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attack-surface.md

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Attack Surface Analysis for skywind3000/kcp

Attack Surface: Source IP Spoofing (Due to UDP)

  • Description: An attacker forges the source IP address of KCP packets.
    • KCP Contribution: KCP is built on top of UDP, which is inherently connectionless and vulnerable to source IP spoofing. KCP's conv ID does not provide authentication.
    • Example: An attacker spoofs a trusted server's IP to send malicious KCP packets to clients.
    • Impact: Data breaches, unauthorized access, man-in-the-middle attacks, denial of service.
    • Risk Severity: Critical
    • Mitigation Strategies:
      • Application-Layer Authentication is Mandatory: KCP cannot mitigate this on its own. The application must implement strong cryptographic authentication (PSK or public-key based) and associate the KCP conv ID with an authenticated session. This is not a KCP-level mitigation, but it's the only way to address this inherent UDP vulnerability.

Attack Surface: Denial of Service (DoS) via Packet Flooding

  • Description: An attacker sends a large volume of KCP packets (valid or invalid, but conforming to the basic KCP packet structure) to overwhelm resources.
    • KCP Contribution: KCP's reliability and congestion control mechanisms, while designed for performance, can be abused by a flood of packets, even if those packets are ultimately rejected by the application layer. The KCP library itself must still process these packets to some extent.
    • Example: An attacker floods the server with KCP SYN packets or data packets with invalid application-layer data, consuming CPU and memory within the KCP library's processing routines.
    • Impact: Service unavailability, performance degradation.
    • Risk Severity: High to Critical
    • Mitigation Strategies:
      • KCP Configuration: Configure KCP with reasonable limits on buffer sizes, maximum connections, and other relevant parameters. This limits the resources KCP itself can consume.
      • Application-Layer Rate Limiting (Pre-KCP): Implement strict rate limiting before packets reach the KCP processing logic. This is crucial to prevent KCP's internal mechanisms from being overwhelmed. This is technically an application-layer mitigation, but it's essential for protecting KCP.
      • Firewalling: If possible, use firewall rules to restrict UDP traffic to known/trusted sources.

Attack Surface: Fragmentation/Reassembly Attacks (Targeting KCP Implementation)

  • Description: An attacker sends malformed or overlapping KCP fragments specifically crafted to exploit vulnerabilities within KCP's fragmentation and reassembly logic.
    • KCP Contribution: This attack directly targets the internal implementation of KCP's fragmentation and reassembly handling.
    • Example: An attacker sends overlapping fragments with carefully crafted header values designed to trigger a buffer overflow or other memory corruption vulnerability within the KCP library code itself.
    • Impact: Potential code execution within the context of the application (if a vulnerability exists in KCP), denial of service, data corruption.
    • Risk Severity: High
    • Mitigation Strategies:
      • Keep KCP Updated: This is the primary mitigation. Regularly update to the latest version of the KCP library to receive security patches that address any discovered vulnerabilities in its fragmentation handling.
      • Contribute to KCP Security Audits: If possible, participate in or contribute to security audits and code reviews of the KCP library, focusing on the fragmentation and reassembly code.
      • Fuzzing (of KCP itself): Ideally, the KCP library itself should be fuzzed to identify potential vulnerabilities in its handling of malformed fragments. This is a mitigation for the KCP developers, but benefits all users.

Attack Surface: Replay Attacks

  • Description: An attacker captures and re-sends valid KCP packets to cause unintended actions.
    • KCP Contribution: KCP provides reliable, ordered delivery but does not inherently prevent replay attacks. It's the application's responsibility to handle this.
    • Example: Capturing a valid data packet and replaying it multiple times.
    • Impact: Data corruption, unintended state changes, potential denial of service.
    • Risk Severity: High
    • Mitigation Strategies:
      • Application-Layer Protections are Mandatory: KCP cannot mitigate this. The application must implement sequence numbers, timestamps, and/or cryptographic nonces within the application data to detect and reject replayed packets.