It was found that several intermediate CA certificates by the eMudhra CA used very weak private keys.
For details, see for example eMudhra Intermediate CA Compromise.
The problem is that the private keys are now public and anyone can issue server certificates with these CAs.
Although the CA certificates with weak keys were revoked, I tested whether eBlocker could be vulnerable to server certificates issued by them.
The short answer is: no, eBlockerOS 3 and 4 are not vulnerable to these CA keys.
More details below...
There could be two potential attack vectors on eBlocker:
- Fake the server certificate for any domain if eBlocker is intercepting HTTPS.
- Fake the certificates of eBlocker's license and update servers: my.eblocker.org, api.eblocker.org and apt.eblocker.org.
Fake any server certificate
eBlocker's certificate validator downloads certificate revokation lists (CRLs) and prevents HTTPS connections to servers with certificates signed by one of the eMudhra CAs with weak keys.
Testing: enable HTTPS and go to https://emudhra.we-have-a-problem.com.
Tests with eBlockerOS 3.2.3 and 4.0.3 were successful: server certificates issued by the revoked eMudhra CAs were not accepted by eBlocker.
Fake license and update server certificates
The license server uses eBlocker's own certificate CAs and roots. If eBlocker tries to connect to a server (my.eblocker.org or api.eblocker.org) with a fake certificate, the Java client on the eBlocker does not allow the connection:
PKIX path building failed: ... unable to find valid certification path to requested target
What about the update server at apt.eblocker.org?
The update server also has a certificate issued by eBlocker's own CA. If the system updater apt-get connects to a fake server it throws the error:
Certificate verification failed: The certificate is NOT trusted. The certificate issuer is unknown. Could not handshake: Error in the certificate verification.
But: even if it would be possible to get the eBlocker to connect to a fake update server, the code signatures would not match with eBlocker's GPG code signing keys, so updates would fail anyway.