[论文解读] SPAM over Internet Telephony and how to deal with it

Andreas U. Schmidt, Nicolai Kuntze+1 more|ArXiv.org|Jun 10, 2008

IPv6, Mobility, Handover, Networks, Security参考文献 6被引用 8

一句话总结

本文研究了互联网语音电话垃圾信息（SPIT），分析了现有反SPIT解决方案，并通过自定义基准测试工具SXSM（SIP XML场景生成器）揭示其漏洞，该工具可实现精确、可重复的SPIT攻击模拟，以测试系统韧性。主要贡献在于提出了一套系统性方法，通过利用实现层面的弱点，评估并改进SPIT防御机制。

ABSTRACT

In our modern society telephony has developed to an omnipresent service. People are available at anytime and anywhere. Furthermore the Internet has emerged to an important communication medium. These facts and the raising availability of broadband internet access has led to the fusion of these two services. Voice over IP or short VoIP is the keyword, that describes this combination. The advantages of VoIP in comparison to classic telephony are location independence, simplification of transport networks, ability to establish multimedia communications and the low costs. Nevertheless one can easily see, that combining two technologies, always brings up new challenges and problems that have to be solved. It is undeniable that one of the most annoying facet of the Internet nowadays is email spam. According to different sources email spam is considered to be 80 to 90 percent of the email traffic produced. The threat of so called voice spam or Spam over Internet Telephony (SPIT) is even more fatal, for the annoyance and disturbance factor is much higher. As instance an email that hits the inbox at 4 p.m. is useless but will not disturb the user much. In contrast a ringing phone at 4 p.m. will lead to a much higher disturbance. From the providers point of view both email spam and voice spam produce unwanted traffic and loss of trust of customers into the service. In order to mitigate this threat different approaches from different parties have been developed. This paper focuses on state of the art anti voice spam solutions, analyses them and reveals their weak points. In the end a SPIT producing benchmark tool will be introduced, that attacks the presented anti voice spam solutions. With this tool it is possible for an administrator of a VoIP network to test how vulnerable his system is.

研究动机与目标

• 识别并分析现有反SPIT机制在技术和实践层面的薄弱环节。
• 开发一种可复现、可配置的攻击框架，以测试SPIT防御系统的韧性。
• 展示SPIT攻击如何通过协议层操作绕过当前检测技术。
• 提供一个基准测试工具（SXSM），供系统管理员评估其VoIP网络对SPIT的脆弱性。
• 通过揭示破坏现有SPIT缓解策略的攻击向量，为未来研究提供指导。

提出的方法

• SXSM工具使用基于XML的配置文件生成并控制SIP场景，以实现对SPIT攻击的精细时间控制和呼叫速率控制。
• 该工具支持多种攻击模式，包括SIP身份伪造、账号切换、声誉操纵，以及通过第三方呼叫控制（3PCC）实现的CAPTCHA中继攻击。
• 攻击场景可按顺序或并行执行，实现对批量呼叫发起的精确模拟，且可自定义源和目标身份。
• 通过在BYE消息中注入正面声誉值，该工具可实现声誉操纵，模拟受控环境下的声誉推送或拉取。
• 通过自动化快速发送REGISTER请求以覆盖合法用户注册，该工具支持注册劫持攻击。
• 利用3PCC技术模拟CAPTCHA中继攻击，将呼叫从受害者转发至人工求解者，从而绕过自动化检测。

实验结果

研究问题

• RQ1 当前反SPIT防御机制中存在哪些关键技术与实际应用层面的漏洞？
• RQ2 如何利用标准化SIP协议系统性地生成并控制SPIT攻击？
• RQ3 现有SPIT检测机制在多大程度上可被身份伪造、声誉操纵或协议滥用所绕过？
• RQ4 SXSM工具在模拟真实SPIT攻击场景以测试VoIP安全方面有多高效？
• RQ5 哪些攻击模式（如注册劫持或CAPTCHA中继）可用于绕过反SPIT防御？

主要发现

• 现有反SPIT机制存在显著的技术与实际应用层面的弱点，可通过协议层操作加以利用。
• SXSM工具可实现对SPIT攻击的精确、可重复模拟，全面控制呼叫速率、目标列表及SIP身份来源。
• 通过外部CSV文件轮换主叫身份，SIP身份伪造与账号切换攻击可被有效执行。
• 通过在BYE消息中注入声誉值实现的声誉操纵表明，若未妥善保护，声誉系统极易受到操纵。
• CAPTCHA中继攻击可通过利用3PCC将呼叫转发至人工求解者，从而绕过自动化检测，破坏机器人检测机制。
• 通过快速发送REGISTER请求实现的注册劫持是一种可行手段，可覆盖合法用户注册并实现身份伪装。