Security researchers have identified a concerning resurgence in the online infrastructure activity of APT-C-35, a sophisticated threat group also known as DoNot. This India-based actor, widely recognized as a state-sponsored entity with a focus on espionage in South Asia, continues to leverage distinctive technical markers to maintain its command-and-control channels. The latest findings highlight how APT-C-35’s infrastructure activity employs specific Apache HTTP response indicators that are now being utilized for detection and monitoring by cybersecurity professionals.
The persistent threat posed by APT-C-35 to government, defense, and diplomatic organizations remains a significant concern. Their operational methods, characterized by an ability to evade traditional detection, are being further illuminated by the analysis of their web server configurations. These recent disclosures provide critical intelligence on how the group establishes and maintains its digital footprint across the internet, offering new avenues for defensive strategies against this persistent threat actor.
At-Bay analyst and researcher Idan Tarab spearheaded the identification of specific technical traits that differentiate APT-C-35’s web servers from legitimate ones. These distinctive markers, rooted in the characteristics of Apache HTTP responses, have proven instrumental in tracking the group’s recent activities and understanding their operational methodologies across various network segments. This intelligence is vital for cybersecurity teams aiming to proactively identify and mitigate risks associated with the DoNot group.
Infrastructure Hunting and Detection Methods for APT-C-35
The investigation into APT-C-35’s infrastructure relied on a methodical approach that combined an analysis of Apache HTTP response characteristics with data from Autonomous System Number (ASN) 399629. Cybersecurity researchers observed consistent patterns within the HTTP responses emanating from the targeted infrastructure, noting specific header configurations that served as reliable detection signatures. These signature patterns allow for the distinct identification of malicious infrastructure.
Through targeted hunting queries, researchers discovered that servers associated with APT-C-35 consistently returned specific Apache HTTP headers. These headers included standardized expiration dates and content-length values. Notably, a key indicator identified was the presence of HTTP responses with “Expires: Thu, 19 Nov 1981 08:52:00 GMT” alongside “HTTP/1.1 200 OK” status codes within ASN 399629. This specific combination significantly refined the search for APT-C-35 assets and reduced the scope of the investigation.
The analysis successfully uncovered approximately 73 results, which translated to 36 unique IP addresses within the identified infrastructure cluster. The primary server linked to this activity, gilbertfix.info, hosted on IP address 149.248.76.43 in Wyoming, exhibited typical cache control headers, including configurations like “Cache-Control: no-store, no-cache, must-revalidate.” These defensive measures suggest that the infrastructure was intentionally designed to prevent caching of information and to secure sensitive communications, a common tactic for threat actors.
The critical insight derived from this research is the enablement of proactive threat detection for security teams. By monitoring for these specific HTTP response patterns, organizations can now more effectively identify potential APT-C-35 infrastructure. This capability allows for the correlation of network indicators of compromise with known APT-C-35 infrastructure, thereby accelerating incident response times and enhancing the accuracy of threat characterization. This research underscores the vital role of continuous infrastructure hunting in maintaining operational awareness against state-sponsored threat actors like APT-C-35.
Looking ahead, the continued monitoring of these specific Apache HTTP response indicators will be crucial for tracking the evolving infrastructure of APT-C-35. Cybersecurity professionals will aim to broaden the scope of identified indicators and understand any shifts in the threat group’s operational tactics. The persistent nature of these threat actors means that ongoing vigilance and adaptation of detection strategies will be essential in mitigating their espionage activities targeting critical sectors in South Asia.