Critical Security Flaw Exposes V2Ray, Xray, and Clash Users to Exploitation

A significant security vulnerability affecting V2Ray, Xray, and Clash proxy users has been identified, potentially allowing malicious actors to leverage exposed proxies as intermediaries for illicit activities. This flaw stems from deviations from RFC standards in the implementation of SOCKS protocols, creating opportunities for unauthorized access and exploitation.

The Exposure: How Proxies Are Compromised

Many users, particularly those with soft routers or VPS setups using X-UI, inadvertently expose their SOCKS proxies to the public internet. While some users implement password authentication for their SOCKS proxies, this measure can be easily bypassed due to the aforementioned protocol flaws.

Network vulnerability scanner running on a laptop screen, displaying a list of open ports and potential vulnerabilities.

Here’s how the vulnerability can be exploited:

Public Exposure: SOCKS proxies are unintentionally made accessible over the public internet.
Bypass Authentication: Attackers bypass password authentication mechanisms due to flaws in V2Ray, Xray, and Clash’s SOCKS implementation.
Relay and Hijacking: Attackers relay their traffic through the compromised proxies, effectively using them as “stepping stones” for malicious activities.

Demonstration of the Exploit

Security researchers have demonstrated the ease with which this vulnerability can be exploited. By scanning for publicly exposed Clash users, attackers can identify vulnerable proxies. A Python script can be used to scan for open Clash SOCKS ports, revealing a large number of exploitable IPs.

Hacker using multiple screens in a dimly lit room, lines of code displayed on one screen, network diagrams on another.

The exploit involves:

Scanning public networks for exposed Clash instances.
Identifying open SOCKS proxy ports (e.g., 7891).
Configuring a local Clash instance to forward UDP traffic to the target proxy.
Effectively routing traffic through the victim’s proxy without proper authorization.

Technical Deep Dive: The SOCKS Protocol Deviation

The root cause lies in the non-standard implementation of the SOCKS protocol in V2Ray, Xray, and Clash. According to RFC specifications, a SOCKS proxy, upon successful TCP authentication, should dynamically allocate a random UDP port for subsequent UDP traffic. However, these implementations often use a fixed port, mirroring the TCP SOCKS port. This deviation eliminates the need for UDP authentication, allowing attackers to freely route UDP traffic through the exposed proxy.

Mitigation Strategies: Securing Your Proxy

Several steps can be taken to mitigate this security risk:

Firewall Configuration: Implement strict firewall rules to block external access to SOCKS proxy ports. Soft router users should configure their firewalls to reject incoming traffic on the WAN zone for the SOCKS port.
Port Forwarding Review: Examine port forwarding rules and disable unnecessary SOCKS port forwarding.
Consider Alternatives: Evaluate using alternative proxy solutions like Sing-box, which adheres to RFC standards for SOCKS proxy implementations.

Firewall interface displaying a list of rules, highlighting a rule blocking incoming traffic on a specific port.

Real-World Implications and Exploitation Scenarios

The vulnerability can be leveraged beyond simple proxy hijacking. Attackers can utilize the compromised UDP connection to tunnel other protocols, such as Hysteria, effectively using the victim’s proxy as a high-speed relay. Furthermore, users employing X-UI to create SOCKS proxies are particularly vulnerable, as the random port assignment can be easily scanned and exploited.

Identifying Exposure: Testing Your Proxy

Users can verify if their SOCKS proxy is exposed by:

Determining their public IP address.
Using an online port scanner to check if the SOCKS proxy port is open.

If the port is open, it indicates that the proxy is exposed and vulnerable to exploitation.

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