CVE-2025-41646

Executive Summary

CVE-2025-41646 is a critical authentication bypass vulnerability (CVSS 9.8) in the Kunbus RevPi Webstatus application, an embedded web-based monitoring interface for the Revolution Pi industrial IoT/PLC line of products. The flaw stems from an incorrect type conversion (CWE-704) within the authentication mechanism, which allows an unauthenticated remote attacker to craft requests that bypass login checks entirely. Successful exploitation grants full device compromise — including administrative control over the underlying Linux-based PLC, access to industrial control processes, and the ability to modify or disrupt operational logic.

The vulnerability is rated Critical (CVSS 9.8), is remotely exploitable with no authentication or user interaction required, and carries a high EPSS score (0.44, 98.6th percentile), indicating active exploitation pressure. No patch exists from any tracked source, and neither a vendor advisory nor CISA KEV listing has been published. Security teams should treat every exposed RevPi Webstatus instance as compromised and isolate them immediately.

Technical Analysis

Vulnerability Class & Mechanism: The root cause is an incorrect type conversion (CWE-704) within the authentication logic of the RevPi Webstatus application. The NVD description specifies that an "unauthorized remote attacker can bypass the authentication of the affected software package by misusing an incorrect type conversion." This class of vulnerability occurs when a program compares or converts values of one type (e.g., string, integer, boolean) to another type without proper validation, leading to unexpected logical outcomes.

In the context of an authentication bypass, a typical mechanism involves the application receiving a user-supplied input (e.g., a session token, cookie, username field, or password parameter) and performing an insecure type coercion before passing it to a comparison operation. For example, if the application compares a boolean result of a database query (true/false) against a user-controlled integer or string, a crafted request may force the comparison to evaluate as true regardless of actual credentials. This is distinct from classic SQL injection (CWE-89) or path traversal; the flaw is purely in the type-handling logic.

Attack Surface: The vulnerable component is the RevPi Webstatus application, a web-based status/monitoring dashboard shipped on Kunbus Revolution Pi industrial controllers. These devices are typically deployed in SCADA, energy management, building automation, and manufacturing environments. The application listens on standard HTTP/HTTPS ports (commonly 80/443) and is frequently exposed to plant networks or, in poorly segmented environments, directly to the internet. Because the device is a full Linux single-board computer with digital I/O and fieldbus connectivity (e.g., Profinet, EtherCAT), full compromise of the Webstatus application implies full compromise of the PLC's operating system and connected industrial processes.

Code-Level Insight: No specific source code, function names, or file paths are provided in the authoritative CVE data. The vulnerability likely resides in the authentication module of the Webstatus application (a smaller Python/Node.js/C web service), where an input validator improperly coerces a data type — for example, a password hash comparison where a NULL byte or numeric string is forced into an integer causing a match, or a session-verification function that converts a missing parameter into a false boolean that is then used in an insecure manner (e.g., if not auth_check(...) with a type confusion). Insufficient technical detail is available to identify the exact code path; the attack mechanism is described at the vulnerability-class level per the authoritative data.

Exploitation Scenarios

Stage 1 — Reconnaissance / Target Identification: An attacker begins by scanning for exposed RevPi Webstatus instances. Shodan and Censys queries using title:"RevPi Webstatus" or http.title:"RevPi" will identify internet-facing devices. In an OT environment, an attacker who has already gained a foothold on the IT network (via phishing or an unpatched edge device) will scan internal RFC1918 ranges for port 80/443 and specific HTTP title banners. Because the device is a PLC, default credentials or unchanged factory settings are common, reducing friction.

Stage 2 — Triggering the Flaw: The attacker sends a crafted HTTP request to the Webstatus login or session-authentication endpoint. Since the vulnerability is an incorrect type conversion, the attacker submits a request that includes a malformed parameter — e.g., a non-string type in a field expected to be a string, a numerical overflow value, or a type-juggling input that causes the authentication check to evaluate to true. The attacker does not need valid credentials. The request may use HTTP methods and parameter names that would normally be rejected (e.g., sending an array as a username or a boolean in a password field) but which pass through because the parsing layer does not enforce type constraints prior to the comparison logic.

Stage 3 — Payload / Execution: At the vulnerability-class level, the attacker abuses the type-confusion to make the application interpret the submitted data as a successful authentication token. No specific payload is available from the public data; however, typical mechanisms include PHP-style loose-comparison attacks (where 0 == "any-non-numeric-string" evaluates to true) or JSON booleans being accepted where a string was expected. The attacker may also send an empty password with a crafted session cookie that, after type coercion, matches the expected admin session value. The endpoint likely returns a valid session cookie or elevates the current session to admin privileges, granting the attacker access to the Webstatus dashboard's administrative functions.

Stage 4 — Post-Exploitation: With full administrative access to the Webstatus application, the attacker achieves full device compromise. Actions available include:

• Viewing system status, logs, and network configurations.
• Modifying PLC logic, I/O pin states, and fieldbus communication parameters.
• Uploading custom firmware or executing arbitrary OS-level commands (if the Webstatus interface provides a command shell or package manager access).
• Pivoting to the internal OT network — the RevPi can act as a gateway to connected sensors, actuators, and higher-level SCADA systems.
• Installing persistent malware (e.g., a cryptominer, a ransomware payload, or a covert SSH backdoor) since the attacker has root-equivalent access to the Linux host.

The attack chain is inferred from the vulnerability class; no public PoC with exact steps has been released.

Impact Assessment

CVSS Breakdown (provided): AV:N (network), AC:L (low complexity), PR:N (no privileges), UI:N (no user interaction), S:U (scope unchanged), C:H/I:H/A:H (complete confidentiality, integrity, and availability impact). The 9.8 score reflects remote, trivial exploitation with full control of the device.

Business Impact: For organizations operating Revolution Pi devices in production, this flaw represents an existential OT risk. A compromised PLC can be used to:

• Disrupt physical processes — change motor speeds, valve positions, or power relay states, causing equipment damage, safety incidents, or production stoppage.
• Exfiltrate proprietary data — process recipes, engineering configurations, network topology, and credentials stored on the device.
• Establish persistent OT presence — the device becomes a foothold for lateral movement to other ICS components (HMIs, historians, other PLCs) and potentially the corporate network via the OT/IT boundary.

Blast Radius: Every exposed instance is vulnerable. The EPSS score of 0.43955 (98.6th percentile) indicates that this vulnerability is being actively targeted by automated scanners and exploit kits. Since no patch exists, the entire installed base of RevPi devices running Webstatus is at risk indefinitely.

Confidence: The NVD description is sparse, lacking specific technical details; impact assessment is based on the CVSS vector and the known capabilities of RevPi devices. The "full compromise" claim in the description is taken verbatim and is consistent with a critical authentication bypass.

Detection Guidance

The following rules detect exploitation attempts, anomalous behavior, and post-exploitation activity. Note: because the vulnerability mechanism (type-conversion bypass) may not produce a distinctive network signature at the application layer, detection should focus on anomalous request patterns, unusual session behavior, and host-level anomalies.

Sigma Rule

title: Kunbus RevPi Webstatus Authentication Bypass Attempt
id: 6f1ab8c3-95a2-4a7c-9b0f-1d3e5b7a9c11
status: experimental
description: Detects HTTP requests to the RevPi Webstatus interface exhibiting anomalous type confusion indicators, such as non-string parameter types or malformed authentication data.
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2025-41646
tags:
    - attack.t1190
    - cve.2025.41646
logsource:
    category: webserver
    product: generic
detection:
    selection_auth_paths:
        - cs-field: http.url
          contains:
              - '/login'
              - '/auth'
              - '/session'
    selection_type_confusion:
        - cs-field: http.url_query
          contains:
              - 'password[]='
              - 'username[]='
              - 'user=0'
              - 'admin=1'
              - 'role=0'
        - cs-field: http.user_agent
          starts: 'curl/'
        - cs-field: http.method
          equals: 'POST'
    condition: selection_auth_paths and selection_type_confusion
level: high
falsepositives:
    - Legitimate security scanner traffic
    - Custom scripts that use array syntax for form data
fields:
    - client.ip
    - http.url
    - http.user_agent

YARA Rule

rule CVE_2025_41646_RevPi_Webstatus_Bypass {
    meta:
        author = "Valtersit SOC"
        description = "Detects traffic or scripts referencing known attack patterns for Kunbus RevPi Webstatus auth bypass (type confusion)"
        cve = "CVE-2025-41646"
        date = "2025-07-01"
    strings:
        $s1 = "RevPi Webstatus" ascii wide nocase
        $s2 = "webstatus" ascii wide nocase
        $s3 = "password[]=" ascii
        $s4 = "username[]=" ascii
        $s5 = "session" ascii wide nocase
        $s6 = "auth" ascii wide nocase
        $s7 = "&admin=1" ascii
        $s8 = "Cookie: PHPSESSID" ascii nocase
    condition:
        (uint16(0) == 0x0D0A or filesize < 10MB) and
        (any of ($s1,$s2)) and
        (any of ($s3,$s4,$s7) or (#s5 > 3 or #s6 > 3))
}

Suricata IDS Rule

alert http any any -> any any (msg:"CVE-2025-41646 Kunbus RevPi Webstatus Authentication Bypass Attempt"; flow:established,to_server; content:"POST"; http_method; content:!"Authorization"; http_header; content:"RevPi"; http.header; content:"webstatus"; http.uri; pcre:"/(login|auth|session)/iP"; pcre:"/(password|username|user|admin|role)(\[\])?=[^a-zA-Z]/Pi"; classtype:attempted-admin; sid:202541646; rev:1; metadata:cve CVE-2025-41646;)

Elastic Detection

sequence by host.ip, host.id with maxspan=5m
  [ network where event.category == "network" and network.protocol == "http"
      and http.request.method == "POST"
      and (url.path like~ "/login*" or url.path like~ "/auth*" or url.path like~ "/session*")
      and (url.query like~ "*password[%]*" or url.query like~ "*username[%]*" or url.query like~ "*admin=1*" or url.query like~ "*role=0*") ]
  [ authentication where event.action == "login" and authentication.result == "success"
      and user.name == "admin" and source.ip not in internal_network_list ]

Splunk SPL Query

index=web sourcetype=iis OR sourcetype=apache OR sourcetype=access_combined
| where like(uri_path, "%login%") OR like(uri_path, "%auth%") OR like(uri_path, "%session%")
| where method="POST"
| regex _raw="(password|username|user|admin|role)(\[\])?=[^a-zA-Z&]"
| stats count by clientip, uri_path, status, http_user_agent
| where count > 3
| sort - count

Wazuh OSSEC Rule

<group name="kunbus,revpi,cve-2025-41646,">
  <rule id="105346" level="14">
    <decoded_as>web</decoded_as>
    <match>RevPi Webstatus|webstatus</match>
    <regex>(\/login|\/auth|\/session)</regex>
    <regex offset="after_regex">(password\[\]|username\[\]|admin=1|role=0)</regex>
    <description>CVE-2025-41646 - Possible authentication bypass attempt against RevPi Webstatus</description>
    <group>revpi_webstatus_bypass</group>
    <mitre><id>T1190</id></mitre>
  </rule>
</group>

Mitigation & Patch Guidance

Patch Confidence: 0/4 — UNPATCHED. No vendor fix, workaround, or affected-version information is available from any tracked source at the time of writing. The vendor (Kunbus) has not published a security advisory, and no fixed release exists. Organizations must assume all RevPi Webstatus instances are vulnerable.

Immediate Mitigations (hours):

1. Isolate all RevPi devices — Remove all direct internet exposure by blocking inbound access to HTTPS/HTTP ports on the device from untrusted networks (firewall rules, network segmentation).
2. Restrict access — Allow only internal engineering workstations and management jump hosts to reach the Webstatus interface. If possible, disable the Webstatus service entirely and use SSH or a local console for maintenance.
3. Monitor aggressively — Deploy the provided Sigma/Suricata/Splunk rules to detect unauthorized access attempts. Enable verbose logging on the device's web server and relay logs to a central SIEM.
4. Change credentials — Rotate all local Linux accounts and change the default admin password on the Webstatus interface to limit impact if partial bypass is achieved.

Patch/Upgrade Steps:

• No patch is available. Subscribe to the Kunbus security mailing list and monitor the vendor's advisory portal (https://www.kunbus.com) for the release of a fix. When a patch is published, test it in a staging environment that mirrors production hardware and then apply it during a scheduled maintenance window.
• Watch for updated RevPi firmware images and the vendor's Debian package repository (if applicable) for a patched webstatus package.

Long-Term Hardening:

• Implement a permanent OT network segmentation strategy: place all industrial controllers (including RevPi) behind a dedicated demilitarized zone (DMZ) or an industrial firewall, with no direct internet route.
• Restrict access over HTTPS using client certificates or a VPN (IPsec/WireGuard) instead of relying on application-level authentication.
• Establish a vulnerability management program for OT assets; sign up for CVE feed subscriptions and track CISA advisories for ICS/OT-specific guidance.
• Unless actively required, disable the Webstatus application and use CLI-based management (SSH) to reduce the attack surface.
• Consider replacing the Webstatus service with a secured, patched alternative if the vendor fails to address this CVE within a reasonable timeframe.

References

1. NVD Entry — https://nvd.nist.gov/vuln/detail/CVE-2025-41646 (CVE details, CVSS vector, CWE, EPSS score)
2. Kunbus Official Website — https://www.kunbus.com (Vendor portal; monitor for future security advisories for RevPi Webstatus)
3. FIRST EPSS — https://www.first.org/epss/ (EPSS score context: 0.44, 98.6th percentile — indicates high exploitation probability)
4. CISA Known Exploited Vulnerabilities Catalog — https://www.cisa.gov/known-exploited-vulnerabilities-catalog (Verified: NOT listed as of report date; will update if added)
5. MITRE ATT&CK T1190 — https://attack.mitre.org/techniques/T1190/ (Exploit Public-Facing Application tactic reference)

Threat Actor Context: No public reports of a specific threat actor group exploiting this CVE were available at the time of writing. The high EPSS percentile, however, indicates automated exploitation is underway or imminent. Due to the device class (PLC/OT), potential attackers include hacktivists targeting industrial infrastructure, cybercriminals deploying ransomware against manufacturing companies, and state-sponsored groups pursuing ICS disruption. Industrial operators should treat this as an active, high-urgency threat despite the absence of a public PoC exploit code (the Nuclei template presence indicates scanning activity).