Authored by Margit Hazenbroek At Fox-IT (part of NCC Group) identifying servers that host nefarious activities is a critical aspect of our threat intelligence. One approach involves looking for anomalies in responses of HTTP servers. Sometimes cybercriminals that host malicious servers employ tactics that involve mimicking the responses of legitimate software to evade detection. However, … Continue reading The Spelling Police: Searching for Malicious HTTP Servers by Identifying Typos in HTTP Responses →

Authored by Mick Koomen Summary Blister is a piece of malware that loads a payload embedded inside it. We provide an overview of payloads dropped by the Blister loader based on 137 unpacked samples from the past one and a half years and take a look at recent activity of Blister. The overview shows that … Continue reading Popping Blisters for research: An overview of past payloads and exploring recent developments →

Fox-IT (part of NCC Group) has uncovered a large-scale exploitation campaign of Citrix NetScalers in a joint effort with the Dutch Institute of Vulnerability Disclosure (DIVD). An adversary appears to have exploited CVE-2023-3519 in an automated fashion, placing webshells on vulnerable NetScalers to gain persistent access. The adversary can execute arbitrary commands with this webshell, … Continue reading Approximately 2000 Citrix NetScalers backdoored in mass-exploitation campaign →

Authored by Edwin van Vliet and Max Groot One year ago, Fox-IT and NCC Group released their blogpost detailing findings on detecting & responding to exploitation of CVE-2021-44228, better known as ‘Log4Shell’. Log4Shell was a textbook example of a code red scenario: exploitation was trivial, the software was widely used in all sorts of applications … Continue reading One Year Since Log4Shell: Lessons Learned for the next ‘code red’ →