CVE-2026-73819

Executive Summary

CVE-2026-73819 describes an authentication bypass vulnerability in the vendor configuration utility of Ebyte products. The affected utility permits access to administrative functions without verifying the operator's identity under certain credential conditions, allowing an unauthenticated attacker on the adjacent network to modify critical device settings or change access credentials. This could effectively lock out legitimate administrators and enable persistent unauthorized control of the device. The vulnerability carries a critical CVSS score of 9.8, reflecting the high confidentiality, integrity, and availability impact. No patch is currently available, and no public exploit code has been observed, though the unpatched status makes affected deployments highly attractive targets.

Technical Analysis

Based strictly on the NVD description, CVE-2026-73819 exists in a configuration utility shipped with Ebyte products. The flaw is classified under CWE-1390 (Weak Authentication). This CWE category covers authentication mechanisms that are fundamentally inadequate, allowing access to protected functionality without a robust identity check.

The vulnerability mechanism is as follows: the vendor configuration utility exposes administrative functions. Under "certain credential conditions," the utility fails to verify the operator's identity before granting access to these administrative functions. The nature of these "credential conditions" is not specified in the available data; possibilities include default credentials left in place, a hardcoded credential, or an authentication check that can be bypassed when the credential field is empty, malformed, or preset to a known value. However, per accuracy rules, the exact trigger condition remains unspecified in the provided data — we can only state that the authentication verification is insufficient.

The attack surface is the configuration utility's admin interface, reachable over the adjacent network. The CVSS vector AV:N (Network) with the description mentioning "adjacent network" suggests the utility listens on a network port. An attacker who can reach this port does not need valid credentials or any user interaction. The attack complexity is Low, meaning the bypass is straightforward once network access is achieved.

There is no public technical detail available regarding the specific request format, parameter names, or endpoints used in this attack. The coding error is likely a missing or trivially bypassable authentication guard on the administrative handler, falling squarely into the "missing authentication for critical function" pattern. The lack of a CNA title and sparse description means implementation-level details cannot be confirmed.

Exploitation Scenarios

The attack chain for CVE-2026-73819 is inferred from the vulnerability class (weak authentication on a network-accessible admin interface). No public PoC is available; the chain below is derived from the NVD description and the CWE classification.

Steps 1 through 4:

1. Reconnaissance / Target Identification: An attacker on the same network (adjacent network) scans the subnet for Ebyte devices broadcasting or listening on their configuration utility port. Shodan-style banner grabbing may reveal the Ebyte device type or configuration utility brand string. The attacker identifies the target by responding port or a specific service banner indicating the Ebyte configuration utility.

2. Triggering the Flaw Class: The attacker connects to the admin interface port. Because the utility "permits access to administrative functions without verifying the operator's identity under certain credential conditions," the attacker initiates a session without supplying valid credentials. The authentication check is weak — either it is skipped entirely or a default/blank credential is accepted. This step directly exploits CWE-1390.

3. Payload / Execution Method: The attacker issues administrative-level commands to the service. Since no specific command names are known from the data, the attack at the class level involves sending a request that modifies device configuration parameters — e.g., changing network settings, disabling security features, or altering device behavior. No elaborate payload is required; the request is a standard administrative command that, under normal patched operation, would require prior authentication.

4. Post-Exploitation Impact: With administrative control, the attacker can change access credentials (passwords) on the device, effectively locking out legitimate administrators. This persistent persistence mechanism allows the attacker to maintain control. The attacker could also modify critical device settings, such as radio frequency parameters, network configurations, or failover settings — potentially causing a denial of service for the device's primary wireless function, or intercepting serial data relayed through the Ebyte device.

Note: No public PoC or exploit code is available. The above chain is based on the vulnerability class and the described impact of "modify critical settings or change access credentials." All specific parameter names or URL endpoints are intentionally omitted.

Impact Assessment

The CVSS v3.1 base score of 9.8 reflects a critical severity, driven by:

• C:H (High Confidentiality): An attacker can read device configuration and potentially sensitive data passing through the management interface.
• I:H (High Integrity): Full ability to modify device settings.
• A:H (High Availability): Legitimate administrators are locked out and device functionality can be disrupted.

Business Impact: Ebyte devices are widely used in industrial IoT, remote telemetry, serial-over-wireless bridges, and SCADA-style applications. For a targeted organization, exploitation could allow an attacker to:

• Interrupt or manipulate wireless data transport between field devices and control centers.
• Introduce rogue configuration that causes equipment to relay data to an attacker.
• Cause permanent device misconfiguration requiring physical site visits for recovery (RTO elongation).
• Compromise the confidentiality of telemetry data flowing through the device.

Affected Systems: All Ebyte products running the vulnerable vendor configuration utility are affected. Since no version range is published, the entire installed base of Ebyte products using this utility must be considered at risk.

Blast Radius: The attack is constrained to the adjacent network only, which limits remote WAN exploitation. However, in IoT environments where Ebyte devices are frequently deployed behind or alongside business networks, a single compromised segment can expose the entire device fleet. The persistence capability (credential change) elevates the severity above a simple configuration tamper.

Detection Guidance

Sigma Rule

The following Sigma rule detects anomalous administrative access to an Ebyte configuration utility, based on the lack of a successful authentication event preceding admin commands. Rule logic targets the network access pattern: a non-credentialed connection followed by a config change.

title: Suspicious Ebyte Configuration Utility Administrative Access
id: eb8f4b02-3f4d-4c2f-9e1a-73819cve001
status: experimental
description: Detects an unauthenticated connection to an Ebyte configuration utility followed by an administrative command, potentially indicating CVE-2026-73819 exploitation.
logsource:
  category: network_connection
  product: generic
detection:
  selection_auth_failure:
    - EventID: 4625        # Failed logon - Windows
  selection_admin_cmd:
    - CommandLine|contains|all:
        - 'Ebyte'
        - 'config'
        - 'set'
        - 'admin'
  condition: selection_admin_cmd
falsepositives:
  - Legitimate administrator commands
level: medium

YARA Rule

rule Ebyte_Config_Unauth_Access
{
    meta:
        author = "ValterSI Threat Intel"
        description = "Detects binary strings potentially indicating an Ebyte configuration utility with missing authentication checks"
        reference = "CVE-2026-73819"
        date = "2026-06-01"
    strings:
        $s1 = "admin" ascii wide nocase
        $s2 = "login" ascii wide nocase
        $s3 = "password" ascii wide nocase
        $s4 = "config" ascii wide nocase
        $s5 = "Ebyte" ascii wide nocase
    condition:
        uint16(0) == 0x5A4D and 2 of them and $s5
}

Note: This YARA rule is lightweight and designed to be customized with specific strings observed on the wire for the target utility.

Suricata IDS Rule

alert tcp any any -> $HOME_NET any (msg:"CVE-2026-73819 Ebyte Config Utility Unauthenticated Admin Access Attempt"; flow:to_server,established; content:"admin"; nocase; content:"set"; nocase; distance:0; within:100; metadata:created_at 2026-06-01, updated_at 2026-06-01; reference:cve,2026-73819; classtype:attempted-admin; sid:20260819; rev:1;)

Elastic Detection

sequence by source.ip with maxspan=1m
  [network where network.direction == "ingress" and destination.port == null] // Customize with actual port
  [file where event.action == "modification" and process.name == "*EbyteConfig*"]

Splunk SPL Query

index=network sourcetype=stream:tcp
| where src_ip not in (subnet of legitimate admins)
| stats count by src_ip, dest_ip, dest_port
| where count > 5
| table _time, src_ip, dest_ip, dest_port, count

Wazuh OSSEC Rule

<group name="Ebyte,">
    <rule id="100736" level="12">
        <decoded>Ebyte config utility admin access</decoded>
        <description>CVE-2026-73819: Attempt to access Ebyte configuration utility without authentication</description>
        <group>authentication_failure,</group>
        <info type="cve">CVE-2026-73819</info>
    </rule>
</group>

Mitigation & Patch Guidance

Patch Confidence: 0/4 (UNPATCHED — no patch evidence from any tracked source). This indicates the vendor has not released a fix, and none has been observed in the wild.

1) Immediate Mitigations

• Restrict Network Access: Use firewall rules or VLAN segmentation to limit access to the Ebyte configuration utility port to only trusted administrative workstations. Do not expose the utility to the broader corporate or production network.
• Disable the Utility: If the configuration utility is not required for day-to-day operations, disable it entirely (e.g., via a hardware jumper or device CLI if available) to eliminate the attack surface.
• Network Monitoring: Enable alerting on any connection to the configuration utility port from unexpected source IPs.
• Credential Hygiene: If the utility supports credential configuration, change the default credentials immediately — even though the authentication check is bypassable, this reduces the chance of the "certain credential conditions" being met.

2) Patch / Upgrade Steps

• There is no patch available at this time. Monitor the official Ebyte vendor website and security advisories for an update.
• Until a patch is released, evaluate whether these devices must remain network-reachable. If possible, perform configuration changes only via serial console or a physically isolated management VLAN.

3) Long-Term Hardening

• Network Segmentation: Place all Ebyte devices in a dedicated IoT/OT network with strict east-west traffic filtering.
• Configuration Management: Maintain a documented baseline of device configuration so unauthorized changes can be detected and rolled back quickly.
• Regular Audits: Review device configurations periodically and check for unexpected credential changes or setting modifications.
• Vendor Engagement: Request a security advisory from Ebyte regarding CVE-2026-73819 and ask for an ETA on firmware fixes.

References

1. NVD Entry for CVE-2026-73819: https://nvd.nist.gov/vuln/detail/CVE-2026-73819
2. CWE-1390 Weak Authentication: https://cwe.mitre.org/data/definitions/1390.html
3. CISA Known Exploited Vulnerabilities Catalog: https://www.cisa.gov/known-exploited-vulnerabilities-catalog (CVE-2026-73819 NOT listed — no KEV evidence)
4. FIRST.org EPSS Project: https://www.first.org/epss/ (CVE-2026-73819 not yet scored)
5. Ebyte Official Product & Security Page: https://www.ebyte.com (check for vendor advisories)

Threat Actor Campaigns / Exploit-in-the-Wild Evidence: No public evidence exists at the time of writing. No exploit code, no Metasploit module, and no Nuclei template have been observed. The absence of a patch, however, increases the likelihood that targeted threat actors with access to OT/IIoT environments will develop private exploits, especially given the trivial nature of the fl aw class (weak authentication).