Re: CVE issue flagged in OpenVPN

[Michael Tremer <michael.tremer@ipfire.org>]

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Hello,

> On 9 Nov 2021, at 21:30, Adolf Belka <adolf.belka(a)ipfire.org> wrote:
> 
> Hi All,
> 
> On 08/11/2021 17:48, Adolf Belka wrote:
>> Hi Michael,
>> 
>> On 08/11/2021 17:25, Michael Tremer wrote:
>>> Hello Adolf,
>>> 
>>> Thank you for raising this.
>>> 
>>>> On 8 Nov 2021, at 13:59, Adolf Belka <adolf.belka(a)ipfire.org> wrote:
>>>> 
>>>> Hallo all,
>>>> 
>>>> I had thought, from checks I had made, that there were no security related issues with OpenVPN after the release of 2.5.0 that is currently in IPFire.
>>>> 
>>>> However it has been highlighted in the forum that there is CVE-2020-15078. I have had a look at this and very specific conditions have to be in place for this to be feasible.
>>> 
>>> IPFire systems should not be vulnerable in any configuration because we do not use the affected feature. However, we should of course still upgrade to a fixed version.
>>> 
>>>> So I believe that for the majority of IPFire users this will not be an issue but it could occur if someone is also using one of the OpenVPN plug-ins that are highlighted in the wiki and is also using "--auth-gen-token" or a user-specific token auth solution.
>>>> 
>>>> While the above is unlikely it is not impossible. A fix for this CVE was put into 2.5.2
>>>> 
>>>> I have looked through this release and 2.5.1 to see if there are any changes that might cause a problem for people using earlier features. I don't believe so from first glance but I am not 100% sure. I would want to very thoroughly test it to be sure there would be no unexpected impact.
>>>> 
>>>> Therefore what I am doing is an update that leaves the 2.5.0 source file being used but where I will apply the patches from the commits in 2.5.2 that fix this CVE.
>>> 
>>> We could in theory cherry-pick just the fix for the vulnerability, but on the other hand I do not see anything that has DEPRECATION WARNING in big letters.
>>> 
>>> Also 2.5.4 is out already: https://github.com/OpenVPN/openvpn/releases/tag/v2.5.4
>>> 
>>>> This will give us a quick fix to the CVE in IPFire so even any small chance is closed and then I will look more closely at the later/latest versions and build them and test them to see if I can find any issue, similarly to how Erik and I tested out that 2.5.0 would not break anything. This way we can take time to make sure everything is really working as expected.
>>>> 
>>>> 
>>>> If there is any disagreement to my outlined approach above, please let me know.
>>>> 
>>>> PS:- I have also found why I missed the the existence of the CVE. I was only reading the headlines of the changes from 2.4 to 2.5.4 and the CVE's were only mentioned in the detailed change notes from the involved versions. I know better now how to keep a correct eye on the changes.
>>> 
>>> Usually this should be at least referred to at the top (“Includes security fixes”), or there should be a separate security advisory.
>>> 
>>> I would suggest trying to upgrade to 2.5.4 and see whether that introduces any new regressions. The minor versions should not introduce any change in behaviour.
>> No problem. I will give 2.5.4 a go and see how it goes.
>> Trying just the commit fixes for the CVE has just failed anyway because it couldn't find a member called 'multi_state' so the "simple" fix is not going to be so "simple" anyway.
>>> 
> Have built 2.5.4 successfully and then installed it into my vm testbed system. I have run both my Android Phone ,with OpenVPN for Android app ,and my laptop, with Network Manager applet, and been able to connect through the vpn tunnel with the original 2.5.0 and then also with the 2.5.4 version of OpenVPN.
> 
> The above was with AES-GCM (256 bit) encryption cipher together with SHA2 (512 bit) hash algorithm with the TLS Channel Protection.
> 
> Is that testing sufficient or should I also test out some of the older ciphers in the list like BF-CBC?

I would say that this is sufficient, because if there were any deprecated configuration options used in our configuration file, the daemon wouldn’t start, or the connection would not connect.

I believe this is good enough to go on the list and we should then make a plan about what to do with 2.6.

Thank you for working on this.

-Michael

> 
> Regards,
> 
> Adolf.
> 
>>> However, we are facing a lot of change with 2.6: https://community.openvpn.net/openvpn/wiki/DeprecatedOptions
>> Yes, just had a look at it. All those old weak ciphers will be actually removed. However I would really hope no one is still using ciphers like Blowfish.
>> 
>> Regards,
>> Adolf.
>>> 
>>> Best,
>>> -Michael
>>> 
>>>> 
>>>> Regards,
>>>> 
>>>> Adolf.
>>>> 
>>> 
> -- 
> Sent from my laptop