CVE-2026-76940

Executive Summary

CVE-2026-76940 affects Ebyte network devices that rely on password-based authentication. The vulnerability stems from a lack of rate limiting and account lockout mechanisms on the authentication interface, enabling remote attackers to perform automated brute-force attacks without restriction. Successful exploitation could grant unauthorized access to device management interfaces, potentially exposing sensitive configuration data or allowing further network compromise. As of this writing, no vendor patch is available, and the vulnerability remains unpatched.

Technical Analysis

CVE-2026-76940 is a CWE-307 (Improper Restriction of Excessive Authentication Attempts) vulnerability found in Ebyte devices. The NVD description indicates that the affected device fails to implement rate limiting or account lockout mechanisms for repeated authentication attempts. This omission removes the primary defensive barrier against brute-force and credential-stuffing attacks.

The attack surface is the device's authentication endpoint, which processes password-based login requests. In a properly implemented authentication system, repeated failed attempts would trigger either a temporary or permanent lockout, or the system would progressively slow down responses to thwart automated guessing. In this vulnerable configuration, neither control exists, meaning an attacker can submit an unlimited number of authentication requests within any given time window.

The vulnerability is accessible over the network (CVSS AV:N) with low attack complexity (AC:L). No privileges (PR:N) or user interaction (UI:N) are required before exploitation. The scope is unchanged (S:U), meaning the compromised component is confined to the device itself. The confidentiality impact is rated high (C:H), suggesting that successful authentication could expose sensitive information stored on or managed by the device.

From a code-level perspective, the flaw likely resides in the authentication handler where the server compares submitted credentials against stored hashes. The absence of middleware or logic that counts consecutive failures and enforces a delay or disables the account constitutes the vulnerability. Specific implementation details (function names, endpoints) are not available in the CVE description, so the analysis is restricted to the vulnerability class level.

Exploitation Scenarios

No public proof-of-concept (PoC) is available for this CVE, and no exploit code exists in public repositories. The attack chain below is inferred from the vulnerability class (CWE-307) and the CVSS vector.

Step 1 — Reconnaissance / Target Identification: An attacker first identifies Ebyte devices exposed to the network or internet. This may be accomplished through network scanning tools that detect Ebyte-specific service banners, default ports, or web management interfaces. Shodan-style queries using terms like "Ebyte" could assist in finding internet-facing deployments.

Step 2 — Triggering the Flaw: The attacker directs repeated authentication requests to the device's login interface. Because no rate limiting or account lockout exists, each failed attempt returns a response that allows another attempt. Unlike hardened systems that would block the source IP or lock the account after N failures, this device permits continuous retries.

Step 3 — Payload / Execution Method: At the vulnerability-class level, the attacker uses automated tools such as Hydra, Medusa, or custom Python scripts to iterate through username/password combinations. The payload is essentially the authentication request itself; the flaw is that the server does not reject or throttle these requests. Default credentials, weak passwords, or credentials leaked from other breaches are viable candidates.

Step 4 — Post-Exploitation Impact: Upon successful authentication, the attacker gains access to the device's management interface. Given the high confidentiality impact rating in the CVSS vector, the attacker may be able to read configuration data, network credentials, or other sensitive information. Depending on the device type, the attacker could potentially modify settings, intercept traffic, or pivot into the internal network.

Attacker Profile: This vulnerability is particularly attractive to botnet operators seeking to expand their inventory of compromised devices, as well as to attackers conducting opportunistic scanning of internet-facing hardware. The lack of authentication controls makes the device a low-hanging fruit for automated exploitation campaigns.

Impact Assessment

The business impact of CVE-2026-76940 depends heavily on the deployment context of the affected Ebyte device. Ebyte manufactures wireless communication modules and IoT devices commonly used in industrial, agricultural, and remote monitoring environments. A compromised device could expose:

• Configuration Data: Network topology, IP addressing schemes, and connection parameters that aid further attacks.
• Credential Material: If the device stores or forwards credentials for upstream systems.
• Operational Telemetry: Sensitive industrial or environmental data that the device collects or relays.

The CVSS subscores break down as follows: Attack Vector (AV:N) confirms the vulnerability is remotely exploitable. Attack Complexity (AC:L) means no special conditions are required. Privileges Required (PR:N) indicates unauthenticated exploitation. User Interaction (UI:N) confirms no victim interaction is necessary. The high confidentiality impact (C:H) reflects the potential exposure of sensitive data.

The availability impact is rated none (I:N, A:N), suggesting the attacker cannot directly disrupt device operation. However, an attacker who gains authenticated access may be able to alter device behavior in ways that indirectly affect availability.

Blast Radius: If these devices sit at network boundaries or in demilitarized zones, successful exploitation could provide a foothold for lateral movement into internal networks. If deployed in isolated IoT segments, the blast radius may be limited to the device and its immediate data flows. Given that the affected version range is unspecified, the entire Ebyte product line may be susceptible, making the potential exposure broad across verticals.

Detection Guidance

Sigma Rule

title: Ebyte Device Brute Force Attempt
id: 4c9b8f2e-7d43-4e05-9b1e-6a3f2b8c9d10
status: experimental
description: Detects repeated failed authentication attempts against Ebyte device management interfaces
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2026-76940
author: Valtersit Threat Intelligence
date: 2026/04/15
logsource:
    category: application
    product: ebyte
detection:
    selection:
        event.category: authentication
        event.outcome: failure
    condition: selection | count() by src.ip > 10 within 5m
level: high
falsepositives:
    - Legitimate user mistyping password
    - Misconfigured client retry logic
tags:
    - attack.t1110
    - cve.2026-76940

YARA Rule

rule Ebyte_Brute_Force_Tooling
{
    meta:
        author = "Valtersit Threat Intelligence"
        description = "Detects common brute-force patterns targeting Ebyte devices"
        date = "2026-04-15"
        cve = "CVE-2026-76940"
        severity = "high"
    strings:
        $s1 = "Ebyte" ascii wide nocase
        $s2 = "login" ascii wide nocase
        $s3 = "password" ascii wide nocase
        $s4 = "auth_failed" ascii wide nocase
        $s5 = "401 Unauthorized" ascii wide nocase
        $s6 = "Invalid credentials" ascii wide nocase
    condition:
        uint16(0) == 0x5A4D and 2 of ($s*) 
        or filesize < 500KB and 2 of ($s*)
}

Suricata IDS Rule

alert http any any -> $HOME_NET any (msg:"ET SCAN Ebyte Device Brute Force Attempt"; flow:to_server,established; content:"POST"; http_method; content:"login"; http_uri; content:"password"; http_client_body; threshold:type threshold, track by_src, count 10, seconds 300; classtype:attempted-admin; sid:20267694001; rev:1; metadata:created_at 2026_04_15, updated_at 2026_04_15, cve CVE-2026-76940, tag brute-force;)

Note: The rule uses generic HTTP parameters ("login", "password") since the exact Ebyte endpoints are not disclosed in the CVE data. Adjust the URI and body fields to match actual traffic once endpoint information becomes available.

Elastic Detection

sequence by source.ip with maxspan=5m
  [authentication where event.outcome == "failure" and 
   process.name : "*ebyte*" or winlog.event_data.TargetUserName : "*admin*"]
  [authentication where event.outcome == "failure"]
  [authentication where event.outcome == "failure"]
  [authentication where event.outcome == "failure"]
  [authentication where event.outcome == "success"]

Note: This EQL rule detects a pattern of multiple failed authentications followed by a successful one, which is indicative of successful brute-force exploitation. Adjust field names based on your actual data source (Windows EventLog, auditbeat, etc.).

Splunk SPL Query

index=* sourcetype=auth_logs 
| where like(_raw, "%ebyte%") OR like(_raw, "%Ebyte%") 
| stats count as failed_attempts, values(user) as attempted_users, 
        last(_time) as last_attempt by src_ip 
| eval threshold_time = now() - 300 
| where _time > threshold_time 
| where failed_attempts > 10 
| table src_ip, failed_attempts, attempted_users, last_attempt

Alternatively, a more generic detection for any authentication failure storm:

index=auth sourcetype=*auth* "authentication failed" OR "login failed" OR "invalid password"
| bin _time span=5m
| stats count as failures by src_ip, _time
| where failures > 10
| table _time, src_ip, failures

Wazuh OSSEC Rule

<group name="ebyte_bruteforce,">
    <rule id="100001" level="10" frequency="10" timeframe="300">
        <match>authentication failed|login failed|invalid password|401 Unauthorized</match>
        <description>Multiple failed authentication attempts - possible Ebyte brute force</description>
        <group>authentication_failures,brute_force,</group>
        <mitre>
            <id>T1110</id>
        </mitre>
    </rule>
</group>

Mitigation & Patch Guidance

Patch Confidence: 0/4 — UNPATCHED. No vendor advisory, patch, or fixed version has been identified from any tracked source. The vendor has not released a security update for CVE-2026-76940, and the affected version range remains unspecified.

1. Immediate Mitigations (until vendor patch is available)

• Restrict Network Access: Place Ebyte devices behind a firewall or VPN. Do not expose the management interface directly to the internet. Use access control lists (ACLs) to permit only known administrative IP addresses.
• Implement External Rate Limiting: Deploy a reverse proxy or Web Application Firewall (WAF) in front of the device that enforces rate limiting on authentication endpoints. Configure thresholds (e.g., 5 attempts per 60 seconds per source IP) and temporary blocks.
• Enforce Strong Passwords: Replace any default credentials with long, unique, complex passwords. Disable any default accounts if possible.
• Segment the Network: Isolate Ebyte devices into a separate VLAN or network segment with minimal ingress/egress rules to limit lateral movement if compromised.
• Monitor Authentication Logs: Enable and regularly review authentication logs. Use the detection rules above to alert on anomalous authentication patterns.

2. Patch / Upgrade Steps

• Monitor Vendor Channels: Regularly check Ebyte's official website, security advisories, and firmware release notes for a fix. As of this report, no fix exists.
• Firmware Updates: When available, apply firmware updates immediately. Validate the update's integrity (checksum/hash) before deployment.
• Contact Vendor: Open a support ticket with Ebyte to request a security patch and disclose your affected deployment details.

3. Long-Term Hardening

• Disable Remote Management: If the device supports local-only configuration (serial console or USB), disable remote web/SSH access entirely.
• Use Certificate-Based Authentication: If the device supports it, replace password authentication with client certificates or public-key infrastructure (PKI) to eliminate the brute-force surface.
• Network Monitoring: Deploy continuous network monitoring to detect scanning or brute-force patterns targeting any "Ebyte" branded device.
• Inventory Management: Maintain a complete asset inventory of all Ebyte devices, including firmware versions, network locations, and responsible owners. This enables rapid response when a patch becomes available.
• Consider Replacement: For critical deployments where patching is unlikely (abandoned devices or vendor no longer supports the product line), evaluate replacing the device with a vendor that has a demonstrated security response process.

References

1. NVD Entry: https://nvd.nist.gov/vuln/detail/CVE-2026-76940 (NVD description, CVSS vector, CWE classification)
2. CWE-307 Reference: https://cwe.mitre.org/data/definitions/307.html (Improper Restriction of Excessive Authentication Attempts — technical background on the vulnerability class)
3. MITRE ATT&CK T1110: https://attack.mitre.org/techniques/T1110/ (Brute Force — associated adversary technique)
4. Ebyte Official Site: https://www.ebyte.com (Vendor site for advisories and firmware updates; no security advisory issued as of this report)
5. CISA KEV Catalog: https://www.cisa.gov/known-exploited-vulnerabilities-catalog (Not listed; no evidence of exploitation in the wild, but also no patch available)

Threat Actor Campaigns / Exploitation in the Wild: No known threat actor campaigns have been publicly attributed to this CVE, and there is no evidence of active exploitation. However, the vulnerability's characteristics — network-exploitable, unauthenticated, and unpatched — make it a strong candidate for inclusion in IoT botnet operations. Security teams should treat this as a significant risk and monitor closely for emerging exploitation activity.