CVE-2023-30310

Executive Summary

CVE-2023-30310 identifies a critical vulnerability in the Comfast CF-616AC router that allows an unauthenticated, network-adjacent attacker to hijack TCP sessions, leading to a denial of service (DoS) condition. The vulnerability stems from improper handling of TCP state transitions, enabling an attacker to inject spoofed packets that reset or hijack active connections. This can cause service disruption for all users behind the router. No official patch has been released by Comfast, and no public proof-of-concept (PoC) code or exploit is currently available. The EPSS score is 0.0%, indicating low exploitation activity in the wild, but the lack of a patch makes this a persistent risk for affected devices.

Supply Chain & Package Security

This vulnerability is not related to any software package manager (NPM, PyPI, Go, Ruby). It is a hardware/firmware issue in the Comfast CF-616AC router.

CVSS Breakdown & Threat Level

The CVSS score is listed as 0.0, which is likely a placeholder. Based on the description and impact, a reasonable CVSS v3.1 vector would be:

• Attack Vector (AV): Adjacent Network (A) – attacker must be on the same local network.
• Attack Complexity (AC): Low (L) – no special conditions required.
• Privileges Required (PR): None (N) – no authentication needed.
• User Interaction (UI): None (N) – no user action required.
• Scope (S): Unchanged (U) – the vulnerable component is the router itself.
• Confidentiality (C): None (N) – no data exposure.
• Integrity (I): Low (L) – session hijacking can alter data in transit.
• Availability (A): High (H) – DoS impact is severe.

Estimated CVSS Vector: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H Estimated Base Score: 6.5 (Medium)

Threat Level: Medium. The attack requires adjacency to the network, but no authentication. The impact is primarily availability, with minor integrity concerns.

Deep Dive & Mechanics

The Comfast CF-616AC router runs a proprietary embedded Linux firmware. The vulnerability lies in the TCP/IP stack implementation, specifically in how the router processes TCP segments with spoofed sequence numbers. An attacker on the same local network can send crafted TCP packets that appear to belong to an existing session between a legitimate client and a server (e.g., a web server). By manipulating the sequence and acknowledgment numbers, the attacker can:

1. Reset the connection: Send a TCP RST (reset) packet, causing the router to terminate the session.
2. Inject data: Send forged data packets that the router accepts as part of the legitimate stream, potentially altering responses or injecting malicious content.

The root cause is a lack of proper TCP state validation. The router does not verify that incoming packets match the expected sequence numbers of established connections, allowing an attacker to inject packets that are accepted as valid.

Vulnerable vs. Patched Code

Since no patch is available, a direct code comparison is not possible. However, the vulnerable behavior can be described:

Vulnerable (Current Firmware):

• The router accepts TCP packets without validating the sequence number against the expected window.
• No mechanism to detect or prevent TCP session hijacking.

Patched (Hypothetical):

• Implement RFC 5961 (Improving TCP's Robustness to Blind In-Window Attacks) to validate sequence numbers.
• Add rate limiting for RST packets.
• Use TCP timestamps to detect spoofed packets.

Exploitation & Lab Setup

Red Team (Attack Simulation)

Prerequisites:

• Attacker machine on the same LAN as the target Comfast CF-616AC router.
• A tool like scapy (Python) or hping3 to craft raw TCP packets.
• Knowledge of an active TCP session (e.g., a client browsing a website).

Exploitation Steps:

1. Identify an active session: Use tcpdump or Wireshark to capture traffic and identify a TCP connection (e.g., client IP: 192.168.1.100, server IP: 203.0.113.5, ports: 12345 -> 80).
2. Craft a spoofed RST packet: Using scapy:

   from scapy.all import *
   ip = IP(src="203.0.113.5", dst="192.168.1.100")
   tcp = TCP(sport=80, dport=12345, flags="R", seq=1000)  # seq must be within window
   pkt = ip/tcp
   send(pkt)
   

3. Observe DoS: The client's connection is terminated, causing service disruption.

Note: No public exploit code exists; this is a theoretical approach.

Blue Team (Defense & Detection)

Defensive Measures:

• Network Segmentation: Isolate IoT devices like routers on a separate VLAN.
• TCP Stack Hardening: If possible, update firmware to a version that implements RFC 5961.
• Intrusion Detection: Deploy network-based IDS (e.g., Suricata) to detect anomalous TCP packets.

Detection Rules:

• Monitor for excessive TCP RST packets from unexpected sources.
• Alert on TCP packets with sequence numbers outside the expected window.

Indicators of Compromise (IOCs)

• Network Traffic:

  • High volume of TCP RST packets from a single source.
  • TCP packets with sequence numbers that do not match the expected window.
  • Spoofed source IP addresses in TCP segments.

• System Logs:

  • Router logs showing repeated connection resets.
  • Client-side logs showing "Connection reset by peer" errors.

• File Hashes:

  • No specific file hashes; this is a network-level vulnerability.

Detection Engineering

YARA Rule

rule Detect_TCP_Session_Hijack_Attempt {
    meta:
        description = "Detects potential TCP session hijacking packets targeting Comfast routers"
        author = "Valters IT"
        date = "2024-01-01"
        reference = "CVE-2023-30310"
    strings:
        $tcp_rst = { 00 00 00 00 00 00 08 00 45 00 }  // Example: IP header + TCP RST flag
    condition:
        $tcp_rst at 0
}

Sigma Rule

title: TCP Session Hijacking Attempt Against Comfast Router
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects anomalous TCP RST packets that may indicate session hijacking
author: Valters IT
logsource:
    category: network
    product: suricata
detection:
    selection:
        event_type: alert
        alert.signature_id: 2023001
    condition: selection
falsepositives:
    - Legitimate TCP resets due to network errors
level: medium

Suricata Rule

alert tcp any any -> any any (msg:"CVE-2023-30310 - Potential TCP Session Hijacking"; flow:to_client; flags:R; seq:0; threshold:type both, track by_src, count 10, seconds 60; sid:2023001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Isolate the device: Place the Comfast CF-616AC router on a separate VLAN with strict access controls.
2. Monitor network traffic: Use IDS/IPS to detect and block anomalous TCP packets.
3. Disable unnecessary services: If possible, disable remote management and other services that increase attack surface.

Long-Term Solutions:

• Replace the device: Since no patch is available, consider replacing the router with a vendor that provides security updates.
• Vendor contact: Attempt to contact Comfast for a firmware update; if unresponsive, escalate to CERT/CC or local cybersecurity authorities.

Workarounds:

• Firewall rules: Block inbound TCP RST packets from untrusted sources.
• TCP timestamps: Enable TCP timestamps on clients to help detect spoofed packets (though this is not a complete fix).

Valters IT