CVE-2024-27767

Executive Summary

CVE-2024-27766 is an improper authentication vulnerability affecting Unitronics UniStream series programmable logic controllers (PLCs) that run Unilogic software versions prior to 1.35.227. The vulnerability, cataloged under CWE-287 (Improper Authentication), may allow a remote, unauthenticated attacker to bypass authentication mechanisms entirely and gain unauthorized access to the controller. Given a CVSS score of 10.0 — the maximum severity rating — combined with network-based attack vector, no privileges required, and no user interaction, this vulnerability represents a critical risk to industrial control system (ICS) environments that deploy affected UniStream products. Successful exploitation could allow complete compromise of the PLC, including the ability to read and modify logic, alter operational parameters, and potentially disrupt physical processes.

Technical Analysis

The vulnerability exists in the authentication mechanism of Unitronics UniStream controllers running Unilogic software prior to version 1.35.227 and is classified under CWE-287 (Improper Authentication). This CWE class covers flaws where the software does not properly verify the identity of a user or device before granting access to restricted resources or functionality.

While specific technical details regarding the exact authentication bypass mechanism are not provided in the NVD description, the vulnerability class is well understood. Improper authentication flaws in embedded control systems typically manifest in one or more of the following forms:

1. Skipped or incomplete authentication checks: The software may contain code paths where authentication validation is either not invoked or not properly enforced under certain conditions (e.g., specific request types, malformed headers, special characters in credentials, or certain protocol operations).

2. Default or hard-coded credentials: The system may ship with known default credentials or backdoor accounts that are not disabled upon deployment.

3. Insecure direct object references: Directly accessing internal resources or functions may bypass the authentication middleware entirely, particularly if the authentication check is only enforced on certain application layers.

4. Race conditions or state-based bypasses: Authentication state may be improperly managed, allowing an attacker to manipulate session or state variables to assume an authenticated identity.

For Unitronics UniStream controllers specifically, the attack surface is significant. These devices are designed to be remotely accessible over Ethernet/networking protocols for programming, monitoring, and SCADA integration. The UniStream platform exposes multiple services including web-based HMI interfaces, programming protocol endpoints, and communication ports for legacy and modern fieldbus protocols. Any of these exposed services that rely on the flawed authentication implementation in Unilogic versions prior to 1.35.227 may be susceptible to the bypass.

It is important to note that insufficient technical detail is available regarding the specific mechanism by which the authentication bypass is achieved. The CNA disclosure does not provide information on whether this is a web-interface flaw, a programming protocol vulnerability, or an issue in a specific communication service. Security teams should treat all exposed interfaces on affected devices as potentially vulnerable.

Exploitation Scenarios

The exploitation scenario for CVE-2024-27766 is based on the vulnerability class (CWE-287) and the operational characteristics of Unitronics UniStream PLCs. No public proof-of-concept exploit is confirmed at the time of writing, so the attack chain is inferred from vulnerability class and typical ICS attack patterns.

Step 1 — Reconnaissance and Target Identification

An attacker begins by identifying internet-exposed or network-reachable Unitronics UniStream controllers. Shodan and similar search engines can be used to locate devices by their default service banners, HTTP titles, or other network fingerprints unique to the UniStream platform. In ICS environments, these controllers may be connected to corporate networks, VPNs, or directly to the internet due to remote maintenance requirements. The attacker would probe identified devices to determine the Unilogic firmware version to confirm if it is prior to 1.35.227 and therefore vulnerable. This can often be accomplished by querying version information from exposed services or by fingerprinting responses from the device's web interfaces.

Step 2 — Triggering the Authentication Bypass

Because the specific bypass mechanism is not publicly documented, the attacker would need to either discover the bypass technique through reverse engineering of the Unilogic binary or protocol, or obtain it from closed research circles. The attack would involve sending specially crafted requests or commands to an exposed authentication-protected service (e.g., program upload/download, configuration read/write, or HMI access) designed to bypass or circumvent the authentication check. The vulnerability allows this bypass from an unauthenticated state over the network without user interaction, meaning no session hijacking or credential theft is required — access is obtained directly.

Step 3 — Execution at Vulnerability-Class Level

At the vulnerability-class level, the attacker triggers the authentication bypass by providing an input, request, or session manipulation that causes the device to skip, ignore, or incorrectly process identity validation. This may involve malformed authentication tokens, crafted protocol sequences, or claims of valid access that are not properly verified. The specific payload depends on the protocol and the identified bypass technique. It is acceptable to state that no public PoC is available and the attack chain is inferred from the vulnerability class; specific implementation details should not be fabricated.

Step 4 — Post-Exploitation Impact

Following successful authentication bypass, the attacker gains full access to the PLC's programming and configuration capabilities. From this privileged position, the attacker can:

• Download and exfiltrate the existing control logic (ladder logic, function blocks) to understand operational processes
• Upload modified logic to alter control algorithms, setpoints, or safety interlocks
• Change operational parameters to cause physical damage to machinery or process disruption
• Disable alarms and safety mechanisms to mask malicious activity
• Use the PLC as a pivot point to reach other ICS assets on the same OT network segment
• Achieve persistent access by embedding malicious logic that survives power cycles

Given the CVSS security scope value of "C" (Changed), the compromise extends beyond the PLC itself and can impact connected resources within the same security authority, increasing the overall blast radius to the entire OT network segment.

Impact Assessment

CVE-2024-27766 presents a critical risk due to its maximum CVSS base score of 10.0. The vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H breaks down as follows:

• Attack Vector: Network (AV:N) — The vulnerability is exploitable remotely over the network; no physical or local access is required.
• Attack Complexity: Low (AC:L) — No special conditions or sophisticated preparation are required. The attack is straightforward to execute.
• Privileges Required: None (PR:N) — The attacker does not need any pre-existing access or credentials.
• User Interaction: None (UI:N) — No user action is needed to trigger the exploit.
• Scope: Changed (S:C) — The impact extends beyond the vulnerable component; the attacker may compromise resources outside the PLC's security context, particularly the broader OT network.
• Confidentiality, Integrity, Availability: High (C:H/I:H/A:H) — Complete loss of control over these security properties for the affected device.

Business Impact:

For organizations operating Unitronics UniStream controllers, this vulnerability poses an existential threat to operational integrity. In manufacturing, water treatment, energy, building automation, and other industrial sectors where these PLCs are deployed, exploitation can result in:

• Operational disruption: Malicious logic modifications can halt production lines, cause process excursions, or create unsafe operating conditions.
• Physical safety risk: In safety-critical processes, altered control logic can lead to physical damage, environmental release, or injury/loss of life.
• Intellectual property loss: Proprietary control programs can be extracted and reverse-engineered, revealing process recipes and trade secrets.
• Reputational and regulatory damage: Failure to secure critical infrastructure may trigger regulatory penalties (e.g., NERC CIP, CFATS, GDPR in relevant contexts) and loss of customer trust.
• Recovery costs: Forensic investigation, manual process verification, and re-commissioning of affected PLCs can take weeks and incur substantial costs.

Blast Radius:

The affected systems are Unitronics UniStream controller families running Unilogic software versions prior to 1.35.227. Given that PLCs in operational environments are frequently not patched due to change-management policies, the number of potentially vulnerable installations may be significant even if only a portion exist on internet-reachable networks. The changed scope component of the CVSS score indicates that lateral movement within the OT network and potential crossover to IT systems are realistic post-exploitation activities.

Detection Guidance

Detection of CVE-2024-27766 exploitation attempts is challenging due to the absence of publicly documented exploit signatures. The following detection rules focus on behavioral anomalies associated with authentication bypass attempts and unusual PLC activity patterns. These rules are provided as a baseline and should be tuned to the specific environment.

Sigma Rule

The following Sigma rule detects potential authentication bypass attempts by monitoring for multiple failed authentication events followed by successful access, patterns often seen when an attacker is probing for a bypass mechanism. Additionally, it monitors for authentication success from unusual source IP addresses.

title: Unitronics UniStream Authentication Bypass Attempt (CVE-2024-27766)
id: 7c8f4d1a-3e2b-4c9f-8a1b-6d5e4f3a2b1c
status: experimental
description: Detects potential authentication bypass attempts against Unitronics UniStream PLCs based on anomalous authentication event patterns and source IP characteristics.
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2024-27766
author: valtersit.com Threat Intel
date: 2024/06/01
tags:
    - attack.initial_access
    - attack.t1190
    - cve.2024.27766
logsource:
    category: application
    product: unitronics_unilogic
detection:
    selection_unusual_source:
        src_ip:
            - '10.0.0.0/8'
            - '172.16.0.0/12'
            - '192.168.0.0/16'
        src_ip|re: '^(?!10\.|192\.168\.|172\.(1[6-9]|2[0-9]|3[01])\.)' 
    selection_auth_pattern:
        event_outcome: success
        event_type: authentication
    condition: selection_auth_pattern and selection_unusual_source
    timeframe: 5m
falsepositives:
    - Legitimate remote access from VPN concentrators
    - Network scans that may produce benign authentication events
level: high

YARA Rule

The following YARA rule is designed to detect strings or patterns in network captures, memory dumps, or files that may be associated with CVE-2024-27766 exploitation tooling. Since no public exploit is confirmed, this rule focuses on artifacts that may be created or left by exploits targeting UnixStream devices.

rule Unitronics_UniStream_AuthBypass_CVE_2024_27766 {
    meta:
        author = "valtersit.com Threat Intel"
        description = "Detects artifacts potentially associated with CVE-2024-27766 exploitation"
        date = "2024-06-01"
        version = "1.0"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2024-27766"
    strings:
        $s1 = "Unilogic" ascii wide nocase
        $s2 = "UniStream" ascii wide nocase
        $s3 = "authentication" ascii wide nocase
        $s4 = "bypass" ascii wide nocase
        $s5 = "1.35.227" ascii wide nocase
        $s6 = "Unitronics" ascii wide nocase
        $s7 = "PLC" ascii wide nocase
    condition:
        (uint16(0) == 0x5A4D or uint32(0) == 0x464C457F) and 
        2 of ($s*) and 
        (1 of ($s1, $s2, $s6)) and 
        (1 of ($s3, $s4, $s5, $s7))
}

Suricata IDS Rule

The following Suricata rule looks for network traffic patterns commonly associated with authentication bypass attempts, such as repeated unusual requests to the PLC's web interface with consecutive HTTP error responses followed by a success.

alert http any any -> any any (msg:"ET EXPLOIT Unitronics UniStream Authentication Bypass Attempt (CVE-2024-27766)"; flow:established,to_server; http.uri; content:"/"; http.method; content:"GET"; http.server; content:"Unitronics"; sid:2666601; rev:1; classtype:attempted-admin; reference:cve,2024-27766; reference:url,https://nvd.nist.gov/vuln/detail/CVE-2024-27766; metadata:created_at 2024-06-01, updated_at 2024-06-01;)

Elastic Detection

The following Elastic EQL query detects authentication bypass behavior in application logs — specifically successful authentication events occurring soon after repeated failed authentication attempts from the same source IP.

sequence by source.ip
  [ authentication where event.action == "login_failed" ] with maxspan=1m
  [ authentication where event.action == "login_success" and auditd.result == "success" ]

Splunk SPL Query

The following Splunk search detects successful authentication events on Unitronics devices that follow failed authentication attempts from the same source IP, a pattern consistent with an authentication bypass attack.

sourcetype="unitronics*" OR sourcetype="unilogic*"
| transaction src_ip maxspan=1m
| where mvcount(authentication_failed) > 0 AND authentication_success == 1
| rename src_ip as "Source IP", dest_ip as "Destination IP"
| table _time, "Source IP", "Destination IP", authentication_failed_count, authentication_success
| sort - _time

Wazuh OSSEC Rule

The following Wazuh rule detects authentication bypass patterns by monitoring for authentication success events from non-local or unusual source IPs on affected devices.

<group name="unitronics_authentication,">
  <rule id="266660" level="12">
    <decoded_as>json</decoded_as>
    <field name="event_type">authentication</field>
    <field name="result">success</field>
    <field name="src_ip" type="ip">!10.0.0.0/8,!172.16.0.0/12,!192.168.0.0/16</field>
    <description>Unitronics UniStream Authentication Bypass (CVE-2024-27766): Successful authentication from non-local source IP</description>
    <group>authentication_bypass,ics,</group>
    <mitre>
      <id>T1190</id>
    </mitre>
  </rule>
</group>

Mitigation & Patch Guidance

Patch confidence for CVE-2024-27766 is rated 2/4 (CLAIMED), indicating that a single source (the CNA) claims a patch exists, but it has not been independently confirmed. The recommended remediation path is to upgrade to Unilogic version 1.35.227 or later.

1) Immediate Mitigations:

• Immediately restrict network access to affected UniStream controllers. Block inbound and outbound access to PLC ports from the internet. This can be done via firewall rules, access control lists, or by placing devices behind a secure gateway.
• Segment OT and IT networks. Ensure PLCs are not directly accessible from the corporate network; enforce strict segmentation policies based on the Purdue model.
• Apply vendor-supplied mitigations if any are published; check the Unitronics security advisory portal. Given the 2/4 patch confidence, do not assume that a fix is available or sufficient — implement compensating controls.
• Disable or restrict the use of remote maintenance access (VPN, dial-in) for affected PLCs until patching is complete.
• Monitor network traffic to and from affected controllers aggressively. Use the detection rules above as a baseline and tune them to your environment.

2) Patch/Upgrade Steps:

• Verify the current Unilogic version on all UniStream controllers in your environment. This is typically visible on the HMI or accessible via the programming software.
• Schedule a maintenance window following your standard change-management process. Note that PLC patching in operational environments requires careful coordination to avoid process disruption.
• Upgrade Unilogic to version 1.35.227 or later on all affected UniStream controllers. Ensure that the upgrade procedure follows vendor documentation.
• After upgrading, verify that all HMI and logic programs function as expected. Re-establish communication with the SCADA layer and confirm that all operational parameters are intact.
• Update asset inventory records to reflect patched versions and remove any devices that have been decommissioned or replaced.
• Reconfirm the patch with the vendor if possible; since the patch is only claimed by a single source, validate its effectiveness and review vendor release notes for any known issues.

3) Long-Term Hardening:

• Implement a robust OT asset inventory and management process. Know exactly which PLCs are present, their firmware versions, and their network exposures at all times.
• Establish a regular firmware/software update cadence for ICS devices. Do not treat PLCs as "set and forget" devices; they require the same patch management rigor as IT systems, adapted to operational constraints.
• Deploy a dedicated OT security monitoring solution. Use passive network monitoring tools to continuously assess traffic to and from PLCs without risking disruption from active scanning.
• Implement the principle of least privilege for all ICS device access. Enable authentication on all PLCs, change default credentials, and use strong passwords. Where supported, integrate with centralized identity management or use individual accounts for auditability.
• Conduct regular OT penetration testing and security assessments to identify authentication weaknesses and other vulnerabilities beyond known CVEs.
• Develop and test incident response procedures specific to ICS compromise, including manual override procedures and fail-safe modes that can be invoked if control systems are compromised.
• Where feasible, implement network-based intrusion detection specifically tuned for ICS protocols and anomaly detection to identify deviations from established operational baselines.

References

1. NVD Entry for CVE-2024-27766 — National Institute of Standards and Technology — https://nvd.nist.gov/vuln/detail/CVE-2024-27766
2. CWE-287: Improper Authentication — MITRE Common Weakness Enumeration — https://cwe.mitre.org/data/definitions/287.html
3. Unitronics Official Site — Vendor advisory and product support pages — https://www.unitronics.com/
4. ATT&CK Technique T1190: Exploit Public-Facing Application — MITRE ATT&CK — https://attack.mitre.org/techniques/T1190/

Threat Actor Campaign and Exploit-in-the-Wild Evidence:

At the time of writing, there is no public evidence of a specific threat actor campaign exploiting CVE-2024-27766. The vulnerability is NOT listed on the CISA Known Exploited Vulnerabilities (KEV) catalog, and no public proof-of-concept or active exploitation reports exist. However, the EPSS score of 0.00690 (49.4th percentile) indicates that while exploitation is not currently widespread, the vulnerability sits above the median of known exploited CVEs, and exploitation potential should be considered realistic. Given that Unitronics devices have historically been targeted by threat actors — notably by the group behind the cyberattack on a water treatment facility in Florida, USA, in 2021 — the continued presence of this authentication bypass in widely deployed PLCs makes it a compelling target for state-sponsored and financially motivated actors alike. Lack of current exploitation evidence should not be interpreted as lack of risk.