CVE-2026-89025

Executive Summary

CVE-2026-89025 is a remote, unauthenticated denial-of-service vulnerability in the integrated web server of Hirschmann HiOS Switch Platform devices, caused by missing validation of HTTP(S) content (CWE-755: improper handling of exceptional conditions). A remote attacker can send a specially crafted HTTP(S) request to a specific endpoint that is processed incorrectly, triggering an unintended device reboot and a temporary loss of availability. The vulnerability carries a CVSS v3.1 base score of 7.5 (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H) — a high-severity, network-reachable availability impact requiring no credentials and no user interaction.

Technical Analysis

The affected component is the integrated web server that ships with the Hirschmann HiOS Switch Platform. According to the NVD description, the root cause is "missing validation of HTTP(S) content." This maps to CWE-755, which covers products that do not properly handle or constrain exceptional conditions. In this case, the web server fails to validate inbound HTTP(S) content against expected structure or constraints; a "specially crafted" request "to a specific endpoint" is then "processed incorrectly," causing the device to perform an unintended reboot.

Two elements of the description deserve emphasis for defenders:

1. Attack surface — the management web server. The web server is a network-facing management interface. It is reachable over the network in default deployments (CVSS AV:N), and the request requires no authentication (PR:N) and no user interaction (UI:N). This places the flaw in the classic "management-plane exposed to the data plane" category that repeatedly affects industrial/OT network equipment.

2. Failure mode — unintended reboot, not code execution. The impact vector shown is availability-only (C:N/I:N/A:H). There is no indication in the source data of memory corruption leading to remote code execution, nor of confidentiality or integrity impact. The observable effect is a device restart, which produces a temporary denial of service.

The NVD description does not name the specific endpoint, the HTTP method, the parameter, or the malformed content pattern involved. Because the source material provides no verbatim endpoint path, function name, or parameter name, this report deliberately does not invent them. At the vulnerability-class level, the mechanism is: an HTTP(S) request whose content deviates from what the web server's parser/handler expects is not rejected or safely handled, so the handler enters an undefined/exceptional state. On embedded switch platforms, an unrecovered exception in a management daemon frequently propagates to the platform watchdog or supervisor, which reboots the device to restore a known-good state. That sequence is consistent with the reported "unintended reboot."

CWE-755 is a broad parent category. Its use here, combined with the "missing validation" phrasing, suggests the defect is an input-validation/handling gap rather than a classic memory-safety bug — but no patched-vs-vulnerable code diff is available, so the exact faulty code path cannot be confirmed from the supplied data.

The full set of HiOS branches with a fixed release — 07.1.x, 08.7.x, 09.0.x, 09.3.x, 10.3.x, 10.5.x — indicates the defect is long-lived and shared across several major release trains, consistent with a common web-server codebase reused across hardware generations.

Exploitation Scenarios

No public proof-of-concept, exploit code, or Nuclei template is available for CVE-2026-89025. The following attack chain is therefore inferred from the vulnerability class (unauthenticated input-validation failure in a network-facing web server causing a restart) and from the NVD description; it does not rely on any invented endpoint, parameter, or payload string.

1) Reconnaissance / target identification. An attacker enumerates network-reachable Hirschmann HiOS switches. This can be done by scanning for exposed HTTPS/HTTP management interfaces on OT/industrial networks, or by querying internet-exposure search engines using product/banner fingerprints (see the Shodan dorks in METADATA). Because the flaw is in the integrated web server, any HiOS device with its web management interface reachable from the attacker's position is a candidate. Low-privilege footholds inside an OT VLAN are sufficient — no credentials are required for the attack itself.

2) Triggering the flaw class. The attacker sends a "specially crafted HTTP(S) request" to "a specific endpoint" on the web server. Per the description, the request is not authenticated, and the web server's missing content validation means the malformed request is "processed incorrectly" rather than rejected with a clean error. This is the defining characteristic of a CWE-755 condition: the server does not constrain/handle the exceptional input, and the handler's error path is not safe.

3) Execution / delivery. Delivery is a single network request (or a small number of requests) to the identified endpoint — no file upload, no credentials, no user interaction. At this level of abstraction, the "payload" is a request whose content is outside the bounds the web server expects. The precise structure of that content is not disclosed in the available data and is not fabricated here.

4) Post-exploitation impact. The immediate effect is an unintended device reboot, producing a temporary denial of service. Within the reboot window, the switch's forwarding and management functions are unavailable. Repeated or automated triggering can convert a "temporary" condition into a sustained outage — a plausible availability-denial primitive against a network segment if executed continuously. Notably, the CVSS vector shows no integrity or confidentiality impact, so data disclosure or configuration tampering is not claimed.

Operational caveat. Because no PoC exists and no endpoint is named in the source data, defenders should treat this as an unweaponized-but-trivially-reachable availability flaw: the skill and tooling barrier for an attacker is low (single unauthenticated request), while the public evidence base is thin. Absence of a public exploit does not imply low real-world risk for exposed OT management planes.

Impact Assessment

• CVSS v3.1 base: 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.
• Availability (A:H): The device reboots unexpectedly, causing a temporary denial of service. For a network switch, this can interrupt connectivity for downstream devices, management access, and — in industrial deployments — the OT processes that depend on that segment.
• Confidentiality/Integrity (C:N/I:N): The scored vector indicates no confidentiality or integrity impact. The vulnerability is an availability-only issue.
• Exploitability (AV:N/AC:L/PR:N/UI:N): Remotely exploitable over the network, low complexity, no privileges, no user interaction. This is the most concerning dimension for exposed devices.
• Scope (S:U): Impact is confined to the vulnerable component per the vector.
• Blast radius. Hirschmann HiOS is deployed in industrial/OT networks (manufacturing, energy, transportation, critical infrastructure). A forced reboot of a core or aggregation switch can cascade to dependent segments. Because exploitation is unauthenticated and requires only network reachability to the web management interface, any internet-exposed or cross-VLAN-reachable HiOS device is in scope.
• EPSS. Not yet scored by FIRST.org at the time of writing; no EPSS value is asserted here.
• CISA KEV. Not listed. No evidence of exploitation in the wild from the supplied data.
• Patch confidence: 0/4 (UNPATCHED per tracked sources). Although the vendor description names fixed HiOS versions, no patch artifact was corroborated by any tracked source, so this report treats remediation as vendor-attested only.

Detection Guidance

Sigma Rule

title: Potential Hirschmann HiOS Web Server DoS Request (CVE-2026-89025)
id: 3c9b1f42-7a6e-4d2f-9c11-hios89025d
status: experimental
description: Detects anomalous/unvalidated HTTP(S) requests to Hirschmann HiOS integrated web servers that may trigger CVE-2026-89025. Endpoint is not disclosed; tune to your environment.
references:
  - https://nvd.nist.gov/vuln/detail/CVE-2026-89025
author: Valters IT Threat Intelligence
date: 2026/01/01
logsource:
  category: webserver
  product: hirschmann_hios
detection:
  selection_method:
    cs-method:
      - 'GET'
      - 'POST'
      - 'PUT'
  selection_anomaly:
    # Tune: malformed/oversized/abnormal content to the management web server
    sc-status:
      - 500
      - 0
    cs-uri-query|contains:
      - '%00'
      - '../'
  condition: selection_method and selection_anomaly
falsepositives:
  - Legitimate malformed requests during fuzzing or pen-testing
  - Other vulnerable endpoints
level: medium
tags:
  - attack.t1190
  - cve.2026.89025

YARA Rule

rule CVE_2026_89025_Hirschmann_HiOS_WebDoS_Indicators
{
    meta:
        description = "Heuristic indicator match for CVE-2026-89025 Hirschmann HiOS web-server DoS probing"
        author = "Valters IT Threat Intelligence"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2026-89025"
        date = "2026-01-01"
        cve = "CVE-2026-89025"
    strings:
        $hios1 = "HiOS" ascii nocase
        $hios2 = "Hirschmann" ascii nocase
        $web  = "Server:" ascii nocase
        $m1   = "%00" ascii
        $m2   = "../../" ascii
    condition:
        (uint16(0) == 0x4854 or uint16(0) == 0x5447) and
        any of ($hios*) and $web and any of ($m1, $m2)
}

Suricata IDS Rule

alert http any any -> any any (msg:"CVE-2026-89025 Hirschmann HiOS Suspicious Web Request (potential DoS)"; flow:to_server,established; http.header; content:"Host"; nocase; content:"HiOS"; http.header; nocase; http.uri; content:"%00"; nocase; classtype:attempted-dos; reference:cve,2026-89025; reference:url,nvd.nist.gov/vuln/detail/CVE-2026-89025; sid:9000251; rev:1;)

Elastic Detection

sequence by source.ip with maxspan=10s
  [ network where network.protocol == "http" and
      http.request.method in ("GET","POST","PUT") and
      url.path != null and
      url.path : "*%00*" ]
  [ network where network.protocol == "http" and
      http.response.status_code in (500, 502, 503, 0) ]

Splunk SPL Query

index=web OR index=network sourcetype IN ("hirschmann:hios:web","access_combined","stream:http")
| eval is_hios = if(match(_raw,"(?i)HiOS|Hirschmann"),1,0)
| where is_hios=1
| eval suspicious = if(match(uri,"%00|\.\./") OR status IN (500,502,503,0),1,0)
| where suspicious=1
| stats count min(_time) as first_seen max(_time) as last_seen values(uri) as uris by src_ip, dest_ip, status
| where count >= 1
| convert ctime(first_seen) ctime(last_seen)
| sort - count

Wazuh OSSEC Rule

<group name="hirschmann,hios,web,cve-2026-89025,">
  <rule id="100251" level="10">
    <if_sid>31100</if_sid>
    <match>HiOS|Hirschmann</match>
    <regex>%00|\.\./</regex>
    <description>CVE-2026-89025: Suspicious request to Hirschmann HiOS integrated web server (possible DoS trigger)</description>
    <mitre>
      <id>T1190</id>
    </mitre>
    <options>no_full_log</options>
  </rule>
  <rule id="100252" level="12">
    <if_sid>100251</if_sid>
    <match>reboot|restart</match>
    <description>CVE-2026-89025: HiOS device unexpectedly rebooting following malformed web request</description>
  </rule>
</group>

Mitigation & Patch Guidance

Patch confidence: 0/4 (UNPATCHED — no patch evidence from any tracked source). The vendor-stated fixed releases should be treated as the authoritative remediation target, but no independent patch artifact was corroborated.

1) Immediate mitigations

• Restrict network access to the integrated web server. Place HiOS management interfaces on a dedicated, segmented management VLAN that is not reachable from user, guest, or OT process networks.
• Never expose the HiOS web management interface to the internet. Audit for internet-facing HiOS devices and remove any such exposure.
• Apply ACLs/firewalls so that only authorized administrative hosts (jump hosts, management workstations) can reach the web server port.
• If web management is not required, disable the integrated web server where the platform allows it.
• Monitor device logs for unexpected reboots/restarts and correlate with inbound web requests, since the observable symptom is a reboot.

2) Patch / upgrade steps

• Upgrade to a fixed HiOS release on the appropriate branch: 07.1.12, 08.7.10, 09.0.13, 09.3.03, 10.3.08, or 10.5.00.
• Choose the lowest-risk supported branch that aligns with your hardware and support agreements, and follow the vendor's standard firmware-update procedure (maintenance window; validate configuration backup first).
• Because patch confidence here is 0/4, verify the fix through the vendor's official advisory/portal and confirm release notes explicitly reference this CVE before treating any build as remediated.

3) Long-term hardening

• Adopt an asset inventory for OT/network gear with firmware-version tracking so branch-specific fixes (07.x → 10.5.x) can be scheduled and confirmed.
• Enforce management-plane segmentation as a standing control — availability DoS in switches is far less damaging when the web UI is not broadly reachable.
• Disable unused management services (HTTP, Telnet, etc.) and prefer authenticated, encrypted management paths with strict source restrictions.
• Rate-limit and monitor inbound requests to device web servers; alert on malformed-request spikes and reboot events.
• Track vendor advisories and CISA advisories for Hirschmann/HiOS, and reassess if EPSS rises or the CVE is added to CISA KEV.

References

1. NVD — CVE-2026-89025: https://nvd.nist.gov/vuln/detail/CVE-2026-89025
2. CWE-755: Improper Handling of Exceptional Conditions — https://cwe.mitre.org/data/definitions/755.html
3. Hirschmann / Belden product security advisories (vendor advisory portal — verify the advisory covering HiOS fixed versions 07.1.12, 08.7.10, 09.0.13, 09.3.03, 10.3.08, 10.5.00)
4. CISA Known Exploited Vulnerabilities catalog — https://www.cisa.gov/known-exploited-vulnerabilities-catalog (CVE-2026-89025 is NOT listed at time of writing)
5. FIRST EPSS — https://www.first.org/epss (CVE-2026-89025 not yet scored at time of writing)

Threat actor / exploit-in-the-wild note: No public proof-of-concept (POC_STATUS: None), no Nuclei template, no exploit code, and no CISA KEV entry were identified for CVE-2026-89025 from the available data. No specific threat-actor campaign can be attributed. Given the unauthenticated, low-complexity nature of the flaw and the OT exposure of affected devices, security teams should prioritize management-plane segmentation and firmware verification even absent public exploitation evidence.