OpenSSL, a cryptography library for secure communication, fails to validate alternate trust chains in some conditions. In particular this breaks connecting to servers that use Let’s Encrypt certificates, starting 2021-10-01.
For Debian 8 jessie, these problems have been fixed in version 1.0.1t-1+deb8u15.
We recommend that you upgrade your openssl packages.
Further information about Extended LTS security advisories can be found in the dedicated section of our website.