Open source software security

Review of Chained Exploits by Whitaker, Evans and Voth

30 November -0001

I looked forward to Chained Exploits: Advanced Hacking Attacks from Start to Finish (CE) by Whitaker, Evans and Voth with much anticipation as the concept is a much needed addition to the lexicon on information security. Often academic fields are severely limited by the vocabulary available to discuss issues and the "chained exploit" is sure to become a mainstay in the discourse of information security. Despite my enthusiasm for the concept, however, I was disappointed by the material presented in CE. The genius of the chained exploit is that it upends the traditional threat matrix, typically presented as:

[value of resource] x [likelihood of exploit] = [risk level]

For example, a high value resource that is unlikely to be exploited should be ranked as a low risk, as should a low value resource that is likely to be exploited. Think of this in terms of a temporary database of publicly available information used to populate a user demonstration website that is wiped out every 24 hours. If that information is compromised it has no value, so even if the compromise is likely it is a low risk system. Conversely if a system that contains critical financial information is confined to a single workstation that is removed from any networking and housed in a guarded facility it too is a low risk system (since the likelihood of compromise is low).

Unfortunately many auditors make risk assessments based on circumstances in a vacuum. This is where the concept of "chained exploits" becomes so valuable. For instance, if a vulnerability were discovered in a local binary accessible to users that allows privilege escalation, but the local binary exists on a system that has no users (other than administrators who already have root privileges) it is often considered a low risk. Many times patches for these sorts of vulnerabilities are not installed because the patch could introduce instability and would not be considered worthy of the expense given the low risk. Similarly a vulnerability could be discovered in a web service that when exploited could allow a remote attacker to gain an unprivileged local account that, say, only had access to read and write to the /tmp directory. This could also be considered a low risk since such limited access wouldn't present any threat to the system. However, if you "chained exploits" for the two vulnerabilities you suddenly have a condition where a remote attacker can gain a local account and elevate their privilege! This contravenes the low risk ranking of the individual vulnerabilities. When combined they suddenly become a very high risk to the system.

It was this sort of "chain" that I hoped CE would explore. Instead the material presented in the book consisted of context to several high risk vulnerabilities to explain why they might be used in tandem. For instance, the book would propose a scenario where a remote attacker installed a backdoor rootkit on a corporate network workstation then used that workstation to access the central database using default system administrator credentials. Each of the conditions used in these "chains" are extremely high risk already, and thus the book doesn't present any new material for seasoned information security professionals to consider.

For a novice this book is a great resource. It is full of the sorts of horror stories that professionals are all too familiar with, but could potentially be eye opening for a neophyte or someone unfamiliar with computer security.

I was disappointed that the book didn't raise the level of discourse in the information security field but I suspect that wasn't the point of Chained Exploits. Instead it reads like a greatest hits sequence prepared by veteran penetration testers. It makes for interesting reading, but it isn't particularly informative. Don't look for any new 0 day exploits (or even a discussion of how to find such flaws). Instead the book contains a litany of well known routes to system compromise and illustrative narratives that tie them together in real world scenarios.