Fix OpenSSL Error: Unable To Get Local Issuer Certificate
2 min readFeb 19, 2021
The aim of this little playbook🏁 is fixing
verify error:num=20:unable to get local issuer certificatewhen running certificate chain verifications using OpenSSL with for example
▶ openssl s_client -connect google.com:443
CONNECTED(00000184)
depth=1 C = US, O = Google Trust Services, CN = GTS CA 1O1
verify error:num=20:unable to get local issuer certificateIf you don’t understand certificate chains, watch the explainer first. What’s behind the issue?
- OpenSSL cannot validate the chain OpenSSL itself comes without a list of Trusted Root Certificate Authorities (unlike browsers!)
- I.e., you need to install the CA/s as trusted
- You can do it either one-by-one by downloading a particular cert (with the help of a browser)
- Or (what I do), in bulk by downloading for example
cacert.pempackage from curl - Extract CA Certs from Mozilla - Within OpenSSL itself there are 2 relevant command parameters:
CAfile→ pointing to a single cert trusted as a Root CACApath→ pointing to a folder with certs used as trusted Root CA
- For more, see the How to list certificates, trusted by OpenSSL? — Stack Overflow
1. steps for windows/PowerShell
- download
cacert.pemprovided by curl - Extract CA Certs from Mozilla
Invoke-WebRequest https://curl.se/ca/cacert.pem -OutFile c:\cacert.pem- Run OpenAAL with the
-CAfileflag containing the absolute path to the downloadedcacert.pem
▶ openssl s_client -connect google.com:443 -CAfile c:\cacert.pemCONNECTED(00000184)
depth=2 OU = GlobalSign Root CA - R2, O = GlobalSign, CN = GlobalSign
verify return:1
depth=1 C = US, O = Google Trust Services, CN = GTS CA 1O1
verify return:1
depth=0 C = US, ST = California, L = Mountain View, O = Google LLC, CN = *.google.com
verify return:1
