OpenVPN fuzzers released + notes

First of all a very heartfelt thanks to all those who donated in the wake of my OpenVPN findings.

Private Internet Access donated $1000! Another donor whose I identity I know is Shawn C[ a.k.a “citypw”] of HardenedLinux. An unknown person or company donated $1000 as well. And about 15 others donated too. Thank you so much! Very inspiring and your generous tokens of appreciation mean a lot to me. UPDATE: IPredator donated $7500! Wow.

I’ve uploaded my fuzzers here.

Maybe you think that OpenVPN has now been completely X-rayed by fuzzers; this is not the case.  There are still signification portions of the code that are left to explore. It wouldn’t surprise me at all if more vulnerabilities emerge. This requires that more fuzzers are written for specific parts (for example all the code in ssl.c !). I have disabled some ASSERTs and other code because they crash the fuzzer, for example here, and it requires more research to determine whether these asserts are reachable remotely. The fuzzing framework + IO abstractions I have published will make the creation of more fuzzers a relatively easy effort, as long as you know what you are doing (set variables passed to a function to sane values, comment out code where applicable, etc).

If you find more vulnerabilities, report them to security@openvpn.net before you disclose them and enjoy your bragging rights and maybe a bounty from OSTIF.

There appears to be an impression that I’m in favor of abolishing manual code reviews. This is not true. In fact, I listed several types of vulnerabilities that cannot be found with fuzzers. All I’m saying is to be aware of the respective strengths and weakness of each strategy, and to use a sensible approach to find vulnerabilities. If you have a function that takes a null-terminated a string followed by 500 lines of spaghetti code that does string operations like it’s 1983, I’d rather write a fuzzer in 3 minutes that finds 5 overflows in 5 minutes, than frying my brain for an hour to discern the logic and manually concocting input that leads to corner cases. Of course, you can still do a manual examination once the fuzzer has run its course. But a fuzzer isn’t going to detect that you’re accidentally sending your private key to the peer due to program logic gone awry, and instead requires human intelligence determine this. So the upshot is; use both, and be sensible in striking a balance.

Interestingly, the wrong method to free a GENERAL_NAMES structure is not limited to OpenVPN. By using the fantastic Debian Codesearch I discovered that the issue was also present in FreeRADIUS.

There’s some cool stuff I’m working on (not related to OpenVPN); check back here in a few days.

Update: by mistake I reported that StrongSwan also might be vulnerable to the GENERAL_NAMES structure. This is not the case.

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