CVE-2024-36650: Totolink A3100r Buffer Overflow Flaw

CVE-2024-36650 Overview

CVE-2024-36650 is a buffer overflow vulnerability in the TOTOLINK AC1200 Wireless Dual Band Gigabit Router, affecting firmware version A3100R V4.1.2cu.5247_B20211129. The flaw resides in the setNoticeCfg CGI function within /lib/cste_modules/system.so. The function fails to validate the length of the user-supplied NoticeUrl parameter before processing it. Remote attackers can send crafted HTTP or MQTT requests containing oversized NoticeUrl values to trigger memory corruption and crash the device. The vulnerability is tracked under [CWE-120] (Buffer Copy without Checking Size of Input).

Critical Impact

Unauthenticated network attackers can trigger a denial-of-service condition on affected routers by submitting oversized NoticeUrl strings to the setNoticeCfg CGI endpoint.

Affected Products

• TOTOLINK A3100R Router (hardware)
• TOTOLINK A3100R Firmware version 4.1.2cu.5247_B20211129
• TOTOLINK AC1200 Wireless Dual Band Gigabit Router series

Discovery Timeline

• 2024-06-11 - CVE-2024-36650 published to NVD
• 2025-06-04 - Last updated in NVD database

Technical Details for CVE-2024-36650

Vulnerability Analysis

The vulnerability resides in the setNoticeCfg handler exported by the shared object /lib/cste_modules/system.so. This CGI endpoint processes configuration requests that include a NoticeUrl parameter. The handler copies the attacker-controlled string into a fixed-size stack buffer without enforcing a length check. When the input exceeds the destination buffer size, adjacent stack memory is overwritten, corrupting saved registers and the return address.

The resulting memory corruption crashes the HTTP daemon and renders the router unresponsive to legitimate management traffic. Because the vulnerable endpoint accepts both HTTP and MQTT requests, attackers have multiple delivery channels for the malicious payload. Recovery requires a device reboot.

Root Cause

The root cause is the absence of bounds checking on the NoticeUrl parameter before it is copied into a stack buffer inside setNoticeCfg. The function relies on unsafe string operations that copy until a null terminator is encountered. No upper bound is applied to the input length, which violates the secure coding requirement to validate length before copying untrusted input.

Attack Vector

Exploitation requires network access to the router's management interface. No authentication or user interaction is needed. An attacker constructs an HTTP POST or MQTT message that invokes setNoticeCfg with an overlong NoticeUrl value. Upon receipt, the CGI process parses the request, copies the oversized string, and crashes. Repeated requests maintain the denial-of-service condition. Technical details and proof-of-concept information are available in the GitHub Gist PoC Code.

No verified exploitation code is reproduced here. Refer to the linked PoC for technical reproduction details.

Detection Methods for CVE-2024-36650

Indicators of Compromise

• Unexpected reboots or service restarts of the TOTOLINK A3100R router management daemon
• HTTP or MQTT requests targeting the setNoticeCfg endpoint with abnormally long NoticeUrl parameter values
• Loss of administrative web interface availability without operator action
• Crash logs referencing system.so or the CGI handler process

Detection Strategies

• Inspect inbound HTTP traffic to router management interfaces for POST requests containing NoticeUrl fields exceeding typical URL lengths
• Monitor MQTT broker traffic for messages invoking setNoticeCfg with oversized parameters
• Deploy network intrusion detection rules that flag CGI parameter values exceeding 256 bytes on embedded device management endpoints
• Correlate router availability monitoring with traffic captures to identify denial-of-service patterns

Monitoring Recommendations

• Enable uptime and reachability monitoring for all TOTOLINK A3100R devices to detect repeated reboots
• Log all administrative access attempts to router CGI endpoints and forward to a central SIEM
• Alert on traffic volume spikes targeting the management interface from external sources
• Track firmware versions across the router fleet to prioritize remediation of affected devices

How to Mitigate CVE-2024-36650

Immediate Actions Required

• Restrict access to the router management interface to trusted internal networks only
• Disable WAN-side administrative access and MQTT services if not required
• Place affected TOTOLINK A3100R devices behind a network firewall that blocks untrusted inbound connections
• Inventory all TOTOLINK A3100R routers running firmware 4.1.2cu.5247_B20211129 and prioritize replacement or isolation

Patch Information

No vendor advisory or patched firmware release has been published in the available references. Operators should monitor the TOTOLINK official support site for updated firmware. Until a fix is available, network-level controls remain the primary defense.

Workarounds

• Block external access to the router's HTTP management interface using upstream firewall rules
• Disable the MQTT service on the router if the deployment does not require it
• Segment vulnerable routers onto isolated VLANs that limit exposure to untrusted clients
• Replace affected devices with hardware that receives active security maintenance if no patch becomes available

# Example upstream firewall rule to restrict router management access
# Allow management only from trusted admin subnet 10.0.0.0/24
iptables -A FORWARD -p tcp -d <router_ip> --dport 80 -s 10.0.0.0/24 -j ACCEPT
iptables -A FORWARD -p tcp -d <router_ip> --dport 80 -j DROP
iptables -A FORWARD -p tcp -d <router_ip> --dport 1883 -j DROP