CVE-2023-31729 – CVE-2023-31729 is a command injection vulnerabi... (How to Fix)

Q: What is the severity of CVE-2023-31729?

CVE-2023-31729 has a CVSS score of 9.8 (CRITICAL). CVE-2023-31729 is a command injection vulnerability in TOTOLINK A3300R routers that allows attackers to execute arbitrary commands on the device via the /cgi-bin/cstecgi.cgi endpoint. This affects users running vulnerable firmware versions, potentially giving attackers full control over the router. The vulnerability is particularly dangerous because it can be exploited remotely without authentication.

📋 TL;DR

CVE-2023-31729 is a command injection vulnerability in TOTOLINK A3300R routers that allows attackers to execute arbitrary commands on the device via the /cgi-bin/cstecgi.cgi endpoint. This affects users running vulnerable firmware versions, potentially giving attackers full control over the router. The vulnerability is particularly dangerous because it can be exploited remotely without authentication.

💻 Affected Systems

Products:

TOTOLINK A3300R

Versions: v17.0.0cu.557

Operating Systems: Embedded Linux

Default Config Vulnerable: ⚠️ Yes

Notes: The vulnerable CGI endpoint is typically accessible via web interface. No special configuration needed for exploitation.

📦 What is this software?

A3300r Firmware by Totolink

View all CVEs affecting A3300r Firmware →

⚠️ Risk & Real-World Impact

🔴

Worst Case

Complete compromise of the router allowing attackers to intercept all network traffic, install persistent backdoors, pivot to internal networks, or use the device for botnet activities.

🟠

Likely Case

Remote code execution leading to router takeover, credential theft, DNS hijacking, and network surveillance.

🟢

If Mitigated

Limited impact if the router is behind strict firewall rules, not internet-facing, and network segmentation prevents lateral movement.

🌐 Internet-Facing: HIGH - The vulnerability is remotely exploitable without authentication, making internet-facing routers immediate targets.

🏢 Internal Only: MEDIUM - Internal attackers or compromised internal systems could exploit this, but requires network access.

🎯 Exploit Status

Public PoC: ⚠️ Yes

Weaponized: LIKELY

Unauthenticated Exploit: ⚠️ Yes

Complexity: LOW

Public proof-of-concept code exists on GitHub. The exploit requires sending crafted HTTP requests to the vulnerable endpoint.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Unknown

Vendor Advisory: http://totolink.com

Restart Required: Yes

Instructions:

1. Check TOTOLINK website for firmware updates. 2. Download latest firmware. 3. Access router admin interface. 4. Navigate to firmware upgrade section. 5. Upload and apply new firmware. 6. Reboot router.

🔧 Temporary Workarounds

Block CGI endpoint access

linux

Use firewall rules to block access to the vulnerable /cgi-bin/cstecgi.cgi endpoint

iptables -A INPUT -p tcp --dport 80 -m string --string "/cgi-bin/cstecgi.cgi" --algo bm -j DROP
iptables -A INPUT -p tcp --dport 443 -m string --string "/cgi-bin/cstecgi.cgi" --algo bm -j DROP

Disable web management interface

all

Turn off the router's web management interface if not needed

🧯 If You Can't Patch

Isolate the router in a separate network segment with strict firewall rules
Implement network monitoring for suspicious requests to /cgi-bin/cstecgi.cgi

🔍 How to Verify

Check if Vulnerable:

Check firmware version in router admin interface or via command: curl -s http://router-ip/ | grep -i firmware

Check Version:

curl -s http://router-ip/ | grep -i 'firmware\|version'

Verify Fix Applied:

Verify firmware version is updated beyond v17.0.0cu.557 and test if /cgi-bin/cstecgi.cgi endpoint still accepts malicious payloads

📡 Detection & Monitoring

Log Indicators:

HTTP requests to /cgi-bin/cstecgi.cgi with shell metacharacters
Unusual command execution in router logs
Multiple failed login attempts followed by CGI access

Network Indicators:

HTTP POST requests to /cgi-bin/cstecgi.cgi containing pipe characters, semicolons, or backticks
Unusual outbound connections from router

SIEM Query:

source="router_logs" AND (uri_path="/cgi-bin/cstecgi.cgi" AND (content="|" OR content=";" OR content="`"))

📊 Metadata

CVE ID: CVE-2023-31729

CVSS v3 Score: 9.8 (CRITICAL)

CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CWE: CWE-77

Published: May 18, 2023

Last Updated: January 22, 2025

🔗 References

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