Misusing Digital Certificates

Pierluigi Paganini July 29, 2014

Excerpt from the post “How Cybercrime Exploits Digital Certificates” which details means and motivation of illicit activities which abuses digital certificates.

Digital certificates have been misused many times during recent years. Bad actors abused them to conduct cyber attacks against private entities, individuals and government organizations. The principal abuses of digital certificates observed by security experts:

Man-in-the-middle (MITM) attacks

Bad actors use digital certificates to eavesdrop on SSL/TLS traffic. Usually these attacks exploit the lack of strict controls by client applications when a server presents them with an SSL/TLS certificate signed by a trusted but unexpected Certification Authority.

SSL certificates are the privileged mechanism for ensuring that secure websites really are who they say they are. Typically, when we access a secure website, a padlock is displayed in the address bar. Before the icon appears, the site first presents a digital certificate, signed by a trusted “root” authority, that attests to its identity and encryption keys.

Unfortunately web browsers, due to improper design and lack of efficient verification processes, accept the certificates issued by the trusted CA, even if it is an unexpected one.

An attacker that is able to obtain a fake certificate from any certification authority and present it to the client during the connection phase can impersonate every encrypted web site the victim visits.

“Most browsers will happily (and silently) accept new certificates from any valid authority, even for web sites for which certificates had already been obtained. An eavesdropper with fake certificates and access to a target’s internet connection can thus quietly interpose itself as a ‘man-in-the-middle’, observing and recording all encrypted web traffic traffic, with the user none the wiser.”

Digital Certificates 1

Cyber attacks based on signed malware

Another common cyber attack is based on malware signed with stolen code-signing certificates. The techniques allow attackers to improve avoidance techniques for their malicious codes. Once the private key associated with a trusted entity is compromised, it could be used to sign the malicious code of the malware. This trick allows an attacker to also install those software components (e.g. drivers, software updates) that require signed code for their installation/execution. One of the most popular cases was related to the data breach suffered by security firm Bit9. Attackers stole one of the company’s certs and used it to sign malware and serve it. The certificate was used to sign a malicious Java Applet that exploited a flaw in the browser of targeted browser.

Malware installed illegitimate certificates

Attackers could use also malware to install illegitimate certificates to trust them, avoiding security warnings. Malicious code could for example operate as a local proxy for SSL/TLS traffic, and the installed illegitimate digital certificates could allow attackers to eavesdrop on traffic without triggering any warning. The installation of a fake root CA certificate on the compromised system could allow attackers to arrange a phishing campaign. The bad actor just needs to set up a fake domain that uses SSL/TLS and passes certificate validation steps. Recently, Trend Micro has published a report on a hacking campaign dubbed “Operation Emmental”, which targeted Swiss bank accounts with a multi-faceted attack that is able to bypass two factor authentication implemented by the organization to secure its customers. The attackers, in order to improve the efficiency of their phishing schema, used a malware that installs a new root Secure Sockets Layer (SSL) certificate, which prevents the browser from warning victims when they land on these websites.

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CAs issued improper certificates

Improper certificates are issued by the CAs and hackers use them for cyber attacks. In one of the most blatant cases, DigiCert mistakenly sold a certificate to a non-existent company. the digital certificate was then used to sign malware used in cyber attacks.

Read the Full Article “How Cybercrime Exploits Digital Certificates”  on the Infosec Institute.

Pierluigi Paganini

Security Affairs –  (Digital Certificates, cybercrime)

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