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Encryption and cryptography have long been thought of as the exemplars of Internet security. Unfortunately, this is not the case anymore. Encryption keys and digital certificates have become the weakest link in most organizations’ security strategies, resulting in diminished effectiveness of other security investments like NGFW, IDS/IPS, WAF, AV, etc.
In my previous post, I discussed the difference between key management and key security. The problem today is not that encryption and cryptography are broken, but rather that there are mediocre implementations to secure and protect keys and certificates from theft. Worse yet, most organizations cannot even tell the difference between rogue and legitimate usage of keys and certificates on their networks or stop attackers from using them. Bad actors and nation states continue to abuse the trust that most have in encryption, but very few in the security industry are actually doing something about it.
Undermining Your Critical Security Controls
The threatscape has changed:
- Gartner estimates by 2017, 50% of all network attacks will use SSL.
- McAfee, shows in its 2014 first quarter threat report the use of stolen certificates to sign malware continues to increase at a rate of nearly 50% quarter over quarter since 2012.
- Kaspersky Labs this year discovered multi-year APT campaigns, like Carreto and Windigo, stealing SSL and SSH keys.
- Over 90% of externally-facing servers impacted by Heartbleed have not been fully remediated.
- IBM X-Force is still seeing over 7,000 attacks per day against its customers using the Heartbleed vulnerability.
Even with all the advances in security technology over the last decade, cybercriminals are still very successful at stealing your data. The challenge is that security technologies are still designed to trust encryption. When threats use encryption, they securely bypass other security controls and hide their actions. Let’s review an example of how a bad actor can use keys and certificates to subvert any security technology or control.
Using Keys and Certificates throughout the Attack Chain
The use of keys and certificates in APT campaigns is cyclical. A typical trust-based attack can be broken up into four primary steps that include the theft of the key, use of the key, exfiltration of data, and expansion of its foothold on the network.
Step 1: Steal the Private Key
When Symantec analyzed sample malware designed to steal private keys from certificate stores, the same behavior was noted for every malware variant that was studied. In this current example, the CertOpenSystemStoreA function is used to open stored certificates, and the PFXExportCertStoreEx function exports the following certificate stores:
- MY: A certificate store that holds certificates with the associated private keys
- CA: Certificate authority certificates
- ROOT: Root certificates
- SPC: Software Publisher Certificates
The malware samples were able to steal the digital certificate and corresponding private key by performing the following actions:
- Opens the MY certificate store
- Allocates 3C245h bytes of memory
- Calculates the actual data size
- Frees the allocated memory
- Allocates memory for the actual data size
- The PFXExportCertStoreEx function writes data to the CRYPT_DATA_BLOB area to which the pPFX points
- Writes data (No decryption routine is required when it writes the content of the certificate store)
Step 2: Use the Key
With access to the private key, there are a multitude of use cases for a malicious campaign. Let’s review how cybercriminals impersonate a website and sign malware with a code-signing certificate.
Website impersonation can easily be achieved using the stolen private key as part of a spear-phishing campaign. The attacker sets up a clone version of the target website—Outlook Web Access (OWA) or a company portal would be a prime target. By using the stolen private key and certificate anyone that visits the website would not see any errors in the browser. The fake website also hosts the malware that is intended for the victim.
Step 3: Exfiltrate the Data
Now that the fake website is prepped and ready to go, it’s time to execute the spear-phishing campaign. Using popular social networks like LinkedIn, it is a simple process to profile a victim and formulate a well-crafted email that will entice the victim to click on a malicious link. Imagine you get an email from the IT administrator stating that your password will be expiring shortly, and that you need to change your password by logging into OWA. The IT administrator very kindly also provided you with a link to OWA in the email for you to click on and reset your password.
When you click on the link and input your credentials into the OWA website, not only are your credentials stolen, but malware is installed onto your machine. It’s important to note that the malware is also signed using a stolen code-signing certificate to avoid detection. By signing the malware with a legitimate code-signing certificate the attackers increase their chances of avoiding detection.
In part 2 of this blog series, I will cover step 4 and discuss some examples of the actions trust-based threats perform and how bad actors use keys and certificates to maintain their foothold in the enterprise network. I will also offer some guidance on how to mitigate trust-based attacks.