Using software reliability models for security assessment — Verification of assumptions

Can software reliability models be used to assess software security? One of the issues is that security problems are relatively rare under "normal" operational profiles, while "classical" reliability models may not be suitable for use in attack conditions. We investigated a range of Fedora open source software security problems to see if some of the basic assumptions behind software reliability growth models hold for discovery of security problems in non-attack situations. We find that in some cases, under "normal" operational use, security problem detection process may be described as a Poisson process. In those cases, we can use appropriate classical software reliability growth models to assess "security reliability" of that software in non-attack situations.We analyzed security problem discovery rate for RedHat Fedora. We find that security problems are relatively rare, their rate of discovery appears to be relatively constant under "normal" (non-attack) conditions. Discovery process often appears to satisfy Poisson assumption opening doors to use of classical reliability models. We illustrated using Yamada S-shaped model fit to v15 that in some cases such models may be effective in predicting the number of remaining security problems, and thus may offer a way of assessing security "quality" of the software product (although not necessarily its behavior under an attack).