Looks like that server has another problem, the URL doesn't have any double 
slashes, fails also when not encoded, and a request using POST seems to 
fail as well.

Encoded:

http://ocsp.serpro.gov.br/acserprosslv1/ME4wTDBKMEgwRjAJBgUrDgMCGgUABBTBQ28pKtiXfAbGW%2BhUsNmqSdcYRQQUrRZPS%2FEMvsKKooUY1w1GJZMi480CDQDzmwGvO97JMnso57k%3D

Decoded:

http://ocsp.serpro.gov.br/acserprosslv1/ME4wTDBKMEgwRjAJBgUrDgMCGgUABBTBQ28pKtiXfAbGW+hUsNmqSdcYRQQUrRZPS/EMvsKKooUY1w1GJZMi480CDQDzmwGvO97JMnso57k=

Taking the base 64 request data from the URL above, and decoding the ASN.1, 
we can successfully get the OCSP request:

https://lapo.it/asn1js/#ME4wTDBKMEgwRjAJBgUrDgMCGgUABBTBQ28pKtiXfAbGW-hUsNmqSdcYRQQUrRZPS_EMvsKKooUY1w1GJZMi480CDQDzmwGvO97JMnso57k

On Friday, 8 October 2021 at 23:38:29 UTC+2 [email protected] wrote:

> Could this possibly be the same as the problem I'm encountering with OCSP 
> response for the SERPRO test site (OCSP response not found) when I run this 
> command?
>
> curl --verbose --url 
> http://ocsp.serpro.gov.br/acserprosslv1/ME4wTDBKMEgwRjAJBgUrDgMCGgUABBTBQ28pKtiXfAbGW%2BhUsNmqSdcYRQQUrRZPS%2FEMvsKKooUY1w1GJZMi480CDQDzmwGvO97JMnso57k%3D
>
> (Using instructions from https://unmitigatedrisk.com/?p=42)
>
> See also 
> https://certificate.revocationcheck.com/active-repositorio.serpro.gov.br 
>
> Thanks,
>
> Ben
>
>
> On Thu, Oct 7, 2021 at 6:42 PM 'Jacob Hoffman-Andrews' via 
> [email protected] <[email protected]> wrote:
>
>> Good advice, thanks for sharing! People interested in this may also be 
>> interested in reading Let's Encrypt's 2017 postmortem related to the same 
>> issue: 
>> https://community.letsencrypt.org/t/may-19-2017-ocsp-and-issuance-outage-postmortem/34922.
>>  
>> Another interesting thing: concatenation happens without regard to whether 
>> the OCSP URL in a certificate has a trailing slash. If you issue 
>> certificates where the OCSP URL ends in a trailing slash (rare, I think), 
>> you'll find that all of your OCSP GET requests start with a doubled slash 
>> (//). Also, it's worth being cautious about deploying changes that will 
>> cause large numbers of cache entries to be invalidated.
>>
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>>
>

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