This threat involves malware authors employing multiple digital certificates to sign their malicious software, thereby attempting to evade detection by security solutions. Digital code signing is a security mechanism that verifies the authenticity and integrity of software by using cryptographic certificates issued by trusted Certificate Authorities (CAs). Typically, security products use the presence of a valid digital signature as an indicator of trustworthiness. However, adversaries have adapted by acquiring or compromising multiple legitimate digital certificates and using them to sign malware binaries. This tactic complicates detection efforts because the malware appears to be signed by different trusted entities, making it harder for signature-based and reputation-based security tools to flag the files as malicious. The use of multiple certificates can also help malware authors bypass blacklists that rely on certificate identifiers. Although the provided information does not specify particular malware families or affected software versions, the technique itself represents a sophisticated evasion method that can be applied across various malware types and delivery vectors. The threat was reported by CIRCL in 2016 and categorized as medium severity, indicating a moderate level of risk. No known exploits in the wild were documented at the time, but the technique remains relevant as digital certificate abuse continues to be a common tactic in malware campaigns.

For European organizations, this threat poses a significant challenge to endpoint security and malware detection capabilities. Organizations relying heavily on signature-based detection or reputation services may experience increased false negatives, allowing malware to execute undetected. This can lead to unauthorized access, data exfiltration, disruption of services, or lateral movement within networks. The abuse of digital certificates undermines trust in software supply chains and complicates incident response efforts, as it becomes more difficult to distinguish legitimate software from malicious payloads. Critical sectors such as finance, healthcare, and government institutions in Europe could be particularly impacted due to their reliance on trusted software and stringent regulatory requirements around data protection and system integrity. Additionally, the presence of multiple certificates may delay detection and remediation, increasing the window of opportunity for attackers to achieve their objectives.

European organizations should implement multi-layered security controls that do not solely rely on digital signatures for trust decisions. Practical steps include: 1) Employ advanced endpoint detection and response (EDR) solutions that analyze behavioral indicators and heuristics beyond signature validation. 2) Maintain an updated inventory of trusted certificates and monitor for unusual certificate usage or new certificates appearing in the environment. 3) Use certificate reputation services and threat intelligence feeds to identify suspicious certificates. 4) Implement strict code signing policies, including restricting which certificates can be used to sign executables within the organization. 5) Enforce application whitelisting and sandboxing to limit execution of unauthorized software. 6) Conduct regular audits of certificates issued to the organization and promptly revoke any compromised certificates. 7) Educate security teams on the risks of certificate abuse and incorporate this threat into incident response playbooks. 8) Collaborate with certificate authorities and industry groups to report and respond to certificate misuse.