FIPS certification pays off

OpenSSL has a FIPS-140 validated module. One of the requirements is self-testing of the PRNG. Unfortunately, it somehow doesn't quite work
A significant flaw in the PRNG implementation for the OpenSSL FIPS Object Module v1.1.1 (, FIPS 140-2 validation certificate #733, has been reported by Geoff Lowe of Secure Computing Corporation. Due to a coding error in the FIPS self-test the auto-seeding never takes place. That means that the PRNG key and seed used correspond to the last self-test. The FIPS PRNG gets additional seed data only from date-time information, so the generated random data is far more predictable than it should be, especially for the first few calls.

This vulnerability is tracked as CVE-2007-5502.

There's no real deep lesson here. This is the kind of mistake anyone can accidentally make. It's true that the more options you have in a piece of code, the higher the chance that there will be a some code path that doesn't work right, and in this case it's particularly striking because (1) there's no need to self-test a software PRNG 1 and (2) it's the addition of the self-test that broke it, but it could have easily have been something else.

1. In general, self-testing any cryptographic PRNG is difficult. The standard way to build a CSPRNG is to take whatever your entropy source is and run it through a bunch of hash functions. The result of this is that the output looks random under standard entropy tests. This is true even if the seed is very low entropy. All a self-test really means is that the hashing part of the PRNG is working correctly, but usually it's the seeding part that goes wrong (as seen here).