is NOT listed in KEV).
   • Deploy control-plane protection and continuous configuration/ integrity monitoring; alert on unexpected reloads, core dumps, and allocator errors, which can indicate attempted exploitation.
   • Conduct periodic architecture review to minimize MPLS OAM exposure and reduce the switch control-plane attack surface, and enforce least-privilege access to device management.

References

• NVD — CVE-2026-76465: https://nvd.nist.gov/vuln/detail/CVE-2026-76465
• CWE-590 — Free of Memory not on the Heap: https://cwe.mitre.org/data/definitions/590.html
• Cisco Security Advisories (check for published advisory): https://sec.cloudapps.cisco.com/security/center/publicationListing.x
• CISA Known Exploited Vulnerabilities Catalog (CVE not currently listed): https://www.cisa.gov/known-exploited-vulnerabilities-catalog

No public proof-of-concept, exploit code, Nuclei template, or threat-actor campaign is present in the provided data. No exploit-in-the-wild evidence or KEV association exists as of this report; the exploitation analysis is derived from the vulnerability class (CWE-590) and the vendor description alone.