Operation Rewrite is a large-scale SEO poisoning campaign attributed to a Chinese-speaking threat actor group linked to previously known entities such as Group 9 and possibly DragonRank. The attackers leveraged BadIIS malware, which consists of malicious IIS modules, ASP.NET handlers, and PHP scripts, to compromise legitimate websites primarily in East and Southeast Asia, with a particular focus on Vietnam. By implanting these malicious modules into web servers running Microsoft IIS, the threat actors intercepted and manipulated web traffic to alter search engine results and redirect users to malicious or fraudulent content. This manipulation of search engine results (SEO poisoning) enables the attackers to increase the visibility of malicious sites or content, potentially leading to further exploitation such as malware distribution, credential theft, or other malicious activities. The campaign's toolkit allows injection of malicious content directly into web pages served by compromised servers, enabling stealthy and persistent manipulation without requiring user interaction beyond visiting affected sites. The use of web shells and various exploitation techniques (referenced by MITRE ATT&CK IDs T1133, T1190, T1112, T1505.003, T1078) indicates a sophisticated approach involving initial access, persistence, and credential access to maintain control over compromised infrastructure. Although no known exploits are currently reported in the wild for this specific malware, the campaign's scale and complexity demonstrate a significant threat to web infrastructure relying on IIS servers, especially those with weak patching or security controls.

For European organizations, the primary impact of Operation Rewrite lies in the potential compromise of IIS-based web servers, which could lead to unauthorized content manipulation, redirection of legitimate traffic to malicious sites, and subsequent exposure of users to malware or phishing attacks. This can damage organizational reputation, lead to data breaches, and disrupt web services. SEO poisoning can also undermine trust in search results, affecting marketing and customer acquisition efforts. Additionally, compromised servers may be used as footholds for further lateral movement or as platforms for launching additional attacks. While the campaign currently targets East and Southeast Asia, European organizations using IIS infrastructure, especially those with public-facing websites, could be targeted in future operations or collateral damage. The manipulation of web content and redirection can also lead to regulatory and compliance issues under GDPR if personal data is exposed or if users are misled. The medium severity rating reflects the complexity of exploitation and the indirect but significant consequences of compromised web infrastructure.

European organizations should implement specific mitigations beyond generic advice: 1) Conduct thorough audits of IIS servers to detect unauthorized modules or handlers, focusing on identifying unusual ASP.NET or PHP scripts that could indicate BadIIS variants. 2) Employ application whitelisting and integrity monitoring to detect unauthorized changes to web server components. 3) Harden IIS configurations by disabling unnecessary modules and enforcing strict access controls on web server file systems and configuration files. 4) Monitor web traffic for anomalies such as unexpected redirects or content injections, using web application firewalls (WAFs) with updated signatures to detect SEO poisoning patterns. 5) Implement multi-factor authentication and credential hygiene to prevent credential theft and lateral movement as indicated by T1078. 6) Regularly update and patch IIS servers and associated web applications to close vulnerabilities exploited for initial access (T1190). 7) Use threat intelligence feeds to monitor for indicators of compromise related to BadIIS and associated threat actor groups. 8) Train security teams to recognize SEO poisoning tactics and conduct incident response drills focused on web server compromises. 9) Restrict administrative access to IIS servers and monitor logs for suspicious activity related to module installation or configuration changes.