CVE-2024-28751: Authentication Bypass Vulnerability

CVE-2024-28751 Overview

CVE-2024-28751 describes a hardcoded credentials weakness disclosed through VDE Security Advisory VDE-2024-012. A high-privileged remote attacker can enable a telnet service that accepts hardcoded credentials embedded in the affected product. Once telnet is enabled, any actor who knows the embedded credentials can authenticate over the network. The flaw is categorized under [CWE-798] (Use of Hard-coded Credentials) and carries a network attack vector with changed scope, affecting confidentiality, integrity, and availability.

Critical Impact

An authenticated attacker with high privileges can activate a telnet interface that grants access via fixed credentials, exposing the device to full compromise from anyone who knows or recovers those credentials.

Affected Products

• Product details published through the VDE CERT advisory VDE-2024-012
• Specific vendor and product identifiers were not populated in the NVD record at time of writing
• Refer to the VDE Security Advisory VDE-2024-012 for the authoritative list of affected models and firmware versions

Discovery Timeline

• 2024-07-09 - CVE-2024-28751 published to NVD
• 2026-04-15 - Last updated in NVD database

Technical Details for CVE-2024-28751

Vulnerability Analysis

The vulnerability allows a remote actor with high privileges to switch on a telnet service that has been shipped with hardcoded credentials. Telnet transmits credentials and session data in cleartext, so any subsequent authentication using the embedded credentials traverses the network without protection. The condition combines two distinct weaknesses: an administrative function that activates a legacy management service, and a backend account whose credentials cannot be changed by operators.

Because the credentials are static across deployments, recovery of the secrets from a single device or from firmware extraction is sufficient to authenticate against every other affected device on which telnet has been enabled. Successful exploitation grants the attacker the privileges associated with the embedded account, which typically exceed those of a standard operator.

Root Cause

The root cause is the inclusion of fixed authentication material inside the device firmware, mapped to [CWE-798]. The affected service trusts credentials that are stored in the image rather than provisioned per device, and there is no mechanism documented for operators to rotate or disable the credentials independently of disabling the service.

Attack Vector

Exploitation requires network reachability to the management interface and an account with high privileges to first enable telnet. After activation, an attacker with knowledge of the embedded credentials authenticates over TCP without requiring user interaction. The changed scope component reflects that compromise of the telnet account can affect resources beyond the originally authorized component.

No public proof-of-concept code is referenced in the advisory, and no verified exploitation in the wild has been reported.

Detection Methods for CVE-2024-28751

Indicators of Compromise

• Unexpected inbound TCP connections to port 23 on affected devices
• Configuration changes that enable the telnet service outside approved maintenance windows
• Authentication events on the device using accounts that are not part of the operator identity store
• New administrative sessions originating from unfamiliar source IP addresses

Detection Strategies

• Audit device configuration exports for telnet-enable directives and alert on any deviation from a known-good baseline
• Inspect network telemetry for cleartext telnet traffic on operational technology and management VLANs
• Correlate privileged configuration changes with the identity of the operator who performed them to detect account abuse

Monitoring Recommendations

• Forward device syslog and configuration audit events to a centralized log platform for retention and search
• Create alerts that fire when telnet is enabled, when a session is established, or when authentication succeeds against the embedded account
• Continuously scan the management network for listening telnet services and flag any new exposures

How to Mitigate CVE-2024-28751

Immediate Actions Required

• Apply the firmware update referenced in VDE Security Advisory VDE-2024-012 once available for your hardware revision
• Verify that telnet is disabled on every affected device and remove any saved configurations that enable it
• Restrict the management interface to a dedicated administration network protected by firewall rules and jump hosts
• Review and reduce the number of accounts that hold the high-privilege role required to enable telnet

Patch Information

Refer to VDE Security Advisory VDE-2024-012 for vendor-supplied firmware versions that remediate the hardcoded credentials issue. Validate firmware integrity before deployment and follow the vendor change-control guidance for production devices.

Workarounds

• Block TCP port 23 at perimeter and segmentation firewalls to prevent reachability of telnet from untrusted networks
• Use access control lists on the device itself to restrict management protocols to authorized administrative hosts
• Require administrators to authenticate through an out-of-band management network with multi-factor authentication on the upstream jump host
• Monitor for and alert on any configuration command that toggles the telnet service state

# Example perimeter rule to block telnet to device management subnet
iptables -A FORWARD -p tcp --dport 23 -d 10.10.20.0/24 -j DROP
iptables -A FORWARD -p tcp --sport 23 -s 10.10.20.0/24 -j DROP