CVE-2026-111855

Executive Summary

CVE-2026-111855 is a path traversal (CWE-22) vulnerability in the web management interface of Tektronix 3 Series MDO mixed-domain oscilloscopes running firmware before 1.21.1. Insufficient validation of user-supplied file paths allows remote attackers to read arbitrary files accessible to the web application, and depending on configuration, exploitation may be possible without authentication (CVSS 7.5, network-accessible, high confidentiality impact). Devices exposed to untrusted networks—lab benches, engineering VLANs, or internet-facing management ports—are at risk of configuration and credential disclosure.

Technical Analysis

The vulnerability resides in the device's embedded web management interface. Per the NVD description, the interface fails to adequately validate user-supplied file paths, enabling directory traversal so that a remote attacker can cause the application to read files outside its intended document root or designated directory. This is a classic CWE-22 "Improper Limitation of a Pathname to a Restricted Directory" weakness: path input reaches a filesystem operation without canonicalization and containment checks, allowing sequences that resolve outside the intended base path to reach files the web service process can access.

Key characteristics derivable from the supplied data:

• Attack vector: Network (AV:N). The web management interface must be reachable over the network.
• Attack complexity: Low (AC:L). The flaw is a well-understood class; no specialized conditions are described.
• Privileges required: None (PR:N). The description explicitly states exploitation "may be possible without authentication" depending on configuration, meaning exposed deployments may be exploitable pre-auth.
• User interaction: None (UI:N).
• Scope: Unchanged (S:U); impact is confined to the vulnerable application.
• Confidentiality impact: High (C:H). Arbitrary file read can expose device configuration, stored credentials, certificates, logs, and any other file the web process may read. Integrity and availability impacts are None.

Because the CNA title and description provide no endpoint names, parameter names, or function-level detail, the precise request structure, traversal encoding (e.g., ../ sequences, encoded or normalized variants), and targeted paths cannot be specified here and are not asserted. No public proof-of-concept, Nuclei template, or exploit code is known from the tracked sources.

Exploitation Scenarios

No public PoC is available; the attack chain below is inferred from the vulnerability class (file-read path traversal in an embedded web interface) and the CVSS metadata, not from published exploit artifacts.

1. Reconnaissance / target identification. An attacker scans for reachable Tektronix 3 Series MDO devices by identifying the web management interface on the exposed management port (network-accessible per AV:N). Device fingerprinting can leverage HTTP response banners, page titles, or the presence of the management UI.

2. Triggering the flaw class. The attacker sends crafted HTTP requests to the web management interface in which a file-path value supplied to the application is manipulated using traversal sequences, intending to make the file operation resolve to a path outside its intended directory. Because the description notes authentication may not be required depending on configuration, the attacker may reach this step without valid credentials.

3. Payload/execution method (class level). Successful traversal causes the application to return the contents of a targeted file to the attacker. No specific URL path, parameter, or file is documented, so exact request construction is not specified here.

4. Post-exploitation impact. Read access yields disclosure of files accessible to the web process—potentially configuration data, credentials, and certificates—which can support follow-on access to the device and adjacent engineering networks. There is no integrity or availability impact per CVSS (I:N/A:N); this is a disclosure-only primitive.

Impact Assessment

CVSS 3.1 base score 7.5 (High): AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N. The vulnerability is a high-confidentiality information-disclosure issue. Affected systems are Tektronix 3 Series MDO oscilloscopes running firmware before 1.21.1 that expose the web management interface. Blast radius depends on network placement: internet-facing or broadly reachable management interfaces create the largest exposure; isolated lab networks reduce it. The absence of authentication requirements (per configuration) lowers the bar for exploitation. Because file contents can include credentials and configuration, downstream risk extends to credential reuse and lateral movement into engineering or OT-adjacent segments, even though the CVSS scope is unchanged. CISA KEV status is NO and EPSS is unscored, indicating no confirmed in-the-wild exploitation evidence in the tracked data at time of writing.

Detection Guidance

Sigma Rule

title: Tektronix 3 Series MDO Web Interface Path Traversal Attempt
id: 8f3c2a71-1b4e-4c9d-9a2e-tektronix-mdo-cve
status: experimental
description: Detects HTTP requests to Tektronix 3 Series MDO web management interface containing path traversal sequences indicative of CVE-2026-111855.
references:
  - https://nvd.nist.gov/vuln/detail/CVE-2026-111855
author: valtersit.com
logsource:
  category: webserver
detection:
  selection_path:
    cs-uri-query|contains:
      - '../'
      - '..%2f'
      - '..%5c'
      - '%2e%2e%2f'
      - '%2e%2e/'
      - '....//'
  selection_host:
    cs-host|contains: 'tektronix'
  condition: selection_path
  falsepositives:
    - Legitimate administrative uploads or diagnostics containing encoded dots
  level: high

YARA Rule

rule CVE_2026_111855_Tektronix_MDO_PathTraversal
{
    meta:
        description = "Detects HTTP request payloads targeting Tektronix 3 Series MDO web interface path traversal (CVE-2026-111855)"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2026-111855"
        author = "valtersit.com"
        severity = "high"
    strings:
        $trav1 = "../" ascii nocase
        $trav2 = "..%2f" ascii nocase
        $trav3 = "%2e%2e%2f" ascii nocase
        $trav4 = "..%5c" ascii nocase
        $dev1  = "Tektronix" ascii nocase
        $dev2  = "MDO" ascii nocase
    condition:
        uint16(0) == 0x4854 and
        2 of ($trav*) and 1 of ($dev*)
}

Suricata IDS Rule

alert http any any -> any any (msg:"CVE-2026-111855 Tektronix 3 Series MDO Path Traversal Attempt"; flow:established,to_server; http.method; content:"GET"; http.uri; content:"../"; nocase; fast_pattern; classtype:web-application-attack; reference:cve,2026-111855; sid:2026111855; rev:1;)

Elastic Detection

sequence by source.ip with maxspan=30s
  [network where http.request.method == "GET" and url.path : "*../*"]
  [network where http.request.method == "GET" and url.path : "*%2e%2e%2f*"]

Splunk SPL Query

index=web OR index=proxy
| eval uri=coalesce(uri_path, url, cs_uri_stem, request)
| where match(uri, "(?i)(\.\./|\.\.%2f|%2e%2e%2f|\.\.%5c|%2e%2e/)")
| stats count min(_time) as first_seen max(_time) as last_seen values(uri) as sample_uris by src_ip, dest_host
| where count > 0
| sort - count

Wazuh OSSEC Rule

<group name="web,attack,">
  <rule id="111855" level="10">
    <if_sid>31100,31103,31108</if_sid>
    <match>\.\./|\.\.%2f|%2e%2e%2f|%2e%2e/|\.\.%5c</match>
    <description>CVE-2026-111855: Possible Tektronix 3 Series MDO web interface path traversal attempt</description>
    <mitre>
      <id>T1190</id>
    </mitre>
    <group>web_scan,</group>
  </rule>
</group>

Mitigation & Patch Guidance

Patch confidence: 0/4 (UNPATCHED — no vendor advisory, commit, or patch source available in tracked data; the NVD description references firmware 1.21.1 as the fixed version).

1. Immediate mitigations

   • Restrict network access to the device web management interface to trusted administrative networks only; block from the internet and general user VLANs via firewall/ACL rules.
   • Where the interface is not required, disable the web management service on the device.
   • Enforce authenticated access and least privilege for management, and monitor for unauthenticated access attempts (per configured behavior).
   • Place devices on segmented engineering/OT networks with egress and ingress filtering.

2. Patch/upgrade steps

   • Upgrade Tektronix 3 Series MDO firmware to 1.21.1 or later as referenced in the NVD description.
   • Verify version post-upgrade and validate management interface behavior. Since no vendor advisory is in tracked data, confirm fix specifics directly with Tektronix.

3. Long-term hardening

   • Inventory all Tektronix and similar lab/OT devices and track firmware versions against the 1.21.1 baseline.
   • Apply a no-internet-exposure policy for test equipment management services.
   • Rotate any credentials, keys, or certificates that could reside on device filesystems, given disclosure risk.
   • Deploy the detection content above to catch traversal probing at perimeter and segment boundaries.

References

• NVD — CVE-2026-111855: https://nvd.nist.gov/vuln/detail/CVE-2026-111855
• CWE-22: Improper Limitation of a Pathname to a Restricted Directory: https://cwe.mitre.org/data/definitions/22.html
• MITRE ATT&CK T1190 — Exploit Public-Facing Application: https://attack.mitre.org/techniques/T1190/
• CISA KEV Catalog (CVE-2026-111855 not listed): https://www.cisa.gov/known-exploited-vulnerabilities-catalog

No known threat actor campaigns or exploit-in-the-wild evidence are associated with this CVE in the tracked data; CISA KEV status is NO and no public PoC, exploit code, or EPSS score is available.