When we talk about âthe next Heartbleedâ we have to consider that new vulnerabilities are discovered every day and that many of them are just as widespread as Heartbleed. To put some bounds on this lets define a âsupercriticalâ vulnerability that would have similar impact to Heartbleed as one that meets all of the following 4 criteria (all of which Heartbleed does meet):
â¢ Affects software that is in widespread use as an Internet-facing service that commonly handles sensitive data
â¢ Is present in version(s) of that software representing a sizable percentage of the deployed base
â¢ Can be exploited to reveal sensitive information (directly or indirectly) without logging in with a valid username and password
â¢ Its method of exploitation is widely known
This definition narrows things down very quickly simply because there are only two types of services that can reasonably meet the first criteria: web servers and email. Over the past decade many of the services that would previously have existed as client/server applications with their own protocols have been migrated to web-based applications and over the past few years these web-based applications have begun a steady migration to a handful of cloud-based service providers, often running homogenous environments. We are increasingly putting more eggs in fewer and fewer baskets which increases the potential for damage if one of those baskets is found to be vulnerable. The only widespread service to buck this web consolidation trend, at least in some part, and remain as a standalone service is corporate email that still relies on the SMTP protocol for transport. Personal email accounts are in double-jeopardy as the front-ends have very much moved to web-based services like Gmail, YahooMail, and Hotmail but these services still rely on the same basic underlying SMTP protocol for mail transport as corporate email systems making them vulnerable to attack from either angle.
We also have to remember that there are other protocols and pieces of software that underpin the frontend web and email services. These include encryption technologies, like the OpenSSL software that was affected by Heartbleed, as well as the operating system software itself. Pretty much the worst thing imaginable (much worse than Heartbleed) would be an arbitrary code execution vulnerability in the TCP/IP stack (the chunk of the operating system software that controls all network communications) of a widely used version (or versions) of a common server operating system like Windows, Linux, or FreeBSD. This would let an attacker take complete control of any affected system that can be reached from the Internet, likely regardless of what services it is or is not running.
Defending against these sorts of vulnerabilities is a daunting task for the IT administrator who is responsible for securing systems running software that he has no control of while keeping those services available even in the face of potential zero-day vulnerabilities. There are some basic rules that can be used to drastically reduce the risk:
Less software is better: Unfortunately most default software installs come with every possible package and option installed and enabled. Every piece of software contains vulnerabilities, some just havenât been found yet, and every piece of software and functionality that gets installed and enabled exposes more of these potential vulnerabilities (even security software like OpenSSL, antivirus, and firewalls). Any unnecessary packages that are disabled, removed, or not installed in the first place will decrease the chances that a particular system is affected by the next big vulnerability.
Reduce privileges: Administrators have a bad habit of running software as a privileged account such as root, a local administrator, or a domain administrator. Similarly software developers and database administrators have a bad habit of using accounts with full read/write access to entire databases (or in some cases entire database servers containing multiple unrelated databases) for interaction between a web-based fronted and a database backend. These practices are convenient as they eliminate the need to consider user access controls but the consequence is that an attacker will gain these same unlimited privileges if he manages to exploit a vulnerability. The better security practice is to create dedicated accounts for each service and application that have the bare minimum access required for the software to function. It may not stop an attacker but it will limit the amount of immediate damage he can cause and provide the opportunity to stop him.
Patch: For those services that do have to stay enabled, make sure to stay on top of patches. Often times vulnerabilities are responsibly disclosed only to software vendors and patches are quietly released before the details of the vulnerability are publicly acknowledged. Administrators who proactively apply security patches will have already protected themselves while those who didnât will be in a race with attackers to apply patches before exploits are developed and used.
Firewall: The definition of a âsupercriticalâ vulnerability above includes âInternet-facingâ for a reason: it is much easier to find a vulnerable system when it can be found by scanning across the open Internet. Services intended for internal use should be restricted to access from internal systems only, and for those internal service that require access from outside consider a VPN in order to authenticate users before allowing direct access to the system. Firewalls are not an excuse to avoid patching however, as many attacks are launched across internal networks from systems already compromised by malware.
Defense in Depth: There will always be some services that must be enabled and kept exposed to the Internet that may be affected by a zero-day vulnerability for which patches are not available yet. We must then start relying on our ability to detect and stop an attack before it succeeds. Hopefully the combination of techniques described above (especially reduced privileges) will slow an attacker down enough that he becomes easier to detect. We can also increase the chances of detection by looking for the signs of an attack (such as with antivirus, intrusion detection/prevention systems, file integrity monitoring, behavior monitoring, and log correlation) while making it harder for him to exfiltrate any sensitive data (firewalling outbound connections, data loss prevention technology, proxying). We must also always have a real live human ready to quickly respond to any alerts and intervene to stop an active attack, without that all of this technology is useless and itâs just a matter of time before an attacker finds a way around it.