CVE-2026-76656

Executive Summary

CVE-2026-76656 is an unauthenticated remote denial-of-service (DoS) vulnerability in HPE NonStop TCP/IP UTILITIES, classified under CWE-306 (Missing Authentication for Critical Function). Exploitation requires that traceroute be executed under certain conditions, where the absence of authentication controls allows a remote, unauthenticated attacker to disrupt availability. With a CVSS v3.1 base score of 5.3 (AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:N/A:H), the impact is confined to availability; confidentiality and integrity are unaffected. No public proof-of-concept, exploit code, or Nuclei template exists, and the vulnerability remains unpatched as of this report.

Technical Analysis

The vulnerability is rooted in CWE-306 — Missing Authentication for Critical Function. In the HPE NonStop TCP/IP UTILITIES component, a critical function associated with the traceroute utility can be reached without an authentication check. Because authentication is absent at that function boundary, the attacker does not need valid credentials (PR:N) and the attack vector is network-reachable (AV:N).

The NVD description is deliberately sparse and states only that an "unauthenticated remote attacker" can "cause a denial of service when traceroute is executed under certain conditions." Accordingly, the following points are the only defensible technical claims:

• Vulnerability class: Missing authentication for a critical function (CWE-306) combined with an availability-impacting fault that manifests during traceroute execution.
• Attack surface: The traceroute functionality exposed by HPE NonStop TCP/IP UTILITIES. This class of utility is typically reachable over the network, consistent with the AV:N vector.
• Preconditions: The exploitability metrics are AC:H (High attack complexity) and UI:R (Required user interaction). This indicates that the attacker cannot reliably trigger the condition at will; it depends on a specific state or condition associated with traceroute execution, and some form of user or operator action is required on the target side.
• Impact scope: C:N/I:N/A:H — availability only. The flaw does not expose or modify data, but can render the affected service or utility unavailable.

No further code-level detail (specific function names, call paths, packet structures, or parameter names) is provided in the source data. Claims about the precise memory-safety or protocol-handling origin of the DoS would be speculative and are therefore excluded. What can be stated with confidence is that the combination of AC:H and UI:R distinguishes this from a trivially scriptable flood attack: it is a conditional fault triggered through the traceroute path, not a simple volumetric DoS.

The absence of any affected version range, OSV package mapping, or vendor fix reference means defenders cannot currently scope exposure by version number and must instead scope by deployed product presence.

Exploitation Scenarios

No public PoC is available; the attack chain below is inferred strictly from the vulnerability class (CWE-306) and the NVD description. No specific function names, endpoints, file paths, or parameters are known, and none are invented here.

1. Reconnaissance / target identification. An attacker identifies internet- or network-reachable HPE NonStop systems running TCP/IP UTILITIES. Fingerprinting focuses on detecting NonStop hosts and confirming that the TCP/IP UTILITIES component — and its traceroute functionality — is present and reachable. Because the CVSS vector is AV:N, the attacker need not have local access.

2. Triggering the flaw class. Exploitation begins with the missing authentication condition: the critical function associated with traceroute does not enforce an authentication check, so an unauthenticated remote actor can interact with it (PR:N). The attacker then drives the traceroute execution path into the "certain conditions" referenced by the NVD. The AC:H metric indicates these conditions are not trivially satisfiable and may depend on timing, target state, or specific invocation characteristics.

3. Execution method (class level). The attacker sends crafted network input intended to reach the unauthenticated critical function while the target is executing traceroute. Because UI:R is present, successful triggering also depends on a user or operator action on the target side — for example, someone invoking or operating the traceroute utility while the attack input is in flight. The attacker does not need credentials, only the ability to reach the service and the coincidence of the required condition.

4. Post-exploitation impact. The realized effect is denial of service: the affected utility or its associated service becomes unavailable (A:H). There is no evidence of confidentiality or integrity loss (C:N/I:N). The attacker gains no code execution, no data access, and no persistence based on the provided data. The attack is therefore disruptive rather than intrusive.

Because no PoC exists, real-world exploitability is limited to actors who can independently reverse the traceroute-related condition. The high attack complexity and required user interaction further constrain mass exploitation.

Impact Assessment

The CVSS v3.1 base score is 5.3 (Medium) with vector CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:N/A:H.

• Exploitability subscores: Network attack vector (AV:N) means the flaw is reachable remotely; PR:N means no privileges are required, widening the pool of potential attackers. These factors are offset by AC:H (conditions must align for successful triggering) and UI:R (a user/operator action is required on the target side), which substantially reduce practical exploitability.
• Impact subscores: Availability is rated High (A:H), while confidentiality and integrity are None. The scope is Unchanged (S:U), meaning the impact is contained within the vulnerable component rather than crossing a security boundary.
• Blast radius: Systems running HPE NonStop with TCP/IP UTILITIES are potentially affected. Because no affected version range is published, the exposed population cannot be precisely enumerated; any deployment where the traceroute functionality is network-reachable should be treated as candidate exposure.
• Business impact: Disruption of traceroute and the surrounding TCP/IP UTILITIES service can impair network diagnostics and monitoring on NonStop systems. In environments where NonStop platforms support transaction processing or other critical workloads, loss of network utilities can degrade operational visibility and troubleshooting during incidents, though the CVSS subscores indicate the core availability impact is to the utility/service rather than the entire host.

No evidence of active exploitation, threat actor campaigns, or CISA KEV listing is present in the provided data. EPSS has not been scored by FIRST.org; no EPSS value is asserted here.

Detection Guidance

Detection must focus on anomalous interaction with HPE NonStop TCP/IP UTILITIES and traceroute-related activity, since no exploit artifacts or signatures are published. The rules below are heuristic and should be tuned to the environment.

Sigma Rule

title: Potential HPE NonStop TCP/IP UTILITIES Traceroute DoS Attempt
id: 8f2c1a44-7665-4656-9a01-hpe76656nsk
status: experimental
description: Detects anomalous or repeated invocation/abuse of traceroute-related functionality on HPE NonStop hosts, consistent with attempts to trigger CVE-2026-76656 (unauthenticated DoS via traceroute under certain conditions).
references:
  - https://nvd.nist.gov/vuln/detail/CVE-2026-76656
author: valtersit.com
date: 2026-01-01
tags:
  - attack.t1499
  - cve.2026.76656
logsource:
  category: process_creation
  product: linux
detection:
  selection_binary:
    Image|endswith:
      - '/traceroute'
      - '/tracert'
  selection_path:
    CommandLine|contains:
      - 'traceroute'
  condition: selection_binary or selection_path
falsepositives:
  - Legitimate network diagnostics and troubleshooting by administrators
  - Scheduled monitoring jobs invoking traceroute
level: low

YARA Rule

rule CVE_2026_76656_HPE_NonStop_Traceroute_DoS_Artifacts
{
    meta:
        description = "Heuristic detection for artifacts or scripts referencing HPE NonStop TCP/IP UTILITIES traceroute abuse (CVE-2026-76656)"
        author = "valtersit.com"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2026-76656"
        date = "2026-01-01"
        severity = "medium"

    strings:
        $s1 = "NonStop TCP/IP UTILITIES" ascii nocase
        $s2 = "traceroute" ascii nocase
        $s3 = "HPE NonStop" ascii nocase
        $cve = "CVE-2026-76656" ascii nocase

    condition:
        uint16(0) == 0x5A4D or uint32(0) == 0x464C457F or $cve or
        (2 of ($s1, $s2, $s3))
}

Suricata IDS Rule

alert tcp any any -> $HOME_NET any (msg:"CVE-2026-76656 Potential HPE NonStop TCP/IP UTILITIES DoS via traceroute"; flow:to_server,established; content:"traceroute"; nocase; threshold: type both, track by_src, count 10, seconds 30; classtype:attempted-dos; reference:cve,2026-76656; reference:url,nvd.nist.gov/vuln/detail/CVE-2026-76656; sid:202676656; rev:1; metadata:created_at 2026_01_01, updated_at 2026_01_01;)

Note: no protocol-level exploit signature is published for this CVE. This rule is a heuristic that flags elevated traceroute-related traffic volume; byte-level accuracy cannot be guaranteed without a PoC.

Elastic Detection

sequence by host.id, process.parent.pid with maxspan=30s
  [process where process.name in ("traceroute","tracert")]
  [network where network.direction == "inbound" and network.transport == "tcp"]

Heuristic correlation: a traceroute invocation followed closely by inbound TCP traffic on the affected host may indicate the specific conditions required to trigger CVE-2026-76656. Tune thresholds to baseline.

Splunk SPL Query

index=os OR index=main sourcetype IN ("linux_secure","syslog","Sysmon")
| search (ProcessName="traceroute" OR CommandLine="*traceroute*" OR Message="*NonStop*")
| stats count min(_time) as first_seen max(_time) as last_seen by host, user, ProcessName, CommandLine
| where count > 5
| convert ctime(first_seen) ctime(last_seen)
| sort - count

Adjust index/sourcetype to match the environment. Alert on hosts where traceroute-related activity spikes relative to baseline, or where it coincides with unexpected inbound connections.

Wazuh OSSEC Rule

<group name="hpe_nonstop,cve_2026_76656,">
  <rule id="202676656" level="7">
    <decoded_as>syslog</decoded_as>
    <match>traceroute</match>
    <description>CVE-2026-76656: Possible HPE NonStop TCP/IP UTILITIES traceroute DoS activity detected.</description>
    <mitre>
      <id>T1499</id>
    </mitre>
    <group>dos,</group>
  </rule>
</group>

Deployable on the Wazuh manager to correlate syslog entries referencing traceroute on monitored NonStop-adjacent hosts. Tune level and thresholds to local policy.

Mitigation & Patch Guidance

Patch confidence: 0/4 — UNPATCHED. No patch evidence exists from any tracked source; no vendor fix, workaround, or affected version range has been published in the provided data.

1. Immediate mitigations:

   • Restrict network reachability of HPE NonStop TCP/IP UTILITIES and any traceroute-related functionality to trusted management networks via firewall/ACL or network segmentation. Because the flaw is AV:N and PR:N, reducing reachability is the most effective compensating control.
   • Enforce authentication and access control at the network boundary in front of the affected utility, compensating for the missing authentication (CWE-306) at the function level.
   • Limit who can invoke traceroute on affected systems and monitor for unexpected invocations, given the UI:R requirement.
   • Because the issue is availability-only, prepare operational continuity measures (monitoring, alerting, alternate diagnostic tooling) so loss of the utility does not blind network operations.

2. Patch/upgrade steps:

   • No patch is currently available. Monitor HPE security bulletins and the vendor advisory for HPE NonStop TCP/IP UTILITIES for a fixed release, and track the NVD entry for updates.
   • When a vendor fix is released, validate it against a non-production NonStop system, then schedule deployment during a maintenance window. Maintain an inventory of NonStop systems running TCP/IP UTILITIES so patching can proceed quickly.

3. Long-term hardening:

   • Apply a deny-by-default network posture for management and diagnostic utilities; do not expose traceroute or TCP/IP UTILITIES to untrusted networks.
   • Enforce authentication on critical functions as a design principle (addresses CWE-306 root cause) and review other utilities for analogous missing-authentication conditions.
   • Reduce reliance on a single diagnostic utility by deploying redundant, separately-segmented network monitoring.
   • Continuous monitoring: baseline traceroute usage, alert on anomalies, and subscribe to HPE and CISA advisories for NonStop product security.

References

• NVD — CVE-2026-76656: https://nvd.nist.gov/vuln/detail/CVE-2026-76656
• CWE-306 — Missing Authentication for Critical Function: https://cwe.mitre.org/data/definitions/306.html
• MITRE ATT&CK — T1499 Endpoint Denial of Service: https://attack.mitre.org/techniques/T1499/
• FIRST — EPSS (not yet scored for this CVE): https://www.first.org/epss/
• CISA Known Exploited Vulnerabilities Catalog (CVE-2026-76656 not currently listed per provided data): https://www.cisa.gov/known-exploited-vulnerabilities-catalog
• HPE Security Bulletins / Product Security: https://support.hpe.com/ (monitor for NonStop TCP/IP UTILITIES advisory)

No threat actor campaigns, exploit-in-the-wild evidence, or public PoC have been identified for CVE-2026-76656 in the provided data.