CVE-2024-1786: D-Link DIR-600M Buffer Overflow Vulnerability

CVE-2024-1786 Overview

CVE-2024-1786 is a buffer overflow vulnerability [CWE-120] in the D-Link DIR-600M C1 router running firmware version 3.08. The flaw resides in the Telnet Service component, where improper handling of the username argument allows an unauthenticated remote attacker to trigger memory corruption. Successful exploitation results in denial of service against the affected device. The vendor confirmed the product is end-of-life and will not receive a patch. A public proof-of-concept is available, increasing the risk for any device still deployed on production networks.

Critical Impact
Unauthenticated remote attackers can crash the Telnet service on end-of-life D-Link DIR-600M C1 routers running firmware 3.08, with no vendor fix planned.

Affected Products

D-Link DIR-600M C1 hardware revision
D-Link DIR-600M firmware version 3.08
All deployments exposing the Telnet service

Discovery Timeline

2024-02-23 - CVE-2024-1786 published to the National Vulnerability Database (NVD)
2024-12-17 - Last updated in NVD database

Technical Details for CVE-2024-1786

Vulnerability Analysis

The vulnerability stems from a classic buffer overflow [CWE-120] in the Telnet authentication handler of the DIR-600M C1. When a client connects to the Telnet service and supplies an overly long username value, the device copies the input into a fixed-size stack buffer without bounds checking. This corrupts adjacent memory and triggers a service crash or reboot.

The attack does not require authentication or user interaction. Any host with network reachability to the router's Telnet port can deliver the malicious payload. Because the vendor declared the device end-of-life, no firmware update will be released to address the flaw.

The practical impact is loss of availability for the router. Repeated exploitation can keep the device in a continuous crash loop, disrupting all routed traffic for downstream clients. While the public proof-of-concept demonstrates a denial-of-service outcome, buffer overflows of this class can sometimes be extended toward code execution on embedded MIPS targets if attacker-controlled data overwrites the return address.

Root Cause

The root cause is the absence of length validation on the username field supplied to the Telnet daemon. The handler likely uses an unsafe string copy routine such as strcpy or sprintf into a fixed-size stack buffer, allowing the input to overwrite saved registers and the return address.

Attack Vector

The attack vector is network-based and requires no privileges. An attacker initiates a Telnet session to TCP port 23 on the router and submits a long username string. The DIR-600M C1 processes the input, overflows the buffer, and crashes the Telnet service or the entire device. A public proof-of-concept script is hosted as a GitHub Gist PoC Script. Additional technical context is published in VulDB #254576.

Detection Methods for CVE-2024-1786

Indicators of Compromise

Unexpected reboots or service restarts on DIR-600M C1 devices coinciding with inbound Telnet connections
Inbound TCP traffic to port 23 on internal D-Link router management interfaces
Telnet authentication attempts containing abnormally long username strings
Loss of routing or DHCP services from the affected device followed by recovery cycles

Detection Strategies

Inspect network flow logs for connections destined to TCP port 23 on D-Link infrastructure
Deploy intrusion detection signatures that flag Telnet USER commands exceeding typical username length thresholds
Correlate router uptime resets with preceding inbound management-plane traffic
Identify D-Link DIR-600M devices through passive fingerprinting of HTTP and Telnet banners

Monitoring Recommendations

Enable syslog forwarding from network devices to a centralized log repository for crash and reboot events
Alert on any Telnet traffic crossing segmentation boundaries into management networks
Track asset inventory for end-of-life networking hardware that remains in production
Monitor for scanning activity targeting port 23 across internal subnets

How to Mitigate CVE-2024-1786

Immediate Actions Required

Disable the Telnet service on all DIR-600M C1 devices through the administrative interface
Restrict management-plane access to the router using ACLs that block external sources from reaching port 23
Replace the DIR-600M C1 with a vendor-supported router model, as D-Link has confirmed end-of-life status
Place legacy devices behind a firewall that blocks inbound Telnet until replacement is complete

Patch Information

No patch is available. D-Link confirmed that the DIR-600M C1 is end-of-life and instructed customers to retire and replace the product. Organizations operating this hardware should treat decommissioning as the primary remediation path.

Workarounds

Disable Telnet and use SSH where supported, or migrate to a router that offers encrypted management
Apply network segmentation so the router management interface is unreachable from user and guest VLANs
Block TCP port 23 at the perimeter firewall to prevent external exploitation attempts
Document the device as end-of-life within the asset inventory and schedule prompt replacement

bash

# Example firewall rule to block inbound Telnet to the affected device
iptables -A INPUT -p tcp --dport 23 -d <router-management-ip> -j DROP
iptables -A FORWARD -p tcp --dport 23 -d <router-management-ip> -j DROP