Into the Dark: Unveiling Internal Site Search Abused for Black Hat SEO

Internal site Search Abuse Promotion (ISAP) is a prevalent Black Hat Search Engine Optimization (SEO) technique, which exploits the reputation of abused internal search websites with minimal effort. However, ISAP is underappreciated and not systematically understood by the security community. To shed light on ISAP risks, we established a collaboration with Baidu, a leading search engine in China. The key challenge of efficiently detecting ISAP risks stems from the sheer volume of daily search traffic, which involves billions of URLs. To address these efficiency bottlenecks, we introduced a first-of-its-kind lightweight detector utilizing a funnel-like approach, tailored to the unique characteristics of ISAP. This approach allows us to single out 3,222,864 ISAP URLs from 10,209 abused websites from Baidu's traffic data. We found that the businesses most likely to fall prey to this practice are porn and gambling, with two emerging areas: self-promotion for SEO and promotion for anonymous servers. By analyzing Baidu's search logs, we discovered that these malicious websites had reached millions of users in just 4 days. We further evaluated this threat on Google and Bing, thereby confirming the widespread presence of ISAP across various search engines. Moreover, we responsibly disclosed the issue to affected search engines and websites, and actively helped them fix it. In summary, our findings highlight the widespread impact and prevalence of ISAP, emphasizing the urgent need for the security community to prioritize and address such risks.