Thursday, December 28, 2006

Applying the formula

Sylvan von Stuppe published a pair of excellent posts speaking about how we as security practitioners can motivate "the business" to improve the current state of web application security. Sylvan adds to my earlier list of questions with something very insightful.

"Once flaws have been identified, what is my motivation to fix them? If you can't give me the likelihood of attack, and what I stand to lose by it being exploited, how many dollars should I invest to repairing it?"

As security practitioners, we continue to say how much the development environments need to learn to make secure software. I'd say there's another side to that coin - security practitioners need to be able to measure the impact of particular threats in terms of dollars so that we don't just reveal vulnerabilities and the threats that might exploit them, but what the business stands to lose of the vulnerability isn't fixed.

Very well stated and got me thinking about how this could be done. For some reason the movie Fight Club popped into my head with the scene about how Jack, as a automative manufacture recall coordinator, applied "the formula". Seemed like a fun way to go about it. :)

I'm a recall coordinator. My job is to apply the formula.



Take the number of vehicles in the field, (A), and multiply it by the probable rate of failure, (B), then multiply the result by the average out-of-court settlement, (C). A times B times C equals X...

If X is less than the cost of a recall, we don't do one.


Are there a lot of these kinds of accidents?


Oh, you wouldn't believe.


... Which... car company do you work for?


A major one.

I know I know, I broke the first rule of Fight Club. Anyway, I have no idea how "real" this formula is or if its applied, but it seemed to make sense. I wondered if something similar could be applied to web application security. And if nothing else, an entertaining exercise.

Take the number of known vulnerabilities in a website, (A), and multiply it by the probability of malicious exploitation, (B), then multiply the result by the average average financial cost of handling a security incident, (C). A times B times C equals X...

If X is less than the cost fixing the vulnerabilities, we won't.

Sounds like it could work given you could be somewhat accurate in filling in the variables, which is the hard part. The thing is this process probably isn't a suitable task for an information security person. Maybe we need to seek the assistance of an economist of a probability theorist and see what they have to say.


Anonymous said...

Anyone have resources they use for filling in those blanks in the formula (probability of exploitation, financial cost of an attack)?

I work for a small company whose current policy towards application security is "If the client isn't asking for it (or willing to pay for it) and we haven't been hit, then it's not really a problem". I've been trying to quantify the risks in this kind of a monetary formula, but have had a very hard time finding sources I can point to when backing up my assertions that our problems with security are likely to be exploited and have the potential for very significant financial fallout.

Any info is much appreciated!

Anonymous said...

I've gotten into the habit of using this formula:

Risk (R) = Assets (A) * Vuln (V) * Threats (T)

Although technically it should be AVT divided by countermeasures.

For example, if your asset is high value, a countermeasure can be a backup copy. That makes a particular asset far less valuable in terms of availability. Likewise, encryption is a countermeasure to reduce the value in terms of confidentiality.

By splitting out V and T, it gives some measure of distinguishing between the "oh no" vulns in a vacuum and those exposed to the public or automated attacks (worms), etc.

Ranking T is tough, so I try to avoid granularity unless I have supporting data. For example, you can rate known live worms as high threats (they're always out there scanning away), known successful live attacks as high to moderate (has a motive factor that's hard to estimate, but scripted/copycat attacks are common), and so forth.

Jeremiah Grossman said...


Unfortunately I think the reason you haven't found any is because I don't think the exist. Maybe in 07 we can start the process of making something decent.

Jeremiah Grossman said...

Anonymous, sorry I reject your comment. Misclicked. Please post again.