CVE-2026-61886

Executive Summary

CVE-2026-61886 discloses a plaintext password storage vulnerability in the Weintek cMT3092X Human-Machine Interface (HMI). User account credentials are stored unencrypted in the device's filesystem, allowing any authenticated user with filesystem access — or an attacker who has achieved foothold via another vulnerability — to extract valid credentials for all user accounts, including potentially administrator accounts. The CVSS score is 6.5 (High complexity: low privilege requirement enabled via network attack vector), and while no public exploit exists as of this report, the vulnerability class (CWE-256) is well-understood and trivially exploitable once access is gained.

Technical Analysis

The Weintek cMT3092X HMI runs on a Linux-based embedded platform and provides web-based configuration and monitoring via the EasyWeb interface. User accounts are defined locally on the device to control access to HMI screens, alarm management, and system configuration.

The vulnerability lies in the authentication back-end. Weintek's implementation stores user account data in a flat-file configuration database (typically under /usr/etc/ or similar system directory) where the password field is written directly as ASCII text, with no hashing, salting, or encryption. The password appears verbatim in the file, readable by any process or user with filesystem read access on the device.

Attack surface assessment:

• Local filesystem access (SSH, serial console) — a user with even the lowest privilege (e.g., guest account or a limited service account) can read the password file and escalate to admin.
• Remote exploitation — the attacker must first obtain a foothold via another vulnerability (e.g., command injection, default credentials on the web interface) or physical access. Once any code execution is achieved, reading the password file is trivial.
• Backup files — HMI project backup files (.mtx or exported configuration files) may also contain the same plaintext credentials, extending the attack surface to any system that stores these backups.

The code-level issue is straightforward: the software calls a write routine (likely fprintf or write()) to serialise the user object with the password field passed as a raw string. No crypt(), bcrypt, or SHA-2 hashing is applied at rest. The design decision is likely for convenience during factory reset or backup/restore, but it fatally compromises credential confidentiality.

Exploitation Scenarios

While no public PoC exists, the following is the concrete attack chain based on the vulnerability class:

Scenario 1: Local privilege escalation via SSH

1. Reconnaissance: Attacker identifies a cMT3092X HMI on the network (Shodan query http.title:"EasyWeb"). They attempt default credentials — Weintek HMIs often ship with user admin password admin or no password. If successful over SSH (port 22/tcp, which Weintek HMIs commonly expose), they get a low-privilege shell.
2. Trigger: Attacker enumerates the filesystem: find / -name "*.db" -o -name "*.cfg" -o -name "*user*" 2>/dev/null. They locate the user database file (e.g., /usr/etc/user.cfg or /root/.config/users.txt).
3. Weaponization: cat /usr/etc/user.cfg — the file shows lines like username=admin password=Admin@123 in plaintext.
4. Execution: Attacker uses the harvested admin password to log into the EasyWeb web interface with full privileges.
5. Post-exploitation: With admin web access, the attacker can: modify HMI screens to inject malicious ladder logic, change alarm thresholds to disable safety alarms, alter recipe parameters causing product quality issues, and exfiltrate production data. On the HMI itself, they can gain root shell (if admin maps to root) and pivot to the OT network.

Scenario 2: Backup file exfiltration

1. Reconnaissance: Attacker gains any level of access to a workstation that stores Weintek project backup files (.mtx).
2. Trigger: Attacker copies the .mtx file and opens it with a text editor or a simple extraction tool (the format is ZIP-like).
3. Weaponization: The attacker extracts the embedded user database file and reads plaintext passwords.
4. Execution: Using the admin password, the attacker connects to the HMI via EasyWeb from their own machine.
5. Post-exploitation: Attacker plants malicious screen logic that will display false status to operators while concealing an ongoing cyber-physical attack (e.g., manipulating tank levels or temperature readings).

Scenario 3: Chained with network exposure

1. If the EasyWeb service (port 80/tcp) is directly reachable from the corporate network or internet, an attacker can first exploit a web vulnerability (e.g., command injection, if one exists in EasyWeb) to get a shell, then immediately read the password file — bypassing the need for SSH default credentials.

Impact Assessment

• CVSS breakdown: Base score 6.5, vector AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N. The attack vector is network (AV:N), complexity is low (AC:L), requires low privileges (PR:L), no user interaction (UI:N), and no scope change (S:U). The impact is high confidentiality (C:H) with no integrity or availability impact (I:N/A:N).
• Business impact: Weintek HMIs are used extensively in manufacturing, water treatment, energy, and building automation. Credential compromise of an HMI admin account enables an attacker to:
  • View and modify production parameters (integrity loss in the physical process).
  • Disable alarms, masking dangerous conditions.
  • Extract process data (intellectual property loss).
  • Use the HMI as a pivot point deeper into the OT network (OT-specific lateral movement).
• Affected systems: Weintek cMT3092X only (per CNA). Other cMT series models (cMT3072, cMT3151, etc.) are suspected but not confirmed affected.
• Blast radius: The plaintext credential file on the device is readable by any local user. If SSH defaults are weak, this effectively enables remote credential extraction. The backup file vector extends the blast radius to any PC that stores project backups.

Detection Guidance

Sigma Rule

title: Weintek cMT3092X Backup File with Plaintext Passwords
id: 6f2b1c68-0e5f-4d7e-9f4d-2c5e8a1b3f0a
status: experimental
description: Detects the creation or download of a Weintek backup ($MTX) file that contains plaintext password entries.
logsource:
  product: windows
  category: file_event
detection:
  selection:
    TargetFilename|endswith: '.mtx'
  condition: selection
level: medium
falsepositives:
  - Legitimate backup operations by engineering staff
tags:
  - attack.collection
  - attack.t1003

YARA Rule

rule weintek_cmt3092x_plaintext_password
{
    meta:
        author = "Valters IT Security Research"
        description = "Detects Weintek user database content with plaintext passwords"
        cve = "CVE-2026-61886"
        date = "2026-04-15"

    strings:
        $user_tag = "username=" ascii
        $pass_tag = "password=" ascii
        $root_tag = "admin" ascii fullword

    condition:
        uint16(0) == 0x4D5A and
        $user_tag and
        $pass_tag and
        #pass_tag > 2
}

Suricata IDS Rule

alert http any any -> any any (msg:"Weintek EasyWeb - HTTP response containing plaintext user credentials"; content:"/usr/etc/"; nocase; content:"password="; nocase; flow:to_client,established; classtype:attempted-user; sid:202661886; rev:1;)

Elastic Detection

event.category: file AND
event.action: (rename OR write) AND
file.extension: mtx AND
file.name: (*.mtx) AND
NOT process.name: (explorer.exe OR winzip.exe)

Splunk SPL Query

index=filesystems sourcetype="xmlwineventlog:security"
| where EventCode=4663 AND ObjectName LIKE "%.mtx"
| search NOT Image="C:\\Program Files\\Weintek*"
| table _time, Computer, User, ObjectName, SubjectUserName
| sort - _time

Wazuh OSSEC Rule

<group name="weintek,">
  <rule id="100090" level="10">
    <if_sid>550</if_sid>
    <field name="file">\.mtx$</field>
    <description>Weintek backup file (.mtx) created or modified - potential credential exfiltration</description>
    <group>credential_access,</group>
  </rule>
</group>

Mitigation & Patch Guidance

Patch confidence: 2/4 (CLAIMED) — only the CNA claims a patch exists; independent verification is required.

1. Immediate mitigations:

   • Restrict SSH access to the HMI to a management VLAN or firewall rules (allow only from engineering workstations).
   • Change default passwords on all cMT3092X units immediately and use unique strong passwords.
   • Disable or restrict remote SSH/console access if not strictly necessary.
   • Do not store .mtx backup files on shared drives or unencrypted endpoints; if stored, encrypt them with EFS/BitLocker/FileVault.
   • Restrict physical access to the device (serial console port).

2. Patch/upgrade steps:

   • Request the patch package cmt_typeB_20260316_007.patch from Weintek support (https://www.weintek.com/globalw/Support/Knowledge.aspx) or from an authorized distributor.
   • Apply the patch. Note: this is a patch-only update; there is no separate standard firmware release. Do not wait for a full firmware cycle.
   • After applying, verify the EasyWeb version reports as 2.3.17-typeb.
   • Validate that the fix requires a password change for all accounts per the vendor advisory (if provided).

3. Long-term hardening:

   • Segment HMI devices from the corporate IT network; place them in a dedicated OT DMZ.
   • Deploy network monitoring on the OT segment to flag unapproved SSH or web sessions to HMIs.
   • Establish a credential management policy for OT devices: rotate passwords quarterly, use a password manager.
   • Implement a vulnerability management process for ICS/OT devices, tracking CVEs and patch status.
   • If the vendor does not release a timely fix for other cMT models, consider compensating controls (application whitelisting, file integrity monitoring on the HMI filesystem).

References

1. NVD Entry — https://nvd.nist.gov/vuln/detail/CVE-2026-61886
2. Weintek Support Portal (patch request) — https://www.weintek.com/globalw/Support/Knowledge.aspx
3. MITRE ATT&CK — OS Credential Dumping (T1003) — https://attack.mitre.org/techniques/T1003/
4. CISA Known Exploited Vulnerabilities Catalog — https://www.cisa.gov/known-exploited-vulnerabilities-catalog (CVE-2026-61886 NOT listed, as of 2026-04-15)

Threat activity: No known threat actor campaigns or exploit-in-the-wild evidence for CVE-2026-61886 as of this report. However, ICS-CERT advisories note that Weintek HMI devices are popular targets for state-sponsored actors due to their remote access capabilities and manufacturing sector penetration. The plaintext password exposure may have been known to actors before public disclosure, given the CNA's initial disclosure and the patch timeline.